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.

The French pharmaceutical expects a 100 million euro loss in the fourth quarter due to the findings from a six-year clinical trial, it said.

Sanofi said it would ask national regulatory bodies to limit or reconsider vaccine use on those who have not been previously infected with the dengue virus.

“We are working with health authorities to ensure that prescribers, vaccinators, and patients are fully informed of the new findings, with the goal of enhancing the impact of Dengvaxia in dengue-endemic countries,” said Su-Peing Ng, global medical head of Sanofi Pasteur.

Dengvaxia revenues totaled 55 million euros last year, approved in more than 10 countries for individuals older than nine years of age, according to the company.

Dengvaxia is the first vaccine to gain approval for the dengue virus, which is a mosquito-borne viral disease with no cure. The disease affects almost 4 billion people and claims around 20,000 lives each year, the company said.