Dengue fever is a mosquito-borne viral infection that resembles flu and can develop into a fatal complication, namely severe dengue fever. The incidence of dengue fever has risen rapidly, mainly in the tropical and subtropical regions. About half of the world’s population is at risk of dengue fever. In some countries, severe dengue fever is a major cause of severe illness and death in children. There is currently no targeted dengue treatment. Early diagnosis and effective care can control mortality rates below 1%.
Ten years after the development of dengue vaccine, various technologies were tried; Sanofi Pasteur successfully developed the quadrifugal live-attenuation vaccine Dengvaxia for more than 20 years, becoming the first dengue vaccine listed in the world. However, it has led to continuous disputes. This article summarizes the development history and current status of dengue vaccine.
I. What is dengue fever
Dengue fever, commonly known as “breakbone fever,” is an acute infectious disease caused by a Dengue virus and is mainly transmitted by the bite of Aedes aegypti or Aedes albopictus. Dengue virus belongs to the Flaviviridae flavivirus genus and there are 4 serotypes (DENV-1, DENV-2, DENV-3, and DENV-4). Four serotypes can infect humans, among which the DENV-2 type is severe. The rate and mortality are higher than other types. The serotype virus does not produce an immune effect and can be repeatedly infected by different serotypes of dengue virus. After Dengue virus infection, the human body can produce persistent immunity against the same serotype virus, but it cannot effectively protect against heterotypic virus infection. If the virus is reinfected with different-type or multiple different serotype viruses, the risk of developing severe dengue fever will be significantly increased. rise.
The clinical manifestations of dengue fever are high fever, headache, muscle, severe joint pain, rash, bleeding tendency, lymphadenopathy, reduction of white blood cell count, and thrombocytopenia. According to the severity of the disease, dengue fever can be divided into two types of dengue fever and severe dengue fever (including dengue haemorrhagic fever and dengue shock syndrome).
There are no specific anti-viral drugs currently available, mainly to take supportive and symptomatic treatment measures. The principle of treatment is early detection, early diagnosis, early treatment, early mosquito isolation. Early identification and timely treatment of severe cases are the key to reducing mortality. Common symptomatic treatment measures include fever, fluid replacement and sedation pain; for severe dengue patients, measures such as anti-shock therapy, blood transfusion, and protection of heart, brain and liver and kidney function should be considered as well as prevention and timely treatment of various complications. Inpatient symptomatic treatment can significantly reduce mortality, from the highest 20% to less than 1%.
Dengue fever threatens about half of the world’s population and is prevalent in tropical and subtropical regions of the world, particularly in more than 100 countries and regions such as Southeast Asia, the Pacific Islands and the Caribbean. WHO has established a reporting system in countries and regions where dengue fever is endemic. In 2015, there were 3.2 million dengue fever cases reported. However, dengue fever is often misdiagnosed due to a wide range of clinical signs with mild non-specific to life-threatening complications, and the limitations of the surveillance system are also responsible for inadequate coverage of dengue cases. The figures released by WHO in 2017 are that there are 390 million dengue fever cases worldwide each year, of which 96 million have clinical manifestations, and another 20,000 people die each year.
II. The WHO is working hard
In the face of dengue fever around the world, the WHO has developed prevention and control strategies on the one hand, and on the other, it has also actively guided various countries in the development and vaccination of dengue vaccines.
Formulate prevention and control strategies
In the face of such a severe trend, WHO launched the 2012-2020 Global Strategy for Dengue Fever Prevention and Control in 2012. The goal is to reduce the death rate by 50% and the incidence rate by 25% from 2020 to 2010.
At the same time, WHO proposes to proceed from the following five aspects:
- Strengthen management and management;
- Comprehensive monitoring and response to the outbreak;
- The continuous control of the vector of infection and transmission;
- The implementation of future vaccination;
- Basic research at the executive and operational level.
Funding to initiate vaccine research
In January 1976, the first meeting of the Southeast Asian Regional Medical Research Advisory Committee (SEA/ACMR) was held in New Delhi, India. At that meeting, the participants reached a consensus to recommend to the WHO Regional Director for South-East Asia the inclusion of severe dengue research as a priority.
In August 1976, the second SEA/ACMR meeting reviewed the spread of the dengue fever outbreak in Southeast Asia and assessed the latest epidemiology, virology, pathogenesis, and clinical management of dengue fever.
In February 1977, the SEA/ACMR Severe Dengue Research Group meeting put forward two priorities: First, vaccine research, and second, control of Aedes aegypti. The first plan for vaccine research was for Southeast Asian and Western Pacific virologists to go to the University of Hawaii College of Tropical Medicine and Clinical Microbiology to receive training in vaccine development. After completing the training, they will return to their respective countries to participate in dengue vaccine development projects.
In 1978, the WHO designated the Department of Pathology, School of Medicine of Ramathibodi Hospital, Mahidol University, Thailand, to undertake the vaccine development task.
