Dengue is a viral disease caused when bitten by a specific type of mosquito known as an Aedes aegypti. This virus has four varieties, known as serotypes – DEN-1, DEN-2, DEN-3, and DEN-4. 

When you get infected, data shows that you are likely to have very long-term protection against the serotype that infected you. However, data also shows that you do not have strong, if any, protection against the other three serotypes. 

This makes it challenging to create vaccines, particularly because research shows that symptoms tend to get worse with each infection. In some cases, a dengue reinfection can become serious, leading to something like hemorrhagic fever – a type of fever that can cause serious bleeding, a sudden drop in blood pressure (shock) and death – or dengue shock syndrome – essentially a sudden decrease in the flow of blood. 

Until recently, there have been no specific treatments or vaccines for dengue fever. Dengavaxia (also known as CYD-TDV) is the world’s first dengue vaccine to be approved anywhere in the world. The vaccine was licensed in 2015 in Mexico and has since been approved for use in several countries in Europe, Asia, and the Americas. The vaccine is given through a set of three doses each six months apart. 

Dengavaxia’s clinical trials were held in 11 countries in Asia and Latin America. Data from Phase-3 trials – the last stage of vaccine research – show that the vaccine was 82% effective at protecting against dengue virus among participants ages 9-16 who had been infected with the virus before. 

Researchers continued to track outcomes in the first 25 months following the vaccine and found that the vaccine was 76% effective at protecting against dengue virus among the same participants, showing that efficacy lasted well over that period of time. The trial data also found that the vaccine was 79% effective at protecting against hospitalization from infection with a dengue virus over 5 years. Dengavaxia was also found to be effective against all four dengue virus serotypes, though most effective against DEN-4 (89% effective) and least effective against DEN-1 and DEN-2 (67% effective).

However, data has found that the vaccine works better for some more than others, which impacted who the vaccine was approved for. For instance, the vaccination was not very effective in age groups <9 years old, which is why the age of 9 has been set by health bodies like the WHO as the minimum age to get the vaccine. 

In addition, a follow-up study found that health outcomes of being infected with dengue were actually worse among those who got vaccinated who had not already been infected with dengue compared to those who were unvaccinated who had not already been infected with dengue. This finding is why health bodies have only approved the vaccine for those who have already been infected with dengue.

There are short-term adverse reactions among people who are vaccinated, regardless of whether or not they have been previously infected. Common reactions include headache, pain at the injection site, tiredness, and muscle pain.

The strong findings in the trial and lack of safety concerns has led the WHO to recommend Dengavaxia to people 9 to 45 years of age who have been infected with the dengue virus one time. The regulatory body of the United States, FDA, has approved the use of Dengvaxia for people 9 to 16 years old in regions with high rates of the disease after a lab test that confirms they have had one previous infection with dengue.

Dengue is widespread in the Philippines, and the updated studies that the Dengvaxia vaccine can have adverse effects on those that were not previously infected caused widespread fear for the safety of their children. Furthermore, there are no rapid tests available to people to determine if someone has been previously infected before they are administered the vaccine.    Many people feel that the company conspired with the government to undermine the regulations. It has also led to media outcry and political outrage. Sanofi – the company that manufactures Dengvaxia – was suspended by the Philippines government. Ever since the suspension there have been many social media claims spreading misinformation about the dangers of the vaccine, which are not true for those who meet the requirements to get the vaccine.   Whether a vaccine is safe or unsafe is determined in the clinical trial phases of any medication or vaccine before it is even considered for approval by a regulatory body. If, during the trials, data shows that a vaccine is unsafe or has caused harm to a patient, then the trial can be paused or suspended by the overseeing safety board.