With the slogan “Immunization for a healthy future. Know, Check, Protect” WHO reminds us this week that vaccines prevent 2-3 million deaths each year. Just imagine this: 2 to 3 million lives. This equals the populations of countries like Mongolia or Botswana.
As we celebrate the contribution of vaccines to public health, World Immunization Week also gives us the opportunity to appreciate and reflect on ongoing innovations in the field. The development of a dengue vaccine, which has accelerated dramatically in these last years, shows that there is much more to come in the future of immunization.
First, what is dengue?
Dengue is a virus that causes fever, headache, skin rash, and debilitating muscle and joint extreme pains, so much so, that it’s been known as the “breakbone fever.” In some cases it can lead to circulatory failure, shock, coma and even death. There are four different strains of the virus, called serotypes, that cause disease in humans.
Dengue does not spread from person to person. People contract dengue through the bite of the Aedes aegypti mosquito, which lives mainly in urban areas of tropical and semi-tropical regions like Africa, Asia, Latin America and the Caribbean. The mosquitoes usually breed in water containers, flower pots, old automobile tires, buckets and other discarded items that collect rainwater.
So far, strategies to prevent dengue have focused on eliminating mosquito breeding sites by way of emptying these water containers and using insecticides. But, rapid population growth, urbanization and increased international travel make it harder and harder to control the mosquito and its spread.
According to the WHO, the disease has increased 30-fold in the last 50 years, infecting more than 100 million people and putting at risk almost half of the entire world’s population. Making matters even more alarming, a recent study found that dengue infections are extremely underestimated: there could be as many as 400 million per year.
Where are we on a dengue vaccine?
Dengue vaccines have been under development since the 1940s with little progress until the 1990s -- partly because there was limited understanding and awareness of the disease. On top of that, developing a dengue vaccine is particularly challenging because in order for it to be completely effective it must immunize against all four serotypes that transmit the disease.
Today, different vaccine candidates have passed exploratory and pre-clinical stages and are now undergoing clinical trials.
Currently, the French pharmaceutical company, Sanofi Pasteur, has a vaccine candidate that is being evaluated in Phase 3 studies. In fact, this Monday, April 28, Sanofi Pasteur announced that it had completed its Phase 3 trial in Asia—the first Phase 3 large-scale efficacy study of a dengue vaccine ever completed. The full results are not yet publicly available, but WHO welcomed the encouraging news, stating it would provide an independent assessment of the data once the complete analysis is publicly available and that it continues to await the results of another Phase 3 study in Latin America.
Two other vaccine candidates, one developed by Takeda, and another by the U.S. National Institutes of Health and the Butantan Institute in Brazil are undergoing Phase 2 trials. Merck with ISCOM in Australia and GlaxoSmithKline with the Oswaldo Cruz Foundation in Brazil, are conducting Phase 1 trials.
Setting the stage
While dengue vaccines are being tested, public health experts, multilateral and non-profit organizations, academia, and international and local communities are working together to support countries as they consider vaccine introduction. You might wonder: why invest time and effort in preparing for a vaccine that is not here yet? In the past, some vaccines have taken decades to reach the most vulnerable populations. With dengue outbreaks on the rise, the ideal scenario would be to introduce a safe and effective vaccine as swiftly as possible to prevent the disease.
Partnerships like the Dengue Vaccine Initiative (DVI), of which Sabin is a member together with WHO, IVI (International Vaccine Institute) and IVAC (International Vaccine Access Center at the Johns Hopkins University Bloomberg School of Public Health), seek to lay the groundwork to inform decision-making related to introducing a dengue vaccine.
In celebrating this year’s World Immunization Week, we invite you to stay updated on dengue, join the conversation, and help us find a solution to fight this disease.
Photo by Lukas Hofstetter