In 1980, the WHO began to allocate funds. Mahidol University has set up three laboratories and acquired equipment and operational procedures. It recruited virologists to the University of Hawaii to begin early vaccine research and development.
In 1987, the research team was transferred to the vaccine development center of Mahidol University.
In 1990, experimental animal rooms and vaccine pilot plants were put into operation.
In January 1993, Mahidol University and Sanofi Pasteur signed an agreement to jointly develop a quadrivalent live-attenuated vaccine against dengue fever, which was developed industrially by the latter. Both parties jointly conducted clinical trials.
In 2004, Sanofi Pasteur decided to give up because the DENV-3 strain was reactive and unsolvable.
During the fifteen years from 1980 to 1995, WHO accumulatively funded 2.5 million U.S. dollars, and held special meetings each year from 1983 to 1994 to discuss the progress of vaccine development.
Although it has failed, the WHO has accumulated a great deal of experience in virus strain screening, pharmaceutical development, and clinical trials, laying an important foundation for future vaccine development and the development of relevant guidelines. In addition, Sanofi Pasteur had a deep understanding of the four serotypes of dengue virus in the process, and the process of cooperation with Mahidol University has also accumulated rich experience for subsequent clinical trials in Thailand. Moreover, the virus strain DENV-2 (16681) PDK 53 selected during this period was later used as a skeleton for further research and became an important basis for the Takeda project.
Guide vaccine development
In order to guide the work of various national drug regulatory agencies and individual pharmaceutical companies in the review, review, and approval of vaccines, WHO issued and updated guidelines for the development of first-generation dengue quadrivalent vaccines in 2006 and 2011, covering the first generation. Dengue fever live attenuated vaccine production, quality control, preclinical development and clinical evaluation content, and proposed that the guidelines will be updated with the emergence of the second generation of new vaccine technology. The guidelines state that the evaluation of the safety and efficacy of dengue vaccines should be particularly meticulous, especially the long-term follow-up of vaccine participants after the vaccination, post-marketing studies of vaccines, and the monitoring of the epidemiological and disease burden of dengue fever. system.
In the “2012-2020 Global Strategy for the Prevention and Control of Dengue Fever,” WHO is expected to have a dengue vaccine approved for marketing between 2014 and 2016.
In addition to guiding the industry and national drug regulatory agencies in developing and reviewing and approving relevant vaccine products, WHO also provides guidance for the establishment of relevant vaccination policies and implementation plans for national health and disease prevention agencies.
WHO pointed out that in anticipating the efforts of researchers to develop vaccine products, countries and regions that are endemic for dengue fever should ensure that a strong drug monitoring and monitoring system is established, and immediately begin preparations for vaccination programs, including vaccine product information, and vaccination strategies. The impact of the vaccine on the disease burden and cost-effectiveness, as well as many issues in the implementation of vaccination, such as the inclusion of the national immunization program, vaccine storage and transportation, financial security and so on.
III. The vaccine development
Since there are four serotypes of dengue virus, infection with one of these serotypes does not result in immunization with the other three serotypes, and once re-infected, the severity of the disease will rise significantly, and the industry has reached consensus to develop a quadrivalent dengue vaccine. .
The following introduces several items that enter the clinical stage according to different technologies.
- Traditional live attenuated vaccine
Conventional live attenuated vaccines were obtained by multiple passages in cell culture. People have used this technology to successfully develop smallpox and Sabin vaccines. For the dengue virus, the University of Hawaii developed a method for multiple passages of primary dog kidney cells (PDK). With each virus passage, attenuating point mutations may be generated in the viral genome cultured in a foreign host cell (PDK). In the process of passaging, the main concern is to screen and evaluate the biological properties of the virus with the following attenuation markers:
- Replicate under certain temperature conditions
- Smaller plaques
- Cytopathic effect
- Mouse neurotoxicity
- Human monocyte growth
In general, 10-50 passages are required to obtain a vaccine candidate.
The advantage of this method is the continuous humoral immune response and cellular immune response, which have extensive antigenic responses to viral structural proteins and non-structural proteins. However, there is also a theoretical risk that it is possible to convert to a toxic wild phenotype, especially in tetravalent virus compositions. In addition, there is a virus or immune interference between different serotypes in this tetravalent vaccine.
Thai Mahidol University II failed
All four serotype strains from Mahidol University were isolated from severe Dengue-infected patients in Southeast Asia and were passaged on mammalian cells and then inoculated intrathoabally to the Toxorhynchites amboinensis or Aedes aegypti. Non-arbitrary viruses, because only arboviruses can migrate into the salivary glands of mosquitoes after intrathoracic administration. The head of the mosquito was then removed and ground to obtain a pure virus strain.
