A previous bout with COVID-19 provided 80 percent protection against reinfection in those younger than age 65, but just 47 percent protection for those 65 and older, according to findings published March 17 in The Lancet.
The results indicate older adults are more vulnerable to reinfection, researchers said.
The study, conducted in Denmark, evaluated the results of people tested for COVID-19 between Feb. 26, 2020, and Dec. 31, 2020. Researchers compared infection rates between people with positive and negative tests during the first surge, from March to May, and the second surge, from Sept. 1 to Dec. 31.
Of 11,068 people who tested positive during the first wave, 0.65 percent tested positive again during the second wave, compared to 3.27 percent of people who tested negative during the first surge. That translated to an 80.5 percent protection rate for those with a prior infection, but just 47.1 percent protection for those age 65 and older.
The study had a number of limitations, including a small number of older people who were infected, The New York Times reported March 17. Additionally, some of the more transmissible variants that have emerged were not widely recognized during the study period and could not be assessed.
However, the study aligns with previous findings regarding reinfection rates and reinforces the need to prioritize the older adult population.
"Because the older age group is more prone to a serious clinical course of illness, this finding highlights the need to implement protective measures of the older population in the form of effective vaccines and enhanced physical distancing and infection control, even in those known to be previously infected," researchers concluded. "Furthermore, our data indicate that vaccination of previously infected individuals should be done because natural protection cannot be relied on."
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