China began censoring online discussions on the new coronavirus weeks before officially acknowledging the scope of the disease, according to a report published Tuesday.

Although Chinese authorities did not publicly acknowledge the severity of the virus until January 20, censorship began as early as December 31, said researchers at the University of Toronto’s Citizen Lab.

Even general terms such as “unknown Wuhan pneumonia” and “Wuhan Health Commission” were deemed taboo in the early weeks of the epidemic, said the report.

More than 3,100 people have died and over 90,000 have been infected worldwide by the virus.

Citizen Lab said its research showed at least one social media platform in China was blocking some virus content three weeks before the government confirmed it was spreading between people.

That “strongly suggests that social media companies came under government pressure to censor information at early stages of the outbreak,” the report said.

In China it is common for social media companies to scrub content considered politically sensitive, including protests and government criticism.

From the end of December to mid-February, Citizen Lab found more than 500 blocked keywords and phrases on WeChat — which has over one billion active monthly users — as well as on live-streaming platform YY.

Some censored terms referred to information that was later made official, such as the fact that the virus was contagious.

The two apps also censored a broad range of keywords, including factual information.

For instance, messages that included the words “pneumonia”, “disease control and prevention”, “virus”, and “medical journal” were censored when Citizen Lab tested WeChat on February 14.

“What makes this case unique is the potential public health harm blocking this information may have,” said Lotus Ruan, researcher at Citizen Lab, commenting on the broad scope of censorship.

Doing so can “limit (the) public’s ability to be informed and protect themselves,” she told AFP.

Though the death of a whistleblowing doctor prompted rare calls for political reform in February, Beijing has doubled down on censorship.

In early February China’s cyberspace authority said it would “supervise” the country’s largest social media firms on virus-related content.

And Chinese President Xi Jinping called for even tighter control over online discussion to ensure “positive energy” and social stability.

“So far Beijing seems to draw the wrong conclusion from the crisis, that it needs to repress more, not less,” said Lokman Tsui, a communications professor at the Chinese University of Hong Kong.