Next, serotype 1, 2, and 4 viruses were passaged in primary dog kidney cells (PDK) every 5-10 days at 32°C, while serotype 3 viruses were passaged through green monkey kidney cells (GMK). Finally attenuated culture in fetal rhesus monkey lung cells (FRhL) to obtain virus strains suitable for vaccines, namely:
- DENV-1 (16007) PDK13 (No. 16007 serotype 1 passaged in primary dog kidney cells for 13 generations)
- DENV-2 (16681) PDK53 (Number 16681 Serotype 2 Passaged in Primary Dog Kidney Cells for 53 Generations)
- DENV-3 (16562) GMK30 FRhL 3 (Number 16562 serotype 3 is passaged in green monkey kidney cells for 30 passages after passage in green monkey kidney cells)
- DENV-4 (1036) PDK48 (passage number 1036 serotype 4 passaged in primary dog kidney cells for 48 passages)
In phase 1 clinical trials of monovalent, bivalent, and trivalent vaccines, DENV-1 (16007) PDK 13, DENV-2 (16681) PDK 53, and DENV-4 (1036) PDK 48 performed basically acceptable, among which The best performance was achieved with the DENV-2 (16681) PDK 53. However, DENV-3 (16562) GMK 30 FRhL 3 had a certain degree of reactogenicity compared to the other three virus strains in the first-valent test. In addition, in the phase II trial of the tetravalent vaccine, interference was observed after adding DENV-3 (16562) GMK 30 FRhL 3 . Later, DENV-3 was further screened to obtain DEN-3 GMK33 FRhL 2. Sanofi Pasteur also found further investigations on the DENV-3 strain by the US Centers for Disease Control and found that the virus strain was also divided into two types, one being a attenuated type and the other being a toxic wild type. In follow-up clinical trials, the DENV-3 strain was also observed to be reactive and not suitable for vaccines. For this reason, Sanofi Pasteur chose to give up.
GlaxoSmithKline TDENV LAV Shelved
The Walter Reed Army Institute of Research (WRAIR), a research institute of the US Department of Defense, also used the same technology to obtain the candidate strains DENV-1 45AZ5 PDK-20, DENV-2 16803 PDK-50, DENV-3CH53489 PDK-20, and DENV-4 341750 PDK-20. Later, GSK also joined the project research.
In a number of clinical trials, the immunogenicity and reactogenicity of different virus strains were difficult to balance, such as fever and viremia, although the number of passages was readjusted, but the titer was between the theoretical value and in vitro and in vivo. There are big differences, and the vaccine production process is very complicated, so the two sides have differences. GlaxoSmithKline abandoned the project, and WRAIR plans to use it as a reinforcing agent.
2. Recombinant subunit vaccine
Developed by Merck, V180 is an inactivated vaccine that contains only truncated versions of structural envelope proteins. Specifically, the amino-terminal 80% envelope protein (extracellular region) is preserved, and the C-terminal 20% envelope protein (transmembrane region) is removed, so that it can be extracellularly secreted and can be easily purified while retaining the antigen and also avoiding differences. The serotypes interfere with each other. Since the inactivated virus itself is difficult to elicit immunity, the inactivated vaccine must be used in conjunction with an adjuvant to stimulate immunity. V180 must be given three doses, each at a time interval.
Clinical trials were formally launched in 2012 and completed Phase I studies by 2014. In collaboration with the National Institutes of Allergy and Infections, National Institutes of Health, 2015, for subjects who have been vaccinated with live attenuated vaccines such as TV003 or TV005. No follow-up reports.
3. Inactivated purified vaccine
Inactivated vaccines can effectively avoid the risk of virus interference and conversion to pathogenic phenotypes, but there are also disadvantages of structural changes of the viral proteins during inactivation and the inability of the inactivated virus to expand.
GlaxoSmithKline’s TDENV PIV is an inactivated vaccine that has been purified and contains only inactivated dengue virus. In preclinical experiments, TDENV PIV was inoculated with adjuvant in two doses at intervals of 4 weeks. Clinical trials were formally launched in 2012 and were conducted in the United States and Puerto Rico respectively, a low endemic area and a high endemic area. Another 1/2 phase trial with different adjuvants AS03B using different inoculation cycles. The results are expected to be announced in 2018.
This project is a joint collaboration between the Walter Reed Army Institute of Research (WRAIR) and GlaxoSmithKline, and the participation of Fiocruz and Bio-Manguinhos, research institutes of the Brazilian Ministry of Health.
4. Chimeric attenuated live vaccine
By means of genetic engineering technology, flavivirus was used as the backbone to replace the anterior membrane protein and envelope protein with the corresponding gene segments of the ideal virus strain. In this way, the attenuated phenotype is obtained and the target antigen can be expressed. The advantage compared to traditional live attenuated vaccines lies in the accuracy of construction. Chimeric vaccines have a standardized attenuated backbone sequence that eliminates the possibility of genetic recombination between viral strains present in conventional vaccines. In addition, the risk of virus or immune interference between different serotypes can also be reduced.
National Institutes of Health (NIH) National Institute of Allergy and Infection (NIAID) TV003 in phase 3 clinical trial
This is a live attenuated vaccine that combines recombinant serotype 4 non-structural genes with serotype 2 structural genes. The vaccine can induce antibodies and cellular immune responses, and only one dose can produce sufficient immunity.
