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The Philippine government has suspended its dengue immunization program for public school students after a vaccine maker announced possible risks if the drug is administered to individuals not previously infected with dengue, Health Secretary Francisco Duque III said Friday.

"Pinahinto muna natin pansamantala lahat ng pag bakuna simula kahapon," Duque said in an interview on DZMM.

"Ipapahinto muna hanggang makakuha tayo ng recommendation from the World Health Organization... para merong technical at scientific evidence yung recommendation na ating i-implement."

The Philippines was the 1st country in Asia to approve the vaccine for individuals aged 9 and 45 years old in December 2015.

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The government has since procured P3-billion worth of Dengvaxia intended for one million public school children in areas reported to have the highest incidence of dengue in 2015: the National Capital Region, Region 3, and Region 4A. The vaccine was to be administered in three phases at 6 month intervals beginning April 2016.

Sanofi Pasteur's Wednesday statement was the first time the pharmaceutical company acknowledged that Dengvaxia should not be recommended to individuals if they have never been infected with the dengue virus. The manufacturer said it would ask health authorities to advise physicians and patients of the new information in countries where the drug has been approved.

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Duque said the DOH has asked Sanofi Pasteur to provide more details about supposed "severe reaction" that may be experienced by patients who received the vaccine.

"Gusto natin malaman ano ba ibig nila sabihin sa severe reaction. Wala kasing malinaw na paliwanag," Duque said.

The Health secretary said they are also collating the master list of all children who received the vaccine to monitor their conditions.

A total of 491,990 9-year-old students were vaccinated in the first phase, under then Health Secretary Janette Garin.

Of that number, 415,681 turned up for the second phase, which by then was implemented by Garin’s successor, Secretary Paulyn Ubial.

None of the children were ever tested to determine if they had been previously infected with the dengue virus.

“It means some of them will develop severe dengue, we don’t know who,” said independent health advocate Dr. Anthony Leachon.

“All of them will have to live with this possibility for the rest of their lives.”

Duque said about 1.4 billion units of Dengvaxia remain in stock.

The World Health Organization says as many as 400 million people are infected worldwide every year, and two-thirds are in Asia.

Scientists have long been stumped by dengue, which has four separate strains, forcing researchers to find a drug able to fight all of them at once. The deadliest form of the disease kills 22,000 people a year, the WHO says.

Dengue is now endemic in more than 100 countries. With Agence France-Presse