The WHO suggested the vaccine be used only among people who have had dengue infection before.
Sanofi, whose shares rose 0.4 percent in Paris on Monday, explained its "new findings" of increased risk at a news conference in Manila. This is also a vaccine intended for millions of people around the world, and the safety bar is typically set high.
"The WHO position paper did not include a recommendation to countries to introduce the dengue vaccine into their national immunization programs".
However, the World Health Organization said in a July 2016 research paper that "vaccination may be ineffective or may theoretically even increase the future risk of hospitalized or severe dengue illness in those who are seronegative at the time of first vaccination regardless of age".
The Philippine government last week suspended its dengue immunization program for public school students after French drugmaker Sanofi announced possible risks if the Dengvaxia is administered to individuals not previously infected with dengue.
Pharmaceutical giant Sanofi Pasteur launched Dengvaxia as a vaccine against the mosquito-borne viral disease that infects an average of 390 million people worldwide every year.
Last week, the Philippines' health department suspended the vaccination after Sanofi announced evidence showing that people who receive the vaccine, known as Dengvaxia, without previous dengue infection could face the risk of their disease worsening. It does not know how many people have received the vaccine in Brazil since its 2015 approval.
Former Health Secretary Janette Garin, who implemented the program under the administration of then-President Benigno Aquino, said she welcomed the investigation.
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. Since a year ago, 733,713 children have been vaccinated by the Department of Health in Metro Manila, Central Luzon and Calabarzon.
"When we evaluated the clinical records, it was not related to the dengue vaccination", Bayugo said.
Given the recent developments, the WHO Country Office said it is now waiting for "expert analysis of new data and advice" on the use of Dengvaxia.
While Sanofi's Dengvaxia is the first-ever approved vaccine for dengue, scientists already recognized it was not flawless and did not protect equally against the four different types of the virus in clinical tests.