New York - A dengue fever vaccine developed by the French pharmaceutical giant Sanofi has been approved for use by Mexico, the first approval in the world for any vaccine for the disease, which afflicts tens of millions of people around the world and is becoming an increasing threat.

Sanofi said in a news release Wednesday that the vaccine, which it is calling Dengvaxia, was approved by Mexico's Federal Commission for the Protection against Sanitary Risk for prevention of dengue in people 9 to 45 years old living in endemic areas.

"We are making dengue the next vaccine-preventable disease," Olivier Charmeil, executive vice president for vaccines at Sanofi, said in an interview.

But it is still uncertain how widely the vaccine will be deployed, both in Mexico and other countries, because of limits to its effectiveness and national budgets.

In clinical trials, the vaccine reduced the risk of developing dengue by about 60 percent, which some experts have said is less effective than desired. The vaccine seems least effective in children younger than 9, particularly those younger than 6, and may even increase their risk of having more severe disease in the long run, according to a longer term follow-up from the clinical trials.

Mr. Charmeil said the vaccine would be available early next year in Mexico for people who want to buy it for themselves, though the price has not yet been announced. But much greater use would come if the government decides to deploy a public vaccination campaign. The government has not decided what to do yet.