Prior COVID infection cuts contraction risk by 10 months: Study

University College London (UCL) scientists have found that previous COVID infection substantially reduced the risk of a new infection for up to 10 months afterwards in their study of care home residents and staff.

The study, published in The Lancet Healthy Longevity on Thursday (June 3), found that care home residents who had been previously infected with the virus were about 85 per cent less likely to be infected between October and February than those who had not been infected.

For staff, those with a past infection were around 60 per cent less likely to become infected again.

“It’s really good news that natural infection protects against reinfection in this time period. The risk of being infected twice appears to be very low,” the study’s lead researcher, Maria Krutikov of the UCL Institute of Health Informatics, said.

Also read: After COVID vaccination, only 0