Q Why is the Wuhan laboratory a focus of interest?

A The Wuhan Institute of Virology (WIV) is a high-security research facility that studies pathogens in nature with the potential to infect humans with deadly new diseases.

The lab has done extensive work on bat-borne viruses since the 2002 Sars-CoV-1 global outbreak. The search for its origins led to the discovery of Sars-like viruses in a bat cave in south-west China.

The institute's researchers experiment with live viruses in animals to gauge human susceptibility. To reduce the risk of pathogens escaping, the facility is supposed to enforce rigorous safety protocols. But even the strictest measures cannot eliminate such risks.

Q Why do some scientists suspect a laboratory accident?

A To some scientists, the release of a dangerous pathogen via a careless lab worker is a plausible hypothesis for how the pandemic started.

The Wuhan lab is not far from the Huanan Seafood Market, the site of the first known Covid-19 superspreader event. Their proximity raised suspicions, fuelled by the failure to identify any wildlife infected with the same viral lineage, and compounded by Beijing's refusal to allow the lab-leak scenario to be fully investigated.

Although the Wuhan lab's scientists have said they had no trace of Sars-CoV-2 in their inventory at the time, 24 researchers have sent a letter to the World Health Organisation (WHO) urging a rigorous, independent investigation. The WHO's first such mission to China this year failed to probe deeply enough, they wrote.

A US State Department fact sheet had alleged, without proof, that several WIV researchers had fallen sick with symptoms consistent with Covid-19 before the first confirmed case in December 2019.

Q What are the arguments for animal-to-human transmission?

A Many scientists believe a natural origin is more likely and have seen no scientific evidence to support the lab-leak theory.

Professor Kristian G. Andersen, a scientist at Scripps Research who has done extensive work on pathogens transmissible from animals to humans, said similar genomic sequences occur naturally in coronaviruses and are unlikely to be manipulated.

Q Has new information emerged to lend credence to one theory over another?

A The scientists' March 4 letter to the WHO refocused attention on the lab-leak scenario, but offered no new evidence. Nor has definitive proof of a natural origin surfaced.

US President Joe Biden said on Wednesday that his national security staff do not believe there is sufficient information to assess one theory to be more likely than another.

REUTERS