Some new claims emerged this week from a Chinese medical expert who fled to the US that the Covid-19 pandemic began in a military lab and was covered up by Chinese officials. Commentators have already raised serious doubts. It's not the first time theories have surfaced the SARS-CoV-2 was lab-made, despite overwhelming scientific evidence to the contrary. How much stock should we place in them? Herald science reporter Jamie Morton asked Massey University's Professor David Hayman, one of the world's leading experts in infectious disease ecology.

Where do these claims seem to be coming from and what is driving them?

I think people are searching for an explanation and meaning when they see how bad this pandemic has been and a problem with disease emergence events is we nearly never know immediately how they start, even if that becomes more clear with time.

However, the World Health Organisation (WHO) and United Nations have called the situation an "infodemic" and highlighted that people are using the situation to increase distrust, sell fake cures, or even as a method for an online cyberattack.

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What makes these new claims by Dr Li Meng-Yan different? And do you see any obvious red flags here?

This newest claim is slightly different because the supposed whistle-blower has at least worked with viruses and for a short period in a very good lab [at the time of the outbreak, Meng-Yan was employed at the Hong Kong School of Public Health at Hong Kong University, however the university has denied she'd never undertaken research on human-to-human transmission of the virus].

Similarly, some of the claims are more plausible than before.

For example, it is feasible that the Chinese government had evidence of human-to-human transmission prior to it being announced and didn't want to share this and while early evidence focused on the market as a source, later information released has suggested that while there may have been some virus there, it's not clear if there was animal to human or human to human transmission there.

What seems harder to believe is that she has evidence that this was a covered-up escape from a lab, though that is the most plausible of all the many conspiracy theory out there.

One reason it is harder to believe, beyond the science, is because she was based in Hong Kong at the time and the laboratory she worked in is a world-renowned lab, with the lead researchers frequently publishing on coronaviruses influenza viruses in people and domestic and wild animals.

The Hong Kong university has simply made a clear statement that there is no basis for her claims, including that she wasn't working on the particular project she claims.

The group includes a virologist who co-authored the first paper making the diagnostic test to detect the virus available to the whole world for free.

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"Frankly, it would be incredible if this were not a naturally occurring virus that came from wildlife," says Massey University's Professor David Hayman. Photo / Supplied

There are some red flags, for example, given the US administration's rhetoric towards China, appearing on Fox News to make a claim when seeking asylum in the US is probably a good strategic move and Fox News has been a platform for misinformation and lies about Covid-19.

However, again this is complicated, not least by the recent China-Hong Kong relationship and China's poor record on free speech and human rights.

Why are scientists sure that SARS-CoV-2 came from animals, or evolved naturally. What does the science tell us - and can we say it's effectively settled?

The first Sars outbreak led to a huge effort to find the wildlife hosts of Sars-related viruses. Since then, virologists have discovered several hundred different coronaviruses in bats, from all over the world, including New Zealand.

It's really clear that while birds are natural hosts to a range of coronaviruses, bats are the natural and ancestral hosts to the viruses related to SARS-CoV-1, the original, and SARS-CoV-2, the cause of Covid-19.

Not only that, but Sars-related coronaviruses from Chinese bats have been discovered that can already infect human cells without any additional mutations and related viruses have been discovered in pigs and bats after an outbreak of disease in pigs that killed around 25,000 pigs.

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The viruses were found in bats in the same location as the pigs, repeatedly over a three-year period. So, it is clear that not only are these viruses ubiquitous in nature, but also that have and do emerge naturally.

Regarding the specific SARS-CoV-2, it is new, but not so dissimilar to other Sars-related coronaviruses.

In fact, some people have recently used what are called molecular clocks to analyse the genomes to estimate it shared a common ancestor to the other known bats between around 1948 to 1982.

Nothing closer has been reported in any publications from any viral collection to date.

Lastly, we have evidence from other studies, showing that other viruses are infecting people intermittently, but regularly, around the world.

Together we have a huge weight of evidence to suggest this is a naturally occurring virus.

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The details of how and when it first infected someone, and from what species, are still not clear. This causes people frustration, but it's actually normal.

For example, after more than 40 years since its discovery, we still haven't fully isolated an outbreak-related Ebola virus from bats, but we have a huge amount of evidence to say they are the natural hosts in Africa.

Frankly, it would be incredible if this were not a naturally occurring virus that came from wildlife.

What is it you think that people should consider when they read about such claims? What questions should they ask when assessing their validity?

It depends on the claims. We genuinely have to keep an open mind - for example, I can't prove here that SARS-CoV definitely didn't escape from a secret experiment - but knowing the science after more then a decade of studying these viruses and looking at all the evidence it seems overwhelmingly like this is just another very unfortunate emerging virus.

One, it is worth remembering, which people initially praised the Chinese government for controlling.

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There are other claims, however, that are simply impossible, dangerous, or can be disproved through careful robust studies, such as different treatments for Covid-19.

The key for people outside the field is to keep listening to informed commentators - but to also be aware that evidence can and does change, and this is the way science works.