Metro Manila (CNN Philippines, December 2) — Children administered Dengvaxia are safe from "severe disease" for two years since vaccination, the Health Secretary said Saturday in a bid to dispel parents' worries.

Citing new document from pharmaceutical company Sanofi and the World Health Organization (WHO), Health Secretary Francisco Duque III said the vaccine provides for a two-and-a-half-year protection.

"If dengue vaccination began April 2016, most likely the severe dengue manifestation will appear two and a half years henceforth," Duque told CNN Philippines.

"The parents should not be alarmed because there is still the protection," he added.

He called it a "window of opportunity" before symptoms are seen.

In 2016, the Philippines became the first Asian country to implement the use of Dengvaxia through a school-based dengue immunization program, which initially covered Grade 4 students in the National Capital Region, Central Luzon, and CALABARZON (Cavite, Laguna, Rizal, Quezon).

The Department of Health (DOH) temporarily halted its dengue vaccination program after a clinical study by Sanofi showed those not previously infected with dengue and got vaccinated with Dengvaxia could contract "severe disease."

Read more: Gov't halts dengue vaccination program due to health risk

Those at risk are some 70,000 children who were vaccinated under a Health Department program since 2016. A total of 733,713 were vaccinated, but 90 percent of them have had dengue.

Duque said the government is still trying to clarify Sanofi's definition of a "severe disease."

"We're awaiting Sanofi's definitive definition of severe disease… Magulo e there is no clarity," he said.

In the meantime, Duque is calling on parents to follow the usual dengue prevention measures, including destroying possible breeding places of mosquitoes, seeking early consultation for fever lasting more than two days, and using mosquito nets and mosquito fogging.

He also said the government is working on a master list to identify all vaccinated children, and admitted it is hard to track all 70,000 children who could be at risk.

Duque said the health department will need to increase surveillance to closely monitor the condition of the children.

The Department of Education on Saturday committed to monitor the condition of students administered with the vaccine.

In a statement Sunday, Malacañang said it will "leave no stone unturned" in holding to account those involved in the "shameless public health scam."

It also urged the public not to spread any information that may cause undue harm.

DOH urged to address 'Dengvaxia scare'

On Sunday, Vice President Leni Robredo also released a statement saying questions into the controversy surrounding Dengvaxia must be answered.

"Pinakamahalaga na magkaroon ng kasagutan kung ano iyong epekto nito, kasi iyong mga magulang ng mga batang nabakunahan... kailangan nilang malaman ano iyong kailangan nilang gawin-kung talagang mayroon itong masamang epekto, ano ba iyong puwedeng gawin para mailigtas naman iyong kanilang mga anak," she said.

[Translation: The most important thing is there must be answers its effects because the parents of children who were vaccination must know what they should do – if there really is a bad side effect, they should know what they can do to save their children.]

Robredo said they must come soon, and that those responsible be brought be made answerable.

Senator Win Gatchalian on Saturday said the DOH needs to address "the developing Dengvaxia vaccine scare" that is causing widespread panic among the parents of immunized children.

"The DOH needs to do more to stay in control of the situation," Gatchalian said in a statement.

He said local government units can be tapped to talk to the parents and "restore a sense of calm."

The government spent P3.5 billion on the immunization program, a move questioned by some doctors as Dengvaxia had not yet been approved by the World Health Organization then.

The government has fully paid Sanofi for the vaccines. Almost 800,000 doses that have not been used, amounting to almost P800 million, most of which will expire in August 2018.

Duque said the government has local and international experts studying many options to address the problem with Sanofi, adding that any move should be "evidence-based."

This story was updated on December 3 to include statements from Malacañang and Vice President Leni Robredo.