Most of the world‘s population has been infected at least once by Sars-Cov-2. In the US, some estimates suggest that 65% of people have had multiple infections, and we are all set to contract Covid-19 multiple times in the decades to come. How much damage repeated infections will cause, though, is a matter of debate among researchers, reports an article in Nature Online.
“There’s a polarization on the subject,” says Danny Altmann, an immunologist at Imperial College London. Some scholars argue that Sars-CoV-2 is a common respiratory virus, especially for those who have been vaccinated. Others believe that every contagion carries a risk of long-term harm and repercussions. The good news is that when re-infection occurs, the immune system seems poised to respond: a study of US National Basketball Association players found that re-infected players cleared the virus in an average of 5 days, compared to 7 for a first infection.
Other studies have shown that people who experience mild symptoms with their first infection are likely to have a mild infection later. A study in Qatar of 7,300 people found that the chances of severe illness upon reinfection were almost 90% lower than those from a primary infection. This is confirmed by a study that looked at 3.8 million first infections and 14,000 reinfections in England, finding that people were 61% less likely to die in the month following reinfection than after a first infection.
However, reinfection is not without risk. Those who are more vulnerable during a first infection continue to be so in subsequent ones. A study by the National Covid Cohort Collaborative in the United States of more than 16 million people found that a second serious infection was much more common in those who had a first serious infection.
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