The news: A man in the US caught covid-19 for a second time in the space of just two months, according to a study published in The Lancet Infectious Diseases. That makes him the fifth person to have officially caught the coronavirus twice, after cases recorded in Hong Kong, Belgium, Ecuador, and the Netherlands (although there will certainly be more cases we don’t know about.) However, what’s strange about his case is that he had had a worse bout of illness the second time round. His doctors compared the genome of the virus during each illness and found they were too different to have been caused by the same infection. There’s only one other recorded instance where this has happened—the case in Ecuador.

The details: The 25-year-old man tested positive for the first time on April 18, after experiencing several weeks of symptoms including sore throat, cough, headache, nausea and diarrhoea. He felt fully recovered by April 27, and tested negative for the virus on both May 9 and 26. However just two days later on May 28, he developed symptoms again, this time with fever and dizziness on top of his previous symptoms. He tested positive on June 5 and needed to be treated in hospital after his lungs were unable to get enough oxygen into his body, causing hypoxia and shortness of breath. He had no underlying health conditions. The man has now recovered.

The significance: Being infected once does not mean you’re protected from being infected again, even if such cases are still vanishingly rare, with just five identified out of nearly 40 million confirmed cases worldwide. That means people who have had covid-19 once already still need to stay vigilant, following the advice on social distancing, wearing face masks, and avoiding crowded, poorly ventilated spaces. This was not altogether unexpected, given coronavirus experts warned us that other coronaviruses are seasonal, for example the common cold. However, there are still many questions that researchers are racing to answer—how much protection does having covid-19 confer? Is that mainly through antibodies, or T-cells? How long does protection last? What does it mean for the medical treatments that are being developed, or vaccines? Will we all require a yearly shot rather than a one-off vaccine, for example? If nothing else, this new case is a reminder of how much about this virus we still don’t know.


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