COVID-19 reinfection not common but elderly more at risk, finds new Lancet study

Vaccination is a better protection from reinfection than past infection, the study noted

By DTE Staff
Published: Wednesday 17 March 2021

Only a few of those who suffered the novel coronavirus disease (COVID-19) tested positive a second time in six months, claimed a new Lancet study. Most such patients were of at least 65 years.

The researchers assessed reinfection rates in Denmark during its first and second wave in 2020 and found that only a 0.65 per cent of the people who were infected in the past tested positive again.

The report found:

Among people who had COVID-19 during the first wave between March and May 2020, only 72 of 11,068 tested positive again during the second wave from September to December 2020. At 3.3 per cent (16,819 of 514,271), the rate of infection was five times higher among people who returned a positive test during the second wave having previously tested negative. 

An analysis of reinfection rate throughout the duration of the epidemic, and not just the second wave, also showed similar results. The study was conducted by researchers from the Staten Serum Institut and University of Copenhagen, Denmark and the European Centre for Disease Prevention and Control, Sweden.

Denmark tested over two-thirds of its population, or around four million people. The researchers calculated the reinfection rates based on the results of these tests.

While only 47 per cent of those over 65 were protected from a repeat infection, around 80 per cent of younger patients did not test negative the second time. The study underlines the importance of adoptation of social distancing norms and other COVID-19 protocals among the elderly, even if they have contracted the virus in the past. It also called for extensive vaccination across age groups. 

The report did not find that protection from reinfection declined after six months. The study focused only on the original strain of the virus and did not take into account the variants. It also did not analyse if more severe symptoms of the disease had any impact on protection from reinfection. 

The paper highlighted antibodies formed during the first infection was not a guaranteed protection and that people who had COVID-19 will still need to vaccinated. The study is significant for countries like India which are threatened by a second wave while mass vaccination is underway.

Infections of other coronaviruses like SARS and MERS whose physical manifestations are similar to COVID-19 assure protection from reinfection for at least three years, the paper said. “Ongoing analysis of COVID-19 is needed to understand its long-term effects on patients’ chances of becoming infected again,” said Dr Daniela Michlmayr, from the Staten Serum Institut, Denmark.

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