Ever since Chinese President Xi Jinping’s government quashed a COVID-19 outbreak in the central city of Wuhan roughly two years ago, it has repeatedly sought to blame virus outbreaks on foreign sources. The latest target is international mail.

Worries surged in China last week that overseas parcels could be tainted with coronavirus still potent enough to infect those who came into contact with it. It began with officials saying Beijing’s first omicron infection was a woman who handled a letter from Canada. That led local officials in the southern city of Guangzhou to order all residents who got overseas mail over a four-day period to get tested, and the State Post Bureau to warn people to be extra careful with parcels.

Social-media users immediately began to ridicule the theory, with one doctor writing on the Twitter-like Weibo service that it would become an international joke. The post later disappeared from the doctor’s verified account. Thousands of netizens liked another lengthy missive on a popular verified account belonging to a virologist who explained the science behind why the virus was extremely unlikely to spread via international mail.