Five years ago, the covid-19 pandemic was getting under way – but we didn’t know it yet. So, what exactly happened? Many scientists are convinced that it began with infected animals at a market in Wuhan, China, late in 2019, but there is still some debate.
It is clear that SARS-CoV-2 evolved from a bat virus, as many related viruses have been found in bats. One of the closest is a strain called , isolated from a Malayan horseshoe bat (Rhinolophus malayanus).
What we don’t know is exactly how the virus got from bats to people. The first covid-19 cases in people confirmed by genetic sequencing occurred in Wuhan in December 2019.
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Some studies have claimed that SARS-CoV-2 infected people prior to this month, but these rely on indirect methods, such as looking for antibodies in stored blood, so they are not conclusive, says at Temple University in Pennsylvania.
The first confirmed cases were clustered around a market in Wuhan where live animals were kept. Samples taken in January 2020 by swabbing surfaces at the market showed that the virus was present.
Most of the positive samples were from the part of the market where mammals were kept. These also confirm the presence of animals such as raccoon dogs, which can be infected by covid-19. What’s more, there were two covid-19 variants from the start, differing by two mutations. Both were found at the market.
This suggests that a bat virus jumped to animals such as raccoon dogs, possibly decades ago, and that infected animals eventually ended up at the market, where they passed the virus on to people. But not all researchers are convinced. “The big issue is that we don’t have evidence of any infected animals,” says Pond.
Another possibility is that the virus somehow came from the Wuhan Institute of Virology or the Wuhan Center for Disease Control and Prevention – the “lab leak” hypothesis.
“Of all the cities in China that have these live animal markets, the one that covid emerged in was the one with two labs working on coronaviruses. It is an extraordinary coincidence,” says at the University of Edinburgh, UK. “But I’m not saying it’s not a coincidence.”
Indeed, there is no evidence that SARS-CoV-2 or any precursor to it was ever present at either establishment. Nonetheless, Woolhouse regards the case as open. “I don’t know how covid-19 started, and I don’t see how other scientists can know either.”
Others think there is enough evidence pointing at animals in the market to say the case is solved. “There are a lot of things that can’t 100 per cent be ruled out,” says at the University of Oxford. “Like we can’t 100 per cent rule out that it was brought to earth by aliens – but it wasn’t.”
What happened after covid-19 began spreading in people is clearer. On 28 December 2019, a virologist in Beijing submitted a to an international database, but no one realised what it was and because of technical issues with the submission, it was deleted.
Three days later, the World Health Organization (WHO) was told of a in Wuhan of unknown cause.
It soon became clear that a new coronavirus was causing the cases, and on 12 January, another sequence was made publicly available. This time, researchers knew what it was – and within two days, a team at Moderna had designed the first mRNA vaccine against it.
By this time, the virus had already spread beyond China, with a case in Thailand reported on 13 January. Ten days later, China locked down Wuhan. At this stage, the infection fatality rate remained unclear, and rumours about how deadly it was abounded.
Around the same time, a WHO committee decided not to declare a public health emergency of international concern. But by 30 January, with reports of the new coronavirus spreading outside China, the WHO did declare a public health emergency.
On 11 February, the WHO officially named the disease caused by the SARS-CoV-2 virus as “covid-19″. During February, it spread to dozens of countries around the world, and it became clear that a pandemic was under way.
For several weeks, however, the WHO conspicuously avoided using the term “pandemic”. But on 11 March, when there were already more than 100,000 confirmed cases in over 100 countries and at least 4000 deaths, the WHO finally called the situation what it was.
The rest, as they say, is history.
