Online misinformation is leaching out from cheap mobile phones and free Facebook plans used by millions in the Philippines, convincing many to reject vaccinations for polio and other deadly diseases.
Childhood immunization rates have plummeted in the country -- from 87 percent in 2014 to 68 percent -- resulting in a measles epidemic and the reemergence of polio last year.
A highly politicized campaign that led to the withdrawal of dengue vaccine Dengvaxia in 2017 is widely seen as one of the main drivers of the fall.
But health experts also point to an explosion of vaccination-related misinformation that has undermined confidence in all types of immunisations.
In Tarlac City, government nurse Reeza Patriarca watched with horror the impacts of Facebook posts that falsely claimed five people had died after receiving an unspecified vaccination.
The posts, which have been shared thousands of times, went online in August, weeks after the relaunch of a World Health Organization-backed polio immunisation drive.
The Tarlac government and national health department issued statements saying no one had died, but Patriarca said the misinformation proved stronger than the truth for many parents.
"It spread like crazy. In the second week, more and more people were refusing," said Patriarca, 27, whose health unit was administering the vaccine across nine neighborhoods.
"Some believed the (government) explanation, others didn't. We couldn't force them."
The false report in Tarlac even deterred people from getting free flu jabs in the nearby city of San Jose del Monte.
Health worker Rosanna Robianes said elderly people who would normally queue at her center for their shot did not show up.
"They said it's because of Facebook, that there's a report that people who had been vaccinated in Tarlac had died," she said.
Toxic to humans
Interest in online anti-vaccine content has surged during the pandemic as scientists around the world have raced to develop an effective inoculation.
The number of followers of anti-vaccine groups and pages on Facebook in the Philippines has risen by 190,000 to around 500,000, according to social media monitoring platform CrowdTangle's latest data.
The pages have attracted eight million interactions -- reactions, comments and shares -- since the pandemic began.
April Villa, a 40-year-old mother of two from the northern province of Laguna, is part of the anti-vaxxer movement.
Villa follows the Facebook group "NO TO VACCINE - PHILIPPINES", which was created in July and has more than 2,000 members.
She said she joined the group to access "information which our education system could never teach".
"It's toxic to the human body, it kills the natural antibodies," Villa told AFP, explaining her views on vaccines, adding she would refuse a Covid-19 shot if one became available.
Most of the Philippines' 73 million internet users have a Facebook account, according to Britain-based media consultancy We Are Social.
Nearly all of them access the site on their mobile phones, where Facebook offers free data to access a limited version of its platform and other selected websites.
Many poorer Filipinos rely on Facebook's Free Basics plan to use the internet, trapping them in the social media giant's information bubble.
Facebook chief executive Mark Zuckerberg has defended the service, saying it gives people who could not otherwise afford it an opportunity to use the internet.
Posts about President Rodrigo Duterte flooded Facebook in 2016 and were seen as playing a key role in his election victory -- and officials say the site has been a boon for anti-vaxxer groups too.
Wilda Silva, the health department's immunisation program manager, said fake news about vaccines "travels faster and wider than correct information".
"Once you tap that fear factor, people's minds quickly change and the fear stays long in their minds," said Silva, who worries there may be a big outbreak of preventable diseases next year.
Public fears could also affect the take-up of a COVID-19 vaccine -- even among people who support inoculations -- in a country facing the highest infection rates in Southeast Asia.
"I trust vaccines 100 percent," said Jett Bucho, from a poor neighbourhood of San Jose del Monte, after her one-year-old daughter was immunised against polio.
But the 26-year-old said online conspiracy theories that a coronavirus vaccine could be used to implant chips and control humans had planted a seed of doubt in her mind.
"On Facebook, if you keep scrolling, you see this," she said.