Can you get sick of Covid-19 again? Should the recovered get the vaccine? How long does immunity last? These are crucial issues and a maxi study offers some answers. It is the first on a large scale and was conducted in Denmark, assessing the country’s 2020 reinfection rates. The results, published in ‘The Lancet’, confirm that reinfections with the Sars-CoV-2 coronavirus are rare, but – the authors add – more common among the elderly. In fact, it emerges that those over 65 are more at risk of getting infected again. In this age group, protection from repeated infections is 47%, compared to 80% recorded among the youngest, the under 65s.
However, a previous infection has a shield effect on the majority of people healed: according to the data collected by the Danish study, only 0.65% of patients had a positive test twice, during the first and second waves faced by the country, compared to 3.27% of people who tested positive for the first time (who therefore had a 5 times higher infection rate). Another fact that emerges from the research is that immunity remains stable for more than 6 months.
“There is no evidence that protection falls within 6 months of infection”, highlights Daniela Michlmayr, of the Danish Staten Serum Institut, also recalling that “it has been shown that the closely related SARS and MERS coronaviruses confer protection immune system against reinfections that lasts up to 3 years “. Covid now needs a continuous long-term analysis, he adds. The authors point out an important aspect of this analysis: it is a work that focused on the original strain of Sars-CoV-2 and did not evaluate the variants.
The greater risk of getting sick in the elderly highlights the importance of measures to protect them during the pandemic, with greater distancing and “priority over vaccines, even for those who are cured”. The analysis suggests that, in general, people who have had the virus should still be vaccinated, and that “natural protection cannot be relied upon” exclusively.
The Danish scientists drew on the data collected as part of the national free swab screening initiative that allowed to test more than two thirds of the population (4 million people, 69%) in 2020. Given the time span to to which reference was made, it was not possible to estimate the protection against reinfection by Sars-CoV-2 variants and the authors stress that further studies on this are necessary. A focus was also dedicated to healthcare workers, who have greater exposure to the virus. Also in this sub-analysis the results obtained were similar: 1.2% of those who had had Covid in the first wave were reinfected, compared to the infection rate of those who had never met the virus of 6.2%. Estimated protection of 81.1%.
“Compared to more formal analyzes of reinfection cases that rely on viral sequence data, many will find this natural immunity data relatively alarming: only 80% protection from reinfection, which drops to 47% in people over 65. years, that’s a more troubling rate than previous studies offer, “Imperial College London experts Rosemary J. Boyton and Daniel M. Altmann note in a related comment. The Danish results, they conclude, “are confirmation, if necessary, that for Sars-CoV-2 the hope of protective immunity through natural infections may not be within our reach and a comprehensive vaccination program with highly effective vaccines. instead it is the lasting solution “.