We are 23 of the 27 original members of the Scientific Advisory Group for the Origins of Novel Pathogens (SAGO) for the World Health Organization (WHO). After approximately 3.5 years of discussions, we completed our independent evaluation of the SARS-CoV-2 virus’s origins, submitting our findings to the WHO director-general in June 2025.
In our 78-page report, we found that most reliable scientific evidence aligns with the idea that SARS-CoV-2 has a zoonotic origin, suggesting it came from an animal. However, we emphasized that until we receive further data, we can’t be entirely sure about the specifics of when, where, and how it entered the human population.
Although the initial term for SAGO concluded in October last year, the WHO has proposed another term for SAGO and is seeking new members. Our 2025 report puts forth suggestions for future investigations into the COVID-19 origins. As the debate around the pandemic’s origins grows increasingly politicized, we, the 23 remaining members, wanted to close the first chapter of SAGO by clarifying our stance on SARS-CoV-2’s origins and the supporting science in a more understandable format.
Among the four original SAGO members who aren’t co-authors of this article, one resigned before our 2025 report was finalized. Three others disagreed with our choice to explore the lab-leak theory because we found no evidence supporting it. We appreciate their contributions and acknowledge one member’s dissent regarding the lab-leak evaluation.
We want to make clear that the viewpoints in this article are ours alone and don’t necessarily reflect the opinions or policies of the WHO or any associated institutions.
The SAGO was established by WHO’s director-general, Tedros Adhanom Ghebreyesus, in November 2021, with a dual mandate: to develop a guiding framework for ongoing inquiries into the origins of SARS-CoV-2, and to explore how emerging pathogens arise in international contexts.
The independent experts from 27 countries involved in SAGO investigated all plausible avenues—not to place blame on any nation but to understand what happened so we can better prevent future epidemics and pandemics.
To examine how SARS-CoV-2 emerged in humans, we evaluated reports of early cases and conducted clinical studies. We looked into potential sources of infection like animal reservoirs, intermediate hosts, and environmental factors. We also analyzed the virus’s genomics and evolutionary biology, including the possibility of a lab escape. Our key findings are detailed in the global framework document published in 2024.
Our conclusions relied on the scientific evidence available. We took into account the work of international teams that visited Wuhan, China—where early cases were identified—in 2020 and 2021. We reviewed relevant scientific publications, preprints, and discussions with experts between November 2021 and June 2025. Additionally, we consulted reviews from various scientific bodies, including the 2022 Lancet Commission, and analyzed publicly accessible intelligence reports.
Four potential scenarios concerning the virus’s origins were proposed before November 2021 through the Joint WHO–China Study, aimed at quickly informing global next steps in response to the outbreak. Here’s an overview of our findings related to each hypothesis:
Hypothesis one: Animals infected with SARS-CoV-2 transmitted the virus to humans.
Most scientific evidence supports this idea. While closely related strains found in bats (e.g., RaTG13 from 2013 and BANAL-52 from 2020) are not direct ancestors of SARS-CoV-2, they indicate that a similar strain might have made the leap to humans or intermediate hosts. The Huanan Seafood Market played a significant role early in the virus’s spread, with over 60% of early cases linked to individuals associated with the market.
Hypothesis two: SARS-CoV-2 was introduced to China’s animal markets through imported goods.
Both the 2021 WHO–China Joint Study and our follow-up report concluded that more data would be needed to support this hypothesis. Despite the Chinese government endorsing this idea, we found that the available evidence doesn’t substantiate it.
Hypothesis three: The virus originated from an accidental laboratory incident.
Key information to evaluate this theory has not been shared with SAGO. Despite repeated requests made to the Chinese government for access to health records of lab workers and safety audits, the information has largely been withheld. Most scientific reviews we consulted support the zoonotic hypothesis and indicate no conclusive evidence for a lab leak. Existing reports appear influenced by political rather than scientific factors.
Hypothesis four: SARS-CoV-2 was created through deliberate manipulation in a laboratory setting.
Our analysis shows no substantial evidence to support this theory when compared to naturally occurring mutations. Research on bat coronaviruses indicates that its genetic structure likely arose from evolution rather than manipulation.
Throughout our work, we encountered various theories, including one regarding a grant proposal called DEFUSE, which sought to create a vaccine based on coronaviruses. We found that claims of developed viruses escaping from U.S. labs are not scientifically supported.
As we conclude our findings, we reiterate the importance of professionals with knowledge regarding SARS-CoV-2’s origins to share that information with the WHO and future SAGO iterations. There’s still much work to do—researching the upstream sources of animals sold at the Huanan Seafood Market and ensuring better biosafety measures are crucial moving forward.
Ultimately, rigorous scientific inquiry, free from conjecture, will be essential for answering the pressing questions about COVID-19’s origins—an event that has profoundly impacted millions of lives and economies worldwide. If we truly seek answers, we must prioritize the sharing of necessary data and promote thorough research efforts.
