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Fewer than 1% of people who previously tested positive for COVID-19 are reinfected with the virus

The majority of people who test positive for COVID-19 are protected from being reinfected with the virus for at least six months, a new study suggests.

Researchers found that fewer than one percent of people in Denmark in 2020 caught coronavirus twice.

In addition, those who were aged 65 or older were 46 percent more likely than younger or middle-aged adults to be reinfected.

The team, led by the Statens Serum Institut in Copenhagen, says the findings provide further evidence that coronavirus mitigation measures are essential to maintain until enough people are vaccinated to achieve herd immunity.

A new study found that just 0.65% who tested positive during the first wave were reinfected during the second wage compared to 3.3% who were newly infected (above)

mong senior citizens, 0.88% of senior citizens were reinfected during the second wave, making them up 46% more likely to test positive twice than younger adults. Pictured: The number of tests done per person

 mong senior citizens, 0.88% of senior citizens were reinfected during the second wave, making them up 46% more likely to test positive twice than younger adults. Pictured: The number of tests done per person

‘Our study confirms what a number of others appeared to suggest: reinfection with COVID-19 is rare in younger, healthy people, but the elderly are at greater risk of catching it again,’ said Dr Steen Ethelberg, from the Statens Serum Institut.

Cases of presumed reinfection have cropped up in other parts of the world, but questions have arisen about testing accuracy.

Last year, University of Hong Kong researchers reported details of a 33-year-old man who had recovered in April from a severe case of COVID-19 and was diagnosed four months later with a different strain of the virus.

Additionally, two European patients, one in Belgium and one in the Netherlands, were reported to have been reinfected with the virus.

And in Nevada, a 25-year-old man become the first person in the U.S. to be struck down with the coronavirus for a second time – which hit him harder than his first bout of the disease. 

For the new study, published in The Lancet, the team analyzed data that was collected during Denmark’s national testing strategy in 2020 during the country’s first and second waves.

During the first wave between March and May 2020, 11,068 Danes tested positive for COVID-19 and 514,271 tested negative.

Comparatively, during the second wave from September to December 2020, 72 of the people who tested positive in the first wave, just 0.65 percent, were reinfected.

Additionally, 16,819 of the people who tested negative, 3.3 percent, tested positive during the second surge.

Results showed the rate of infection was five times higher among reinfected people than people who previously tested negative. 

Of people under age 65 who were infected with COVID-19 during the first wave, 0.6 percent tested positive once mored during the second wave 

However, 0.88 percent of senior citizens who tested positive during the first wave were reinfected during the second wave, making them up 46 percent more likely to test positive twice.

‘Since older people are also more likely to experience severe disease symptoms, and sadly die, our findings make clear how important it is to implement policies to protect the elderly during the pandemic,’ said Ethelberg.

‘Given what is at stake, the results emphasize how important it is that people adhere to measures implemented to keep themselves and others safe, even if they have already had COVID-19. Our insights could also inform policies focused on wider vaccination strategies and the easing of lockdown restrictions.’

In a linked editorial, Professors Rosemary J Boyton and Daniel M Altmann, from Imperial College London, said that the findings show the importance of vaccinating.

‘Set against the more formal reinfection case reports that are based on differential virus sequence data and make reinfection appear an extremely rare event, many will find the data reported by Hansen colleagues about protection through natural infection relatively alarming,’ they wrote. 

‘These data are all confirmation, if it were needed, that for SARS-CoV-2 the hope of protective immunity through natural infections might not be within our reach and a global vaccination program with high efficacy vaccines is the enduring solution.’ 


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