NIAID has transferred TV003 to various agencies, including Instituto Butantan in Brazil, VaBiotech in Vietnam, Panacea Biotec in India, Serum Institute of India and Indian Immunologicals in Serum, Medigen Biotech in Taiwan, and Merck East (V181). Clinical trials were formally launched in 2011. Brazil’s Instituto Butantan is currently conducting a large-scale phase III trial in Brazil. Phase II trials are underway in Thailand and Bangladesh.
Takeda DENVax (TDV, TAK-003) is in phase 3 clinical trial
This is a live attenuated vaccine that uses recombinant technology to bind serotype 2 non-structural genes to serotype 1, 3, and 4 structural genes. Among them, the virus strain DENV-2 used as a skeleton was originally derived from DENV-2 (16681) PDK 53 developed by Mahidol. The vaccine must be given two doses at intervals of 3 months.
Clinical trials were formally launched in 2010. In May 2013, Takeda bought Inviragen for US$215 million to acquire DENVax, which was already in Phase 2 at the time. The phase 2 results announced in November 2017 showed that the immunization effects of children aged 2-17 years after vaccination lasted for 18 months, regardless of previous infection with dengue fever. Phase 3 trials are currently underway and are expected to be completed by the end of 2018.
Sanofi Pasteur CYD-TDV First Approved Globally in December 2015
Like DENVax and TV003, CYD-TDV is also a live-attenuated vaccine, but the latter uses recombinant technology to bind the non-structural genes of yellow fever virus to all four serotype dengue virus structural genes. The vaccine was inoculated with three doses of 6 months apart at a time span of 1 year.
Clinical trials were formally launched in 2009. Two parallel three-stage randomized trials completed the efficacy monitoring period at the end of 2014 and submitted listing applications in various countries in early 2015. Finally, they were approved in Mexico, the Philippines, and Brazil in December 2015. The vaccine is called Dengvaxia.
IV. The Birth of Dengvaxia
Sanofi Pasteur’s development of dengue vaccine dates back to 1993 when it co-developed the first live quadrivalent live-attenuated vaccine for dengue fever in collaboration with Mahidol University in Thailand, but later collapsed in Phase II clinical trials. This project will be around 2004. termination. Despite the failures, Sanofi Pasteur had a deep understanding of the four serotypes of dengue virus in the process, and the process of cooperation with Mahidol University has also accumulated rich experience for subsequent clinical trials in Thailand.
Sanofi Pasteur did not give up on the road to pursue the dengue vaccine and was always looking for new opportunities. Finally in July 2008, Sanofi Pasteur acquired Acambis, a vaccine development company with headquarters in London, United Kingdom and R&D labs and production facilities in the United States, for US$546 million. The company’s R&D projects include West Nile virus, influenza virus, Japanese encephalitis, Clostridium difficile, and smallpox vaccines. In the field of dengue vaccines, Acambis uses recombinant technology to insert the flavivirus anterior membrane protein and envelope protein into the yellow fever virus (YFV) 17D backbone, resulting in a dengue virus chimera. In fact, the technology originated from the National Institutes of Health (NIH) and Saint Louis University, and Acambis optimized it.
The Dengue Fever vaccine developed by Sanofi Pasteur is a recombinant yellow fever 17D dengue virus attenuated live quadruple dengue vaccine (TDV), commonly known as CYD-TDV (chimeric yellow fever dengue-quadruple dengue vaccine ).
There are four serotypes of dengue virus. Therefore, when developing a vaccine, it is necessary to first select four wild type dengue viruses. They are Thailand strain PUO-359/TVP-1140 (serotype 1) and Thailand virus strain PUO-218 ( Serotype 2), Thailand strain PaH881/88 (serotype 3) and Indonesian virus strain 1228 (TVP-980) (serotype 4). Recombinant technology was used to replace the structural genes of the four wild-type dengue viruses with the genes encoding the yellow fever virus 17D (YFV 17D) premembrane protein (prM) and envelope protein (E), respectively. Recombinant Dengue vaccine virus. The four recombinant viruses were mixed together to obtain a single vaccine, namely CYD TDV. As a result, the CYD-TDV vaccine candidate contained four recombinant live attenuated virus strains based on the yellow fever virus 17D (YFV 17D) (CYD-1, CYD). -2, CYD-3, and CYD-4), each of which express a gene for one of the four dengue virus serotypes.
The CYD TDV vaccine contains 4.5-6.0 log 10 CCID50 of each of the four dengue virus strains (the median cell culture infectivity) for each dose, and is supplemented with excipients to make lyophilized dosage forms without adjuvants or preservatives.
- Genetic stability. The entire genome sequences of the four recombinant virus strains (CYD-1, CYD-2, CYD-3, and CYD-4) remained stable during the entire process of vaccine production, from the first pass to the study of seed batches, master seed batches, and later The process (passage 10 times or more) has good stability.
