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.