At the height of the Covid-19 pandemic, the US military launched a secret campaign to counter what it perceived as China’s growing influence in the Philippines, a nation hit especially hard by the deadly virus.

The clandestine operation has not been previously reported. It aimed to sow doubt about the safety and efficacy of vaccines and other life-saving aid that was being supplied by China, a Reuters investigation found. Through phony internet accounts meant to impersonate Filipinos, the military’s propaganda efforts morphed into an anti-vax campaign. Social media posts decried the quality of face masks, test kits and the first vaccine that would become available in the Philippines – China’s Sinovac inoculation.

Reuters identified at least 300 accounts on X, formerly Twitter, that matched descriptions shared by former US military officials familiar with the Philippines operation. Almost all were created in the summer of 2020 and centered on the slogan #Chinaangvirus – Tagalog for China is the virus.

This post, identified by Reuters, matched the messaging, timeframe and design of the US military’s anti-vax propaganda campaign in the Philippines, former and current military officials say. Social media platform X also identified the account as fake and removed it.

(Beneath the message is a picture of then-Philippines President Rodrigo Duterte saying: “China! Prioritise us first please. I’ll give you more islands, POGO and black sand.” POGO refers to Philippine Offshore Gaming Operators, online gambling companies that boomed during Duterte’s administration. Black sand refers to a type of mining.)

“Covid came from China and the VACCINE also came from China, don’t trust China!” one typical tweet from July 2020 read in Tagalog. The words were next to a photo of a syringe beside a Chinese flag and a soaring chart of infections. Another post read: “From China – PPE, Face Mask, Vaccine: FAKE. But the Coronavirus is real.”

After Reuters asked X about the accounts, the social media company removed the profiles, determining they were part of a coordinated bot campaign based on activity patterns and internal data.

The US military’s anti-vax effort began in the spring of 2020 and expanded beyond Southeast Asia before it was terminated in mid-2021, Reuters determined. Tailoring the propaganda campaign to local audiences across Central Asia and the Middle East, the Pentagon used a combination of fake social media accounts on multiple platforms to spread fear of China’s vaccines among Muslims at a time when the virus was killing tens of thousands of people each day.

A key part of the strategy: amplify the disputed contention that, because vaccines sometimes contain pork gelatin, China’s shots could be considered forbidden under Islamic law.

The military programme started under former President Donald Trump and continued months into Joe Biden’s presidency, Reuters found, even after alarmed social media executives warned the new administration that the Pentagon had been trafficking in Covid misinformation. The Biden White House issued an edict in spring 2021 banning the anti-vax effort, which also disparaged vaccines produced by other rivals and the Pentagon initiated an internal review, Reuters found.

“I don’t think it’s defensible. I’m extremely dismayed, disappointed and disillusioned to hear that the US government would do that.”

Daniel Lucey, infectious disease specialist at Dartmouth’s Geisel School of Medicine. The US military is prohibited from targeting Americans with propaganda, and Reuters found no evidence the Pentagon’s influence operation did so.

Spokespeople for Trump and Biden did not respond to requests for comment on the clandestine programme.

A senior Defence Department official acknowledged the US military engaged in secret propaganda to disparage China’s vaccine in the developing world but the official declined to provide details.

A Pentagon spokeswoman said the US military “uses a variety of platforms, including social media, to counter those malign influence attacks aimed at the US, allies and partners.” She also noted that China had started a “disinformation campaign to falsely blame the United States for the spread of Covid-19.”

In an email, the Chinese Ministry of Foreign Affairs said that it has long maintained the US government manipulates social media and spreads misinformation.

Manila’s embassy in Washington did not respond to Reuters inquiries, including whether it had been aware of the Pentagon operation. A spokesperson for the Philippines Department of Health, however, said the “findings by Reuters deserve to be investigated and heard by the appropriate authorities of the involved countries.” Some aid workers in the Philippines, when told of the US military propaganda effort by Reuters, expressed outrage.

Briefed on the Pentagon’s secret anti-vax campaign by Reuters, some American public health experts also condemned the programme, saying it put civilians in jeopardy for potential geopolitical gain. An operation meant to win hearts and minds endangered lives, they said.

“I don’t think it’s defensible,” said Daniel Lucey, an infectious disease specialist at Dartmouth’s Geisel School of Medicine. “I’m extremely dismayed, disappointed and disillusioned to hear that the US government would do that,” said Lucey, a former military physician who assisted in the response to the 2001 anthrax attacks.

