China is under pressure from countries across the world to allow the World Health Organization to conduct a second study on the origin of SARS-CoV-2, the virus that causes COVID-19. Over the past few weeks, statements from the White House and the G7 have spurred renewed interest on how the virus may have developed. Divya Rajagopal breaks down the various theories, including one that suggests the virus escaped from a Wuhan laboratory.
What are world leaders asking for?
Last week, G7 leaders called for a timely, transparent, expert-led, and science-based, second origin study in China led by the WHO.
The recommendation for the second study on the origin of SARS-CoV-2 came from an international multidisciplinary team of experts selected by WHO, which visited China this year and worked with Chinese experts to understand how the virus might have been introduced.
US President Joe Biden announced a formal investigation into the origin of the virus in May and gave US intelligence agencies 90 days to collect information that “could bring us closer to a definitive conclusion.”
“The United States will also keep working with like-minded partners around the world to press China to participate in a full, transparent, evidence-based international investigation and to provide access to all relevant data and evidence,” Biden said in a statement in May.
What did the WHO team report say?
The team set up as part of the WHO-convened Global Study of Origins of SARS-CoV-2 consisted of 17 Chinese members and 17 experts from other countries and the World Organisation for Animal Health and WHO. The team was jointly headed by Peter Ben Embarek, an expert in zoonoses (infectious diseases that jump from animals to humans) from Denmark, and Prof Liang Wannian from Tsinghua University in Beijing.
After conducting their study from January 14 to February 10, 2021, in Wuhan, including a 14-day quarantine, they presented their findings in March. The team collected more than 80,000 wildlife, livestock and poultry samples from 31 provinces in China, but no positive result was identified for SARS-CoV-2 antibodies. After extensive testing of animal products in Huanan Seafood Wholesale Market, no evidence of animal infections was found.
The team said there were four possible pathways for the introduction of the virus, each with varying degrees of plausibility.
1) Introduction through an intermediate host: The scientists concluded that this was considered to be a likely to very likely pathway of transmission. It is possible that domesticated wild animals commonly sold in the markets at Huanan, Wuhan, including pangolins, could have been the intermediate hosts that transmitted the virus to humans.
2) Direct transmission: Direct transmission from animals to humans is a theory that the scientists thought had merit, assessing it as possible to likely. The possibility of the disease originating through the animal market came from investigations that found the Huanan wet market had witnessed infection of SARS-CoV-2. Yet, the scientists said the source of this contamination could not be determined.
3) Introduction through cold/food supply chain: Huanan market was home to cold chain and animal products from over 20 countries. A random sampling found the virus on the packaging of products. However, since surface transmission has been conclusively ruled out as a route of infection, the cold/food supply chain theory remains weak. The team concluded that the potential for SARS-CoV-2 introduction via cold/food chain products could be considered possible.
4) Introduction through a laboratory incident: The lab leak theory is the most debated one, although the study team assessed it as extremely unlikely. The idea that the virus was a biological weapon and “escaped” from a lab comes from several conjectures. One of them was that the Wuhan Institute of Virology is located near the Huanan market and a possible accident led the virus to slip out of the lab.
However, the team noted that there has been no record of viruses with a genomic structure similar to the COVID-19 virus before December 2019.
“Regarding accidental culture, prior to December 2019, there is no evidence of circulation of SARS-CoV-2 among people globally and the surveillance program in place was limited regarding the number of samples processed and therefore the risk of accidental culturing SARS-CoV-2 in the laboratory is extremely low,” the investigators wrote in their 120-page report.
They added that lab workers who were tested before December 2019 had no prevalence of antibodies related to SARS-CoV-2.
What happens next?
If China agrees, the second round of investigation will focus on access to raw data. WHO Director-General Tedros Adhanom Ghebreyesus said in March this year that the team faced difficulties in accessing raw data. A collaborative study with comprehensive data sharing is one of the demands of WHO and other countries.
Another area of investigation will be tracing the animals sold in the markets in and around Wuhan to understand potential animal hosts and intermediaries. The expert panel of WHO’s origin study has recommended studies to find out the earliest human cases and clusters. It is speculated that China reported the disease outbreak in December 2019, but the infection may have erupted in September 2019.
The role of domesticated wild animal trade in Wuhan is another area of study that is recommended and the team will need to interview the entire chain of people involved in this trade.
Finding the origin of a virus is one of the most difficult – and enticing – aspects of infectious disease research. This study has led the scientific community to look for clues in bat caves, illegal animal trade markets, and farms. Yet, finding the origin of any pathogen remains an impossible task and SARS-CoV-2 might be no different.
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