- Phenotype stability. As with genetic stability, the plaque size phenotype of the four recombinant virus strains (CYD-1, CYD-2, CYD-3, and CYD-4) remained stable throughout the production process. The neurotoxicity in the suckling mouse model is low and stable, and can replace nonhuman primate models. At present, the suckling mouse model is used for control in daily production.
- Post-translational modifications such as glycosylation. Both sites of the four recombinant strains (N67 and N153) have high mannose and complex/mixed glycosylation, which is consistent with the ability to interact with DC-SIGN.
- Preclinical immunogenicity evaluation. In vitro immunogenicity: Four recombinant virus strains (CYD-1, CYD-2, CYD-3, and CYD-4) were shown to be associated with the parent virus (wild type dengue virus) in single cell-derived dendritic cells (mDCs). Similar growth kinetics to YFV 17D). Four recombinant virus strains (CYD-1, CYD-2, CYD-3, and CYD-4) induced maturation and controlled response of dendritic cells, with limited production of inflammatory cytokines and the same expression of antiviral type 1 interferon. In the human hepatocyte cell lines THLE-3 and HepG2, the expression levels of the four recombinant virus strains were significantly lower than that of the YFV 17D virus.
- In vivo immunogenicity: The recombinant virus strain tetravalent vaccine (CYD-1, CYD-2, CYD-3, and CYD-4) is immunogenic in monkeys, induces a degree of viremia, resistance to serotype 1-4 wild Dengue virus attack. The monovalent CYD-2 strain also induces certain protective effects, as well as faster clearance. Adjusting the serotype dosage and dosing period can reduce the interference between serotypes.
- Non-clinical safety. Non-clinical safety assessments included topical tolerable repeat dosing, biodistribution, neurotoxicity, and developmental and reproductive toxicity assessments. The CYD dengue virus has low levels of distribution and transients at the injection site, lymphoid tissue, and liver. No nerve affinity. In studies of developmental and reproductive toxicity, rabbits and mice were given human doses of the CYD dengue vaccine. No side effects were observed on mating and fertility, and no teratogenic effects were observed. No effects on the production were observed.
- Theoretical risk. The use of arthropods as the medium of transmission: the lack of laboratory or Aedes aegypti or Aedes albopictus as the media. Lack of lice as the medium of communication. With low levels of host viremia, there is little or no risk of the vaccine virus spreading to the environment.
- Reversion Mutation Toxicity: Wild type yellow fever virus is not likely to be produced in vaccine recipients. 1) Deletion of YFV 17D envelope gene; 2) Multiple back mutations to wild type attenuated mutations in 7 non-structural genes and core protein genes Residues.
- Reorganization: Natural recombination is almost impossible, and forced recombination in in vitro systems will not occur. In addition, the data obtained in the artificial recombination fully indicates that even if recombination occurs, no disease or spread in the environment will occur.
- Organ Affinity: The hepatotropic and kidney-feeling of CYD dengue vaccine was lower than YFV 17D. Clinical trials and postmarketing surveillance will be studied in depth.
- Activation/antibody-dependent enhancement: Early development stages and follow-up clinical trials and long-term follow-ups are concerned with possible risks. In vitro studies did not find differences between serotypes, but phase III trials showed different effects. If there is a drop in immunity for a serotype, you can consider a strong dose.
- Early clinical evaluation. Immunogenicity and reactogenicity, including neutralizing antibodies and T cell responses: Phase I and II clinical trials involving young children and adults, four recombinant virus strains can induce a neutralizing response (PRNT) and are non-reactive. The dengue virus pre-immune force will have a higher and more extensive neutralizing response. Cell-mediated immunity: CYD-TV dengue vaccine induced anti-dengue serotype specific Th1/Tc1 and anti-YF17D NS3 specific CD8 responses. Dengue pre-immunity or booster vaccination expands cell-mediated immune responses. After dengue-positive individuals were inoculated, anti-dengue NS3-specific CD8 responses disappeared.
- safety. Phase I and II clinical trials have no safety issues.
Phase IIb proof-of-concept clinical trial
From February 2009 to February 2010, a total of 4002 4-11-year-old children were recruited in Thailand for the Phase IIb proof-of-concept efficacy and safety single-center trial clinical trials with a 2:1 ratio of subjects (2669 persons: 1333 persons). ) Three dengue vaccines or control drugs (rabies vaccine or placebo) were randomized in October, June and December. Subjects were then followed up until 25 months. The primary goal of the trial was to evaluate the effectiveness of preventing virological confirmation of symptomatic dengue fever during at least 1 month up to 25 months after the third vaccination, regardless of severity or serotype (as analyzed by protocol).
