Surviving COVID-19 is not a guarantee you won’t get it again, scientists say, and the chance of reinfection is much higher if you’re age 65 and older.
In a population level observational study, researchers in Denmark collected data from the Danish Microbiology Database and analyzed infection rates during during the country’s second surge of the COVID-19 epidemic, which was September 1 through December 31.
The scientists then compared those findings to infection rates during the first surge, which was March-May 2020.
The study found that of the 11, 068 people who tested positive for COVID-19 during the first surge, only 72 were positive during the second surge.
Overall, protection against reinfection was 80.5%. There was little difference between male and female protection rates (78.4% of males and 79.1% of females).
The study also found protection against reinfection was 79.3% three to six months after recovery, and 77.7% at more than seven months.
One group benefited much less, however, the researchers found. Those ages 65 and older enjoyed only a 47.1% rate of protection.
“Our finding that older people were more likely than younger people to test positive again if they had already tested positive could be explained by natural age-related changes in the immune system of older adults, also referred to as immune senescence,” the scientists wrote. “Our analysis highlights the need to protect older people against reinfection with SARS-CoV-2 by vaccination, physical distancing measures, and personal protective equipment, such as facemasks, regardless of previous infection status.”
“Furthermore,” the group wrote, “our data indicate that vaccination of previously infected individuals should be done because natural protection cannot be relied on.”
The study was published last week in the medical journal Lancet.
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