Reinfection with Covid-19 rare, but more common in people 65 and over: large Danish study in Lancet

Most people who have had Covid-19 are protected from catching it again for at least six months, but elderly patients are more prone to reinfection, according to a study published in The Lancet.

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SARS-CoV-2, the cause of the Covid-19 epidemic, has resulted in more than 117 million cases and more than 2.6 million deaths worldwide as of March 7, 2021, according to the Organization’s estimates world health. However, the degree to which infection with SARS-CoV-2 confers protection against subsequent reinfection is not well described.

In 2020, as part of Denmark’s broad free PCR testing strategy, around 4 million individuals (69% of the population) were tested. Using this national PCR test data from 2020, the researchers estimated the protection against repeated infection with SARS-CoV-2.

A large-scale assessment of reinfection rates in Denmark in 2020 confirms that only a small proportion of people (0.65%) returned a positive PCR test twice.

However, while a previous infection gave those under 65 about 80% protection against re-infection, for those aged 65 and over it only offered 47% protection, indicating that they are more likely to catch Covid-19 again.

The authors of the first such large-scale study found no evidence that protection against reinfection worsened over a six-month follow-up period.

Their findings underscore the importance of measures to protect older people during the pandemic, such as better social distancing and prioritization of vaccines, even for those who have recovered from Covid-19. The analysis also suggests that people who have had the virus should still be vaccinated, as natural protection – especially in the elderly – cannot be relied on.

As of January 2021, Covid-19 had resulted in more than 100 million cases and more than 2 million deaths worldwide. Recent studies have suggested that re-infections are rare and that immunity can last for at least six months, but the degree to which capture of Covid-19 confers protection against repeated infection remains poorly understood.

Dr Steen Ethelberg, Statens Serum Institut, Denmark, said: ‘Our study confirms what a number of others seem to suggest: re-infection with Covid-19 is rare in younger, healthy people, but older people are more at risk of catching it. again. Since older people are also more likely to have severe symptoms of the disease and unfortunately die, our results clearly show how important it is to implement policies to protect older people during the pandemic. Given what is at stake, the results underscore how important it is for people to adhere to measures implemented to protect themselves and others, even if they have already had Covid-19. Our knowledge could also inform policies focused on broader vaccination strategies and the relaxation of lockdown restrictions. “