According to a new 120-page report from the World Health Organization, the novel coronavirus likely spread to humans from an animal. But experts say the topic requires more study. The new report also says the disease likely started to spread amongst humans no more than a month or two before it was identified in December of 2019. 

As for the source of the infections, no conclusive answer has been found as of yet, but the following possibilities were listed in order of likelihood, according to the international team of investigators:

• Direct zoonotic spillover is considered to be a possible-to-likely pathway; 
• Introduction through an intermediate host is considered to be a likely to very likely pathway; 
• Introduction through cold/ food chain products is considered a possible pathway; 
• Introduction through a laboratory incident was considered to be an extremely unlikely pathway. 

In regard to the lab incident hypothesis, which has received significant news coverage, WHO investigators found this scenario to be extremely unlikely for several reasons. Excerpted from the WHO report:

• The closest relatives of SARS-CoV-2 from bats and pangolin are evolutionarily distant from SARS- CoV-2 in humans.
• There is no record of viruses closely related to SARS-CoV-2 in any laboratory before December 2019. 
• The three laboratories in Wuhan working with either CoVs diagnostics and/or CoVs isolation and vaccine development all had high quality biosafety level (BSL3 or 4) facilities that were well-managed, with a staff health monitoring program. There was no reporting of COVID-19 compatible respiratory illness from these monitoring programs during the weeks/months prior to December 2019, and no serological evidence of infection in workers through SARS-CoV-2-specific serology-screening.

Note: WHO investigators did not consider the hypothesis of deliberate release or deliberate bioengineering of SARS-CoV-2 for release due to the fact that geneticists had previously ruled that scenario out upon analysis of the SARS-CoV-2 genome.

“This report is a very important beginning, but it is not the end,” said WHO Director-General Tedros Adhanom Ghebreyesus. “We have not yet found the source of the virus, and we must continue to follow the science and leave no stone unturned as we do.”

ADDITIONAL INFO

Full WHO Report

Origins of the SARS-CoV-2 virus

WHO Press Release 

WHO calls for further studies, data on origin of SARS-CoV-2 virus, reiterates that all hypotheses remain open