April 20 (UPI) -- The World Health Organization is recommending that a vaccine against dengue should only be used on people who have previously been infected with the mosquito-spread disease.
On Thursday, WHO's Strategic Advisory Group of Experts on Immunization made the changes after two days of meetings in Geneva, Switzerland. In July 2016, the group recommended Dengvaxia only be given to individuals 9 years or older in endemic regions.
Last November, Sanofi Pasteur, the France-based drugmaker, recommended restricting Dengvaxia's use to people previously infected. In studies, people given the vaccine without a previous infection before can become vulnerable to a severe reaction if they are later infected.
Use of of the vaccine, which was first licensed in December 2015, likely will be diminished because no rapid, reliable test for previous dengue infection is available.
"It is for the company to decide how they cope with this," advisory group chairman Alejandro Cravioto of the National Autonomous University of Mexico in Mexico City said at a news conference.
Sanofi Pasteur said in a statement: "We are confident in Dengvaxia's safety and its proven potential to reduce dengue disease burden in endemic countries.
"At Sanofi, we have worked to provide an innovative vaccine against dengue in spite of the challenges posed by this complex infection.
The company added it plans to "continue to work with the international public health community and endemic countries, to ensure the best usage of the vaccine to increase protection for populations at risk of subsequent dengue infections, potentially more debilitating."
Dengue is spread by mosquitoes that bite during the daytime and the disease spreads rapidly during the rainy season.
WHO estimates there are 50 million to 100 million cases 20,000 deaths annually, mainly in Southeast Asia and the Western Pacific regions. In all, 2.5 billion people, 40 percent of the world's population, are at risk.
WHO said Dengvaxia has been introduced in two subnational programs in the Philippines and Brazil, targeting about a million individuals. It is also available on the private market.
WHO said the screening option was preferred over "population seroprevalence criteria," which is blood testing of all individuals.
"For countries considering vaccination as part of their dengue control program, a 'pre-vaccination screening strategy' would be the preferred option, in which only dengue-seropositive persons are vaccinated," WHO said in a release.
Last December, researchers at Stanford said they conducted tests that prove a new drug called NGI-1 is capable of shutting down flaviviruses, the family that includes mosquito-borne viruses like Zika, dengue and West Nile. They cut off access to key proteins in mammalian cells that invading viruses rely on.
Also last year, scientists at Johns Hopkins said they have created mosquitoes resistant to the dengue virus, which might eventually help control the spread of the disease in humans. They genetically modified Aedes aegypti mosquitoes to boost their natural ability to fight infection by the virus.