Science, not speculation, is essential to determine how SARS-CoV-2 reached humans.

On Feb 19, 2020, we, a group of physicians, veterinarians, epidemiologists, virologists, biologists, ecologists, and public health experts from around the world, joined together to express solidarity with our professional colleagues in China. Unsubstantiated allegations were being raised about the source of the COVID-19 outbreak and the integrity of our peers who were diligently working to learn more about the newly recognised virus, SARS-CoV-2, while struggling to care for the many patients admitted to hospital with severe illness in Wuhan and elsewhere in China.

It was the beginning of a global tragedy, the COVID-19 pandemic. According to WHO, as of July 2, 2021, the pandemic has resulted in 182 101 209 confirmed cases and 3 950 876 deaths, both undoubtedly underestimates of the real toll. The impact of the pandemic virtually everywhere in the world has been far worse than even these numbers suggest, with unprecedented additional social, cultural, political, and economic consequences that have exposed numerous flaws in our epidemic and pandemic preparedness and in local and global political and economic systems. We have observed escalations of conflicts that pit many parties against one another, including central government versus local government, young versus old, rich versus poor, people of colour versus white people, and health priorities versus the economy. The crisis has highlighted the urgent need to build a better understanding of how science proceeds and the complex, but critical, links science has with health, public health, and politics.

Recently, many of us have individually received inquiries asking whether we still support what we said in early 2020. The answer is clear: we reaffirm our expression of solidarity with those in China who confronted the outbreak then, and the many health professionals around the world who have since worked to exhaustion, and at personal risk, in the relentless and continuing battle against this virus. Our respect and gratitude have only grown with time.

The second intent of our original Correspondence was to express our working view that SARS-CoV-2 most likely originated in nature and not in a laboratory, on the basis of early genetic analysis of the new virus and well established evidence from previous emerging infectious diseases, including the coronaviruses that cause the common cold as well as the original SARS-CoV and MERS-CoV. Opinions, however, are neither data nor conclusions. Evidence obtained using the scientific method must inform our understanding and be the basis for interpretation of the available information. The process is not error-free, but it is self-correcting as good scientists endeavour to continually ask new questions, apply new methodologies as they are developed, and revise their conclusions through an open and transparent sharing of data and ongoing dialogue.

The critical question we must address now is, how did SARS-CoV-2 reach the human population? This is important because it is such insights that will drive what the world must urgently do to prevent another tragedy like COVID-19. We believe the strongest clue from new, credible, and peer-reviewed evidence in the scientific literature3, 4, 5, 6 is that the virus evolved in nature, while suggestions of a laboratory-leak source of the pandemic remain without scientifically validated evidence that directly supports it in peer-reviewed scientific journals.7, 8

Careful and transparent collection of scientific information is essential to understand how the virus has spread and to develop strategies to mitigate the ongoing impact of COVID-19, whether it occurred wholly within nature or might somehow have reached the community via an alternative route, and prevent future pandemics. Allegations and conjecture are of no help, as they do not facilitate access to information and objective assessment of the pathway from a bat virus to a human pathogen that might help to prevent a future pandemic. Recrimination has not, and will not, encourage international cooperation and collaboration. New viruses can emerge anywhere, so maintaining transparency and cooperation between scientists everywhere provides an essential early warning system. Cutting professional links and reducing data sharing will not make us safer.

We welcome calls for scientifically rigorous investigations.10, 11 To accomplish this, we encourage WHO and scientific partners across the world to expeditiously move to continue and further extend their initial investigation with experts in China and the Chinese Government. WHO's report from March, 2021, must be considered the beginning rather than the end of an inquiry, and we strongly support the G7 leaders' call for “a timely, transparent, expert-led, and science-based WHO-convened phase 2 COVID-19 origins study”. We also understand that it might take years of field and laboratory study to assemble and link the data essential to reach rational and objective conclusions, but that is what the global scientific community must strive to do.

It is time to turn down the heat of the rhetoric and turn up the light of scientific inquiry if we are to be better prepared to stem the next pandemic, whenever it comes and wherever it begins. Meanwhile, people around the world continue to be infected by SARS-CoV-2, many are suffering severe disease and long-term sequelae, and too many are dying. Too many populations lack access to SARS-CoV-2 testing, COVID-19 treatments, and safe and effective vaccines, which will inevitably perpetuate the pandemic and its consequences. At the very least, we owe it to all who have suffered from COVID-19, as well as our families and the global community, to work collaboratively to end the pandemic and support international efforts to ensure vaccine equity, even as we prepare for the next pandemic.

Having robust surveillance and detection systems in place across the globe is essential to detect and report new or evolving pathogens that can potentially unleash the next local or global threat, as required by the International Health Regulations. Equally essential will be ensuring that the field workforce, laboratory facilities, and the health-care community can all work under the safest conditions. Until this pandemic ends, we ask, as we did in February, 2020, for solidarity and rigorous scientific data.