After setbacks, hope? With dengue fever expected to affect at least 5 million people and kill 5,000 in 2023, according to the World Health Organization, advances in vaccine development offer hope for significant improvements in prevention of the disease caused by the arbovirus. Spread by mosquitoes and can cause high fever, headache, nausea and vomiting.
Until recently, the short history of anti-dengue vaccination was mainly marked by the shock of Dengvaxia, a three-dose injectable vaccine launched by Sanofi in late 2015. Two years later, a French laboratory recognized that severe forms of dengue were possible. It occurs after administration of the product.
The mechanism of “facilitation of antibodies” is the main suspect of this harmful effect. To understand this, we must remember that four serotypes of dengue virus can infect the human body. A first infection with one of these serotypes triggers the production of antibodies that protect against that particular serotype, but not against others. In the event of re-infection with another serotype, it may then happen that antibodies already present in the body, poorly adapted to the newcomer or too few in number, fail to inhibit it and on the contrary increase its infectious capacity.
If Dengvaxia is injected into a person who has never had dengue fever, called a “seronegative”, it will thus play the role of first infection and prepare the ground for severe forms in the event of a subsequent infection. But, if it is administered after the first infection, it proves protective, underlines Xavier de Lambleri, head of the National Reference Center for Arboviruses: in this case, “The vaccine will awaken the immune response already there.”
Adequate tests are not reliable
Therefore, when the European Medicines Agency authorized Dengvaxia in December 2018, it recommended it only for people aged 6 to 45 years with a history of dengue infection. Vaccination campaigns respecting this indication require extensive pre-screening. However, the available tests are not reliable enough, the High Authority of Health (HAS) recalled in a framework note in September 2023, adding that they can produce false positives because they are also sensitive to other viruses. such as Zika or West Nile virus.
“Dengwexia had great potential to pave the way, but it is really difficult to use”, notes Mr. de Lambleri. This explains why “Vaccines are rarely used in practice in France”As noted, in April 2023, in the opinion of the Committee for Monitoring and Anticipation of Health Hazards (Covers).
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