A female Aedes aegypti mosquito c
Dengue fever, caused by the Aedes aegypti mosquito, leads to 22,000 deaths annuallyReuters

Mexico has become the first country to approve Sanofi's vaccine for dengue fever, a mosquito-borne disease that kills over 22,000 people and affects more than 400 million per year, according to the World Health Organization. The French pharmaceutical company's vaccine can be used by people aged 9 to 45 years old but not by younger children, a population considered to be most at risk. It is also not approved for use by tourists.

Sanofi, which developed the Dengvaxia vaccine over the past 20 years, said it reduces the risk of developing dengue fever by 60% in clinical trials, which experts consider less effective than desired. But COFEPRIS, Mexico's health regulator that approved the vaccine, said it could help prevent hundreds of deaths, and up to 8,000 hospital admissions, besides saving about $65m in health spending annually.

The dengue fever is transmitted to humans by the Aedes aegypti mosquito, which also spreads chikungunya, zika fever and other diseases. It has no definite or specific treatment and prevention is considered the best option.

Sanofi said it spent more than $1.6bn (£1bn; ‎€1.5bn) to develop the vaccine. Other pharmaceutical companies like Japan's Takeda and Merck are said to be developing dengue vaccines but could be at least a few years behind Sanofi.

"Results show that if you vaccinate 20% of the population in 10 endemic countries that have taken part in our phase III studies you can potentially reduce the dengue burden by 50% over a five-year period," said Guillaume Leroy, who leads the dengue team at Sanofi Pasteur, a division of Sanofi. He said the vaccine also reduces the risk of being admitted to hospital by 80% and lowers the possibility of developing the severest, hemorrhagic form of the disease by 93%

Olivier Charmeil, head of Sanofi's vaccines business, said the company aims to file for approval of the vaccine in 20 countries by the year-end. The company also expects to receive additional approvals in coming weeks, he said.

Neither Mexico nor Sanofi has revealed details of the vaccine including its price. Mexican authorities only said some 40,000 people will receive the treatment in the initial phase but did not say which parts of the country would get the drug. Deliveries of the vaccine to Mexico from a plant near Lyon, France, are to start in early 2016.