Research suggests that a first infection with SARS- CoV-2 provides only 47% protection against a second infection for those aged 65 years and over, compared with 80% protection across all age groups.
These findings underscore the importance of physical distancing and vaccinations, even among those who have already had Covid-19.
The study found that the level of protection against reinfection remained stable for more than 6 months.
However, it did not take into account new variants of the virus, infection with which may provide less immunity against reinfection.
A key factor that will determine how soon life can return to normal after the pandemic is how easily people can reacquire SARS-CoV-2, which is the virus that causes Covid-19.
Proven cases of reinfection have been extremely rare, but the most comprehensive population-based study to date suggests that the risks may be greater than scientists initially thought.
The study, which drew from a register of millions of polymerase chain reaction (PCR) tests carried out in Denmark during 2020, found that an initial infection provided around 80% protection across all age groups.
However, among individuals aged 65 years and older, protection against reinfection dropped to 47%.
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“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,” says senior study author Prof. Steen Ethelberg, Ph.D., of the Statens Serum Institut in Copenhagen, Denmark.
“Given what is at stake,” he adds, “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.”
Scientists know that the immune systems of older adults respond less strongly to infections and vaccinations.
This is known as immunosenescence. Early in the pandemic, Denmark offered free and relatively fast PCR testing for anyone who wanted it, regardless of their symptoms.