Covid reinfections 'to be expected' as virus spreads, say government scientists

Government science advisers have warned that reinfections with Covid-19 are “to be expected” as the virus spreads, based on what is known about people’s immunity to other coronaviruses that cause the common cold.

Researchers on the Covid-19 Genomics UK Consortium said it was unclear at what point people who had recovered from the virus became vulnerable to reinfection, but cited emerging reports of second infections that suggested the timeframe was “relatively short”.

There are seven types of coronavirus that infect humans, the deadliest being Sars, Mers and Sars-Cov-2 – the virus that causes Covid-19. The four others, which are in general circulation, cause common colds and can reinfect people six months after they have fought off the same virus.

The paper, released with a batch of Sage documents on Friday, suggests that large-scale genomic surveillance of the virus from positive test swabs could help identify cases of reinfection in the UK, but that such a system would require people to understand that once they have had Covid-19 they can be reinfected, and should get tested again if they develop symptoms.

The document describes how the first person to have a confirmed Sars-Cov-2 reinfection, a 33-year-old man from Hong Kong, may have picked up his second infection when he passed through the UK in August on his way home from Spain. Although the strain that caused the second infection was predominantly circulating in the UK at the time, it may have been exported to Spain at an earlier date, the geneticists write.

In the case of the man from Hong Kong, the first infection caused mild symptoms, while the second was asymptomatic and only spotted when he walked through a testing point at the airport. This suggests that he was better able to fight the virus the second time around, but also raises the prospect that reinfected people could unwittingly spread the virus without knowing they are ill.

The scientists state that if reinfected people can be asymptomatic, it is “imperative” to find out whether they are likely to be infectious. “Clearly, if reinfections are both asymptomatic and infectious, this could pose challenges for any symptoms-based measures,” such as the testing and self-isolation advice used to control the epidemic.

The paper follows the release of the minutes from a Sage meeting on 3 September when the expert committee noted that there had been a small number of well-documented cases of reinfection. While such cases are apparently rare, the advisers warned that reinfected people may shed as much virus as those who are infected for the first time, and so be infectious to others. The possibility meant people would need to follow testing and self-isolation guidelines upon falling ill even if they had had Covid-19 before, they added.

Doctors have reported nearly two dozen cases of suspected or confirmed Covid-19 reinfections, but the real number is thought to be far higher, since most reinfections are not recorded. While most reinfections are milder than the original infection, some cases reported in the US, the Netherlands, Spain and India have described more severe symptoms the second time round.