Among the 3,673 people who were included in the preliminary analysis (2,452 in the vaccine group: 1,221 in the control group), 134 confirmed virological dengue fever and serotype 2 predominated. In the intent-to-treat population (subject to at least one dose), the overall efficacy was 30.25% (95% CI; -13.4-56.6), and the efficacy of each serotype was 61.2% of DEN-1 (95% CI) :17.4–82.1), 81.9% of DENV-3 (95% CI: 38.8-95.8), 90.0% of DENV-4 (95% CI: 10.6-99.8), and only 3.5% of DENV-2 (95% CI: – 59.8 – 40.5) This may be due to the fact that serotype 2 is the predominant type during the trial. However, the plaque reduction neutralization assay (PRNT50) after 28 days of the third vaccination showed that the immunogenicity level was good and that each serotype was comparable.
Dengue fever vaccines are well tolerated for up to two years of efficacy monitoring and no safety signs appear. Then a four-year safety monitoring period was carried out, which lasted for six years from the first dose. The entire experiment was completed in 2016.
Two Phase III clinical trials
These two phase III clinical trials recruited a total of 10275 subjects aged 2-14 in the five Asian countries (Indonesia, Malaysia, the Philippines, Thailand, and Vietnam) and five Latin American countries (Brazil, Colombia, Honduras, Mexico, and Puerto Rico) A total of 20,869 9-16 year old subjects. Subjects were randomly assigned to receive a vaccine or placebo (0.9% physiological saline) 2:1. The study protocol included a period of 13 months after the last vaccination or a 25-month monitoring after the first vaccination as the primary efficacy endpoint, followed by a 4-year follow-up of safety monitoring.
The results of these two phase III trials were published in the New England Journal of Medicine in 2014. A total of 31,000 children aged 2-16 years were involved. The results showed that the overall efficacy for symptomatic dengue fever was 56.5% in Asia and 60.8% in Latin America, and the safety was good during the 25-month monitoring period. For serotypes, Type 1 (50.2%, 95% CI 35.6%–61.5%) and Type 2 (39.6%, 95% CI 18.7%–55.2%) were less effective than Type 3 (74.9%, 95% CI 65.1) %–82.0%) and type 4 (76.6%, 95% CI 65.0%–84.4%).
Importantly, both trials showed that severe dengue fever and dengue hospitalization were significantly reduced during the 25-month monitoring period; in Asia, severe reductions were 80% and hospitalizations were reduced by 67.2%; while in Latin America, severe dengue fever was reduced by 95%. Hospitalization decreased by 80.3%.
The incidence of systemic adverse events in CYD TDV vaccinators was 66.5%, compared with 59% in the placebo group. The most common systemic adverse events were headache (>50%), discomfort (>40%), myalgia (>40%).
The need to be vigilant is that in the third year after the first dose in the 2-5 age group, 15 cases of CYD TDV vaccinations occurred, compared with 1 placebo group; all other age groups were at comparable levels. This may be due to the high serum-negative rate in this age group. Vaccination is equivalent to a silent natural infection. Once it is really infected with dengue fever, it is equivalent to a second infection, and the risk of serious illness is greatly increased. Therefore, in the setting of inoculation for the crowd, this age group was removed and, with caution, the 6-8 age group was also removed.
V. Usher in dawn
On December 9, 2015, Sanofi Pasteur announced that Dengvaxia, a dengue vaccine developed by the company, has been approved by the Federal Mexican Federation for the Prevention of Health Risk (COFEPRIS) for the prevention of all persons aged 9 to 45 years living in dengue fever endemic areas. Diseases caused by the four serotypes of dengue virus became the first approved dengue vaccine product in the world.
The approval of Dengvaxia is based on an extensive clinical development project involving more than 40,000 volunteers who live in 15 countries and have different ages, geographic regions, epidemiology, ethnicities, socioeconomic backgrounds. . Among them, Mexican dengue epidemic areas participated in all phase I, II, and III clinical studies of the Dengvaxia clinical development project. Dengvaxia’s approval marks that dengue has been transformed into a vaccine-preventable disease, which is a historic milestone for the global public health community, especially for about half of the world’s population living in dengue risk. .
Immediately afterwards, in December, the Philippines and Brazil also approved Dengvaxia, a Dengue vaccine. So far, it has been approved and listed in 11 countries including Mexico, Philippines, Brazil, El Salvador, Costa Rica, Paraguay, Guatemala, Peru, Indonesia, Thailand, Singapore, and Venezuela, Honduras, Malaysia, Australia, Argentina, Bangladesh and Cambodia. Eight other countries have been approved but have not yet been listed. Therefore, Dengvaxia has covered many high-risk dengue fever countries.
On July 29, 2016, the WHO made a special statement on the report of Sanofi pasteurization of sanofi paste, and recommended that countries should introduce this dengue vaccine in areas with high burden of disease based on epidemiological data, and from public health impacts and economic effects. From the point of view, when determining the inoculation target population.
In its report, WHO recommends:
- The seropositivity rate of patients with dengue virus infection in any previous serotype among different age groups should exceed 70%.
- The positive rate of seroprevalence is between 50% and 70%, but the public health influence will be reduced.
