Sanofi requests health authorities update information on Dengvaxia, based on new data

Duque said Dengvaxia was the first dengue vaccine to be licensed after being approved in Mexico in December 2015.

Sanofi said Thursday its dengue vaccine might worsen the disease for those who have not been previously exposed to the dengue virus, but safe for those who had a prior infection. So, when a person encounters dengue naturally after a previous vaccination, their immune system could process it as a second infection that's much more severe, according to the team from Imperial College London, Johns Hopkins Bloomberg School of Public Health and the University of Florida. It also said doctors should assess the likelihood of prior dengue infection in people before choosing whether they should get the vaccine. The vaccine is now recommended in most dengue-endemic countries for people over age nine. The mosquito-borne virus can be fatal in severe cases.

He added there were now no reports of severe dengue infection among those vaccinated.

Sanofi is proposing that national authorities update their prescribing information.

Before the current analysis, a research team past year found that the vaccine-if given to dengue-naïve individuals-"acts very much like a natural infection but without making recipients sick". He did not say whether legal action would be taken.

The new clinical data, which has been collected over a period of six years, evaluated the long-term safety and efficacy of Dengvaxia in people who had been infected with dengue prior to vaccination and those who had not. That will include mandatory history-taking of those vaccinated, mandatory reporting of all vaccine recipients admitted to hospital regardless of symptoms, and five years of post-vaccination surveillance. The company said political and economic turmoil had an effect on the launch. Dengue is different than most infectious diseases because a person's second infection is typically much more serious than the first.

The incidence of the virus has increased dramatically around the world in recent decades, with widespread outbreaks in several countries in 2016.