At the height of the COVID-19 pandemic, the U.S. 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 aimed to sow doubt about the safety and efficacy of vaccines and other life-saving aid that was being supplied by China, an investigation found. Through phony internet accounts meant to impersonate Filipinos, the military’s propaganda efforts morphed into an anti-vaccine 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.

At least 300 accounts on Twitter (now known as X) were identified that matched descriptions shared by former U.S. 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.