First case of coronavirus reinfection leaves big questions unanswered

By Jessica Hamzelou

Commuters wearing face coverings in Hong Kong

Lam Yik/Bloomberg via Getty Images

A healthy 33-year-old man is the first person confirmed to have caught the coronavirus twice, according to unpublished research from the University of Hong Kong. As details of the case emerge, researchers say there is still much we don’t know.

“There have been anecdotal reports of people being reinfected,” says Charlotte Houldcroft at the University of Cambridge, who wasn’t involved in the work. “But this is the first time that there’s good immunological data on the individual.”

According to a press release and pages of an as-yet unpublished scientific paper that have circulated on social media, the man first became unwell in Hong Kong in March. His symptoms were mild and included a fever, sore throat and cough. A test confirmed that he had covid-19 on 26 March.

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In August, the man travelled from Spain to Hong Kong via the UK. On arrival in Hong Kong on 15 August, he again tested positive for the coronavirus, despite not having any symptoms.

On both occasions, viral samples taken from the man were sequenced to study the virus’s genome. A comparison of the two samples revealed that they appear to be from different lineages – although both are derived from a recent common ancestor, they have several genetic differences.

“We could have expected this, given what we know about the way immunity wanes,” says Stephen Griffin at the University of Leeds, UK. The work comes from a reputable research group, and the genetic differences and time lag between the two virus infections suggest they really were separate, he says. “I’d be surprised if this was an error, but you can’t be absolutely certain until the data has been properly scrutinised.”

Researchers don’t yet know how common reinfection might be – if immunity lasts for months, we would only expect to see reinfection cases some time after the start of the pandemic. It is also unclear whether the man or any people who become reinfected are infectious to others. “If people can be infected again, but they have no symptoms and they don’t infect anyone else, that doesn’t really matter,” says Houldcroft.

The findings reinforce warnings that people who have been infected aren’t necessarily immune to the coronavirus, says Griffin. “Just because you’ve had it once, which is still a relatively small fraction of the population, you could theoretically get it again.”

The two lineages of the virus wouldn’t be considered different strains, says Houldcroft. While the two forms of the virus have genetic differences, it isn’t clear if they vary in the way they behave or how they affect people. “We don’t know whether (the differences) are important for how the body recognises them immunologically or how the body combats them,” she says. More than 100 lineages of the coronavirus have been identified so far, but we don’t yet know if more than one strain exists.

This case suggests that even people who have recovered from a coronavirus infection should be considered for vaccination, if and when a vaccine becomes available, said Kelvin Kai-Wang To at the University of Hong Kong and his colleagues, who conducted the research, in a press release. The team members said that individuals should also continue to follow guidance on limiting the spread of the virus, such as mask-wearing and social distancing.

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