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 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 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.