Since infecting its first victims in the central Chinese city in late 2019, the pathogen has afflicted almost every country in the world, killing more than 3.4 million people and pummelling national economies.
Beijing has always denied any claims that Covid-19 could have escaped from one of its laboratories.
Citing a US intelligence report, the Wall Street Journal reported Sunday that the three people from the Wuhan Institute of Virology were affected as early as November 2019, suffering from "symptoms consistent with both Covid-19 and common seasonal illness".
Fact Checker | Timeline: How the Wuhan lab-leak theory suddenly became credible https://t.co/rA8oJbQajT
— The Washington Post (@washingtonpost) May 25, 2021
Wuhan laboratory claims "zero infection" record of staff
China disclosed the existence of an outbreak of pneumonia in Wuhan to the World Health Organization on 31 December, 2019.
Asked about the reports on Monday, Foreign Ministry spokesman Zhao Lijian described them as "totally untrue".
He told reporters that, according to a statement from the institute, it "had not been exposed to Covid-19 before 30 December 2019, and a "zero-infection" record has been maintained among its staff and graduate students so far.
The coronavirus was, however, taken to the lab for study, according to Chinese authorities.
- WHO report says animals likeliest origin of Covid-19, minimises lab hypothesis
- Wuhan lab boss says 'no way coronavirus came from us'
Conspiracy suspicions
The theory that the killer virus leaked from a Chinese lab was fuelled by, among others, the administration of former US president Donald Trump.
Last March, after a four-week stay in Wuhan, a joint study by the WHO and Chinese experts deemed such an explanation "extremely unlikely".
Experts favour the generally accepted theory of the natural transmission of the virus from an animal -- probably a bat -- to humans, through another animal that has not yet been identified.
Some believe, however, that WHO specialists did not have enough freedom to work unhindered during their investigation in Wuhan.