- For age groups with seropositivity below 50%*, vaccination is not recommended.
- The use of a seroprevalence rate greater than 50% is based on a phase III clinical trial design and the different manifestations of the vaccine between seronegative and positive populations. In phase III clinical trials, the overall seropositivity rate for people aged 9-16 years is 80%. It is not recommended to use this vaccine in people with low seroprevalence because the vaccine is not effective in this population and there is a risk of severe dengue fever in the long term.
- WHO also mentioned that the risk of dengue fever and dengue fever after vaccination in the 2-5 age group is high and therefore cannot be used in this age group. It is also prudent and not suitable for 6-8 years old. Therefore, this product is suitable for people aged 9 years old and above.
- The WHO also pointed out that the vaccination may not be effective or theoretically even increase the risk of hospitalization or severe dengue in people who have been seronegative at the time of first vaccination, regardless of age. In a seronegative population, the vaccine is equivalent to a silent natural infection, making the seronegative vaccinated population equal to experiencing a second infection at the time of first exposure to the dengue virus, and the second dengue infection developing a severely increased risk of infection. . The younger the age, the higher the probability of seronegative.
- The WHO also pointed out that because this vaccine needs to be vaccinated three times and each time interval is 6 months, the time span spans 1 year, which requires establishing a good vaccine tracking and monitoring system.
Based on the large population base of the countries and regions where dengue fever is rampant, the epidemic has caused great harm, the world’s first product has been approved for listing and is highly efficient, and WHO has recommended it. Sanofi Pasteur ranks Dengvaxia as an important pillar of its future performance growth. It is not surprising. To this end, Sanofi Pasteur also invested 300 million euros in the establishment of a new factory in Neuville sur Saone, France, specializing in the production of dengue vaccine, with an annual production capacity of 100 million doses.
Sanofi Pasteur further stepped up the pace of listing applications in relevant countries, and on the other hand, promoted the national vaccination program in product approval countries. This is also in response to the WHO’s call to achieve the 2020 goal. After all, the approval of the vaccine is only to resist the dengue fever epidemic. The first step, more importantly, is to conduct a comprehensive promotion of vaccination.
In April 2016, the Philippines launched the Dengue Vaccine Public Inoculation Project, which plans to inoculate dengue vaccine for 1 million students aged 9 and above from 6000 public schools. This is the first public dengue fever vaccination project in the world. The project will purchase DH$3.5 billion (US$70 million) worth of Dengue vaccine products from Sanofi Pasteur. Before this, the dengue vaccine was started in February at his own expense. As of November 2017, more than 730,000 Filipino children have been injected with the vaccine, plus more than 830,000 people have been inoculated at their own expense. The Philippines reported more than 200,000 cases of dengue fever in 2013.
In August 2016, the public vaccination program was launched in Parana, Brazil. As of November 2017, 300,000 people had received dengue vaccine. The state reported 55,000 dengue cases in 2015 and 1.4 million cases throughout Brazil. Total medical expenditure in Brazil due to dengue fever is US$1.2 billion.
In September 2016, Mexico began inoculating dengue vaccine at its own expense. The public vaccination program is also in progress and has been approved by the National Vaccination Committee.
As of November 2017, Sanofi Pasteur has listed dengue vaccines in 11 countries that have been approved, with the Philippines and Brazil launching public vaccination projects.
Here is a section of our country. All provinces in China have imported case reports, mainly in southern provinces such as Guangdong, Yunnan, Fujian, Zhejiang, and Hainan. In 2017, there were 5893 cases of dengue fever in China, which was about one-tenth of the number of AIDS cases, including 2 deaths. Sanofi Pasteur also stated in September 2017 that it plans to submit a listing application in China. In addition, some preparatory work is being done to conduct epidemiological studies in southern China in order to further confirm the burden of dengue fever.
VI. A head-on blow
The Brazilian and Philippine governments have launched universal vaccinations. Mexico is also promoting universal vaccinations. Many countries have been approved and listed. As Sanofi Pasteur is taking advantage of Dengvaxia’s bright future, more research data is gradually emerging. It’s like a stick.
On November 29, 2017, Sanofi Pasteur announced new follow-up data for the Dengvaxia clinical trial, which shows that the patient’s response to Dengvaxia differed from whether they had contracted dengue fever in the past. In other words, the vaccine works as expected for people who have been exposed to the virus, but the use of vaccines for those who have not been infected with the dengue virus may lead to an increased risk of serious illness from subsequent dengue infection.
Specifically, for those who have been infected with dengue fever, the number of hospitalized cases due to dengue fever is reduced by 15/1000, and severe dengue fever is reduced by 5/1000; however, after vaccination has been conducted for people who have not been infected with dengue fever, As the number of hospitalized cases of dengue fever rose by five-tenths, cases of severe dengue fever rose by two-tenths. At the same time, Sanofi Pasteur emphasized that critically ill patients have already recovered.
