Amid mounting public concern, Sanofi explained its "new findings" at a news conference in Manila but did not say why action was not taken after a World Health Organization report in mid-2016 that identified the risk it was now flagging.
With the vaccine now widely available, the Philippines health authority rushed to vaccinate almost 734,000 children, as part of a program that cost the government 3.5 billion pesos.
One 12-year old girl in Tarlac province, north of the capital Manila, who completed the three-dose vaccine treatment, showed symptoms of severe dengue, Health Undersecretary Gerardo Bayugo told Reuters by phone.
Philippine health officials have ordered Sanofi to jerk its dengue vaccine off the market as the controversy over the health threat it poses to children continues to roil the country.
The Philippines Department of Health halted use of Dengvaxia last week after Sanofi reported it could worsen the disease in some people.
Sanofi officials said on Monday in Manila that there had been no reported deaths related to the vaccine which was used to immunize almost 734,000 children aged 9 and over in the Philippines. People in warm countries including the Philippines face the highest risk.
The safety fears involve possible increased risk to people who had not previously been exposed to the dengue virus prior to vaccination with Dengvaxia.
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Singapore's Health Sciences Authority said last week that it flagged risks when Dengvaxia was approved there in October 2016, and was working with Sanofi to strengthen risk warnings on the drug's packaging.
The vaccine so far has been approved in 19 countries and launched in 11, Sanofi said.
The vaccine, given to anyone who had not already been infected, left people vulnerable to severe, life-threatening dengue in the event they were subsequently infected by wild type dengue.
"All drug establishments, including consumers and non-consumer user (e.g. healthcare professionals) are enjoined to take part in the post-marketing surveillance of Dengvaxia, by reporting to FDA any incident that reasonably indicates that Dengvaxia has caused or contributed to the death, serious illness, or serious injury to a consumer, a patient, or any person", the FDA said in a statement.
Anvisa did not immediately respond to a request for comment.
Sanofi, whose shares rose 0.4 percent in Paris on Monday, explained its "new findings" of increased risk at a news conference in Manila.
A spokesman for Philippines President Rodrigo Duterte said on Sunday the government would hold to account those responsible for the program. In severe cases, dengue can cause breathing problems, hemorrhaging and organ failure. But noted dengue expert Scott Halstead - who has spent decades in the field - says that Sanofi's researchers never fully learned the biology of the disease they were trying to eradicate, pointing them straight to the crisis they're in now.