Singapore's health authority issued advisory asking professionals not to administer a dengue vaccine to patients who have not been previously infected by the virus.
New analysis of long-term studies shows that for those who never had dengue, vaccination with Dengvaxia can lead to more severe disease.
Singapore's Health Sciences Authority (HSA) last week confirmed an arlier assessment that there is a postulated risk of a higher incidence of severe dengue following vaccination in individuals who do not have previous dengue infection.
The Paris-based drugmaker last week asked regulators to update the vaccine's label so doctors avoid injecting patients who have never suffered a bout of the mosquito-borne illness.
The world's first dengue vaccine, sold in countries from Thailand to Brazil, is forecast by analysts to generate about $340 million in sales in 2020, down from earlier estimates of $840 million.
HSA said it is now working with Sanofi to strengthen the package insert to include the warning of an increased risk of hospitalisation for dengue and clinically severe dengue in vaccinated individuals not previously infected by dengue.