If the World Health Organization was hoping that its report earlier this year into the origins of COVID-19 would be the last word on the matter, it is going to be sorely disappointed. A group of 18 immunologists, biologists and other scientists have written to Science, the journal of the American Association for the Advancement of Science, to make it clear that they reject WHO’s conclusion that it is ‘extremely unlikely’ that SARS-CoV-2, the virus which causes COVID-19, entered the human population through a laboratory accident. The report, published on February 28, pretty well rejected the theory that SARS-CoV-2 could have originated as a virus held, even invented, at the Wuhan Institute of Virology, from which it escaped. It had previously been traced to a cluster of individuals infected, so it seems, at a nearby market.

A WHO team looked at the accident thesis alongside three other possibilities: that the virus jumped from directly from animal to human, that it traveled via an intermediate host, and that it entered China through imported foods from abroad. While these three possibilities were given due consideration, the laboratory accident theory was more or less dismissed.

But WHO was wrong to do so, believe the scientists, who write: ‘theories of accidental release from a lab and zoonotic spillover both remain viable’. They note that the laboratory accident theory was only considered on four of the report’s 313 pages, adding:   ‘Although there were no findings in clear support of either a natural spillover or a lab accident, the team assessed a zoonotic spillover from an intermediate host as “likely to very likely”, and a laboratory accident as “extremely unlikely.”’

The letter will put pressure on WHO to explain further why it came to the conclusion it did. While the prospect of a lab accident has been dismissed by some as a conspiracy theory, there are numerous incidents in the past of deadly viruses escaping from laboratories, including the world’s last fatal outbreak of smallpox, which occurred in a laboratory in Birmingham, England, in 1978. The Chinese government has an obvious interest in suppressing the theory that COVID has human origins, and did not help its case by at first denying the WHO team access to the Wuhan laboratory, although it did later relent.

As I wrote here in November, there are similarities between SARS-CoV-2 and a virus which was being investigated at the Wuhan laboratory. That does not prove the lab escape theory, of course, but there are very good grounds for keeping open the possibility that the COVID pandemic was not the result of random events but was a self-inflicted tragedy caused by efforts to study and understand a very similar virus.