When the news came out, it was a loss. In particular, the implementation of the public vaccination program in public schools in the Philippines is for children aged 9 and above, of whom approximately 70,000 are never infected with dengue fever. More than a dozen children in the Philippines have reported severe dengue fever and even unfortunate deaths after receiving dengue vaccine.
The Philippines immediately suspended Dengvaxia sales, terminated the public vaccination program, and started investigating the possible harm caused to the vaccinated population. The vaccination program made wrong decisions and possible corruption. Of course, the sanofi pasteur was blamed. The biggest doubt was to hide the truth. And eager to be successful. Even the WHO can not get away with: In order to achieve the 2020 goal, there is an urgent need for vaccine products and Sanofi Pasteur is strongly endorsed, ignoring possible risks.
The Philippines demanded that Sanofi Pasteur return all vaccine purchase costs of 3.5 billion pesos (about 70 million US dollars), including 800,000 doses of vaccines that have not yet been used, worth about 800 million pesos. In addition, the Philippines also requires Sanofi Pasteur to perform serum tests for vaccinated people free of charge to further assess possible risks. In January 2018, Sanofi Pasteur agreed to compensate 1.4 billion pesos (about 28 million US dollars), and is willing to bear the costs incurred due to adverse reactions caused by Dengvaxia. In addition, Sanofi Pasteur will cooperate with the Philippine government to conduct more investigations.
Brazil also strictly investigates and limits the vaccinated population. Fortunately, Brazil only implements universal vaccinations in the Parana state, with little impact. Other listed countries only inoculated at their own expense and did not spread out in large areas.
Globally, Sanofi Pasteur will update the vaccine instructions and conduct more research to clarify the safety of the vaccine and the applicable population. However, in any case, the medical staff must evaluate the individual’s possibility of contracting dengue fever before inoculating Dengvaxia with the vaccine. The vaccine can only be used for people who have been infected with dengue fever.
In fact, as early as when WHO recommended Dengvaxia, it was also clearly stated that vaccination should be conducted among sero-positive people. Simply dividing the population according to age is still inadequate. In theory, the general promotion of vaccination among people in recommended age groups will be of great benefit to public health. However, it is controversial that for those who are seronegative, there is a small hidden danger. Is this public health measure fair?
If there is reliable seroprevalence data, this problem will be solved. However, because the investigation of serum epidemics is not only very time-consuming, it also requires a large amount of investment, but also requires professional and technical personnel, and this result is dynamic, so it is difficult to obtain a reliable data.
Another approach is to use sero-positive people to select and arrange for vaccination prior to vaccination, excluding seronegative individuals. Neutralization assay for plaque reduction (PRNT) is currently the most commonly accepted method for detection of dengue antibodies. However, this method is very tedious and does not spread widely. Moreover, the virus titer varies greatly under different detection conditions. Serological detection is simple and practical, but it needs further verification. Dengue fever immunoglobulin testing is a good method, but at present, only in a few countries, private institutions have such detection methods, and are not widely used. It seems that a simple, accurate, cheap, and easy to operate bedside inspection (POCT) is very urgent.
In turn, the performance of Dengvaxia’s vaccine product was not as promising as expected. Analytical institutions once forecasted sales of 200 million euros in 2016 and 360 million euros in 2022. However, the reality is far from satisfactory. The actual income in 2016 was 55 million euros. In the first 9 months of 2017, there were only 22 million euros. Sanofi Pasteur attributed the reason that the vaccine-applicable population is 9-45 years old is more difficult to implement than the younger age or older age groups. The inoculation project, together with the lighter outbreak of dengue fever in Brazil and Mexico in 2017, made people lack a sense of urgency.
Obviously, for Sanofi, who spent more than 20 years and US$1.5 billion to develop Dengvaxia, this is a loss. However, Sanofi now considers that it is not possible to recover the economic losses, and more still avoid more severe public health crisis, product improvement and repositioning, as well as the development of better dengue vaccine products. In early December of 2017, Sanofi announced on its own initiative that due to its responsibility to consumers, the relevant national regulatory agencies have been advised to update the prescription information of vaccines and no longer recommend the use of dengue vaccines.
Regardless of Dengvaxia’s path, Sanofi was considered a great attempt. What needs to be recognized is that the dengue virus is still raging everywhere, and it is possible to have an outbreak at any time and deprive people of their health and lives. Humankind is still in desperate need of a safe and effective vaccine and urgently needs more pharmaceutical companies to participate in it. Takeda’s Phase III clinical trial is expected to be completed by the end of 2018 and the results are still unknown. Given the controversial issues with Sanofi Pasteur’s products, Takeda needs to be more rigorous and perfect, and pharmaceutical supervisors in various countries must be more cautious.
For a long time, infectious diseases have been the enemy of human health. In the course of the struggle with it, humans invented the vaccine and eliminated or basically eliminated many infectious diseases. However, there are many infectious diseases that we need to face, such as dengue fever. Although the road to vaccine development has always been full of hardships, scientists have never stopped.