The Philippine health secretary said Monday that 136 people, mostly children, have died of measles and 8,400 others have fallen ill in an outbreak blamed partly on vaccination fears.

A massive immunization drive that started last week in hard-hit Manila and four provincial regions may contain the outbreak by April, Health Secretary Francisco Duque III said. President Rodrigo Duterte warned in a TV message Friday of fatal complications and urged children to be immunized.

"No ifs, no buts, no conditions. You just have to bring your children and trust that the vaccines ... will save your children," Duque said by telephone. "That's the absolute answer to this outbreak."

Infections spiked by more than 1,000 per cent in metropolitan Manila — the densely packed capital of more than 12 million people — in January compared to last year, health officials said.

About half of the 136 who died were children aged one to four, and many of those who perished were not inoculated, the officials said.

Vaccine hesitancy

Duque said a government information drive was helping restore public trust in the government's immunization program, which was marred in 2017 by controversy over an anti-dengue vaccine made by French drugmaker Sanofi Pasteur which some officials linked to the deaths of at least three children.

The Philippine government halted the anti-dengue immunization drive after Sanofi said a study showed the vaccine may increase the risks of severe dengue infections. More than 830,000 children were injected with the Dengvaxia vaccine under the campaign, which was launched in 2016 under then-President Benigno Aquino III. The campaign continued under Duterte until it was stopped in 2017.

Sanofi officials told Philippine congressional hearings that the Dengvaxia vaccine was safe and effective and would reduce dengue infections if the vaccination drive continued.

"It seems the faith has come back," Duque said of public trust on the government's immunization drive, citing the inoculation of about 130,000 of 450,000 people targeted for anti-measles vaccinations in metropolitan Manila in just a week.

Measles is a highly contagious respiratory disease caused by a virus which can be spread through sneezing, coughing and close personal contact. Complications include diarrhea, ear infections, pneumonia and encephalitis, or the swelling of the brain, which may lead to death.