The effort to stoke fear about Chinese inoculations risked undermining overall public trust in government health initiatives, including US-made vaccines that became available later, Lucey and others said. Although the Chinese vaccines were found to be less effective than the American-led shots by Pfizer and Moderna, all were approved by the World Health Organization. Sinovac did not respond to a request for comment.

Health workers and the government struggled to get Filipinos vaccinated against COVID-19, despite mobile sites like this one, operating in May 2021 in Taguig, Metro Manila, Philippines. At that time, the Philippines had one of the worst inoculation rates in Southeast Asia. The primary vaccine available then was Sinovac. REUTERS/Lisa Marie David

Academic research published recently has shown that, when individuals develop scepticism toward a single vaccine, those doubts often lead to uncertainty about other inoculations. Lucey and other health experts say they saw such a scenario play out in Pakistan, where the Central Intelligence Agency used a fake hepatitis vaccination programme in Abbottabad as cover to hunt for Osama bin Laden, the terrorist mastermind behind the attacks of September 11, 2001.

Discovery of the ruse led to a backlash against an unrelated polio vaccination campaign, including attacks on healthcare workers, contributing to the reemergence of the deadly disease in the country.

“It should have been in our interest to get as much vaccine in people’s arms as possible,” said Greg Treverton, former chairman of the US National Intelligence Council, which coordinates the analysis and strategy of Washington’s many spy agencies. What the Pentagon did, Treverton said, “crosses a line.”

Together, the phony accounts used by the military had tens of thousands of followers during the programme. It was not determine how widely the anti-vax material and other Pentagon-planted disinformation was viewed or to what extent the posts may have caused Covid deaths by dissuading people from getting vaccinated.

In the wake of the US propaganda efforts, however, then-Philippines President Rodrigo Duterte had grown so dismayed by how few Filipinos were willing to be inoculated that he threatened to arrest people who refused vaccinations.

“You choose, vaccine or I will have you jailed,” a masked Duterte said in a televised address in June 2021. “There is a crisis in this country … I’m just exasperated by Filipinos not heeding the government.”

Then-Philippines President Rodrigo Duterte pleaded with citizens to get the COVID vaccine. “You choose, vaccine or I will have you jailed,” a masked Duterte said in this televised address in June 2021.

When he addressed the vaccination issue, the Philippines had among the worst inoculation rates in Southeast Asia. Only 2.1 million of its 114 million citizens were fully vaccinated – far short of the government’s target of 70 million. By the time Duterte spoke, Covid cases exceeded 1.3 million and almost 24,000 Filipinos had died from the virus. The difficulty in vaccinating the population contributed to the worst death rate in the region.

A spokesperson for Duterte did not make the former president available for an interview.

Some Filipino healthcare professionals and former officials contacted were shocked by the US anti-vax effort, which they say exploited an already vulnerable citizenry. Public concerns about a Dengue fever vaccine, rolled out in the Philippines in 2016, had led to broad scepticism toward inoculations overall, said Lulu Bravo, executive director of the Philippine Foundation for Vaccination. The Pentagon campaign preyed on those fears.

“Why did you do it when people were dying? We were desperate,” said Dr Nina Castillo-Carandang, a former advisor to the World Health Organization and Philippines government during the pandemic. “We don’t have our own vaccine capacity,” she noted, and the US propaganda effort “contributed even more salt into the wound.”

The campaign also reinforced what one former health secretary called a longstanding suspicion of China, most recently because of aggressive behaviour by Beijing in disputed areas of the South China Sea. Filipinos were unwilling to trust China’s Sinovac, which first became available in the country in March 2021, said Esperanza Cabral, who served as health secretary under President Gloria Macapagal Arroyo. Cabral said she had been unaware of the US military’s secret operation.

“I’m sure that there are lots of people who died from Covid who did not need to die from Covid,” she said.

To implement the anti-vax campaign, the Defence Department overrode strong objections from top US diplomats in Southeast Asia at the time, it was found. Sources involved in its planning and execution say the Pentagon, which ran the programme through the military’s psychological operations centre in Tampa, Florida, disregarded the collateral impact that such propaganda may have on innocent Filipinos.

“We weren’t looking at this from a public health perspective,” said a senior military officer involved in the program. “We were looking at how we could drag China through the mud.”

As the Covid pandemic swept through the Philippines, a man lit a candle atop a tomb in a flooded cemetery there in October 2021. Many citizens were hesitant to be vaccinated.

• A Reuters report