The risk for reinfection with SARS-CoV-2 is generally low, but it is higher among adults aged 65 and older, according to a population-based study from Denmark published in The Lancet.

Researchers examined polymerase chain reaction (PCR) test results among roughly 525,000 people who were tested for SARS-CoV-2 from February through December 2020. Of some 11,000 who tested positive during the first surge of the pandemic in March-May, just 0.7% tested positive again during the second surge in September-December. Of those who tested negative during the first surge, 3.3% tested positive during the second surge.

In a separate analysis, the reinfection rate was 8 per 100,000 person-days of follow-up among people aged 65 and older, versus 4-6 per 100,000 person-days among younger age groups.

Researchers say, "The quality, quantity, and durability of protective immunity elicited by natural infection with SARS-CoV-2 are poor relative to the much higher levels of virus-neutralising antibodies and T cells induced by the vaccines." They add, "The hope of protective immunity through natural infections might not be within our reach, and a global vaccination programme with high efficacy vaccines is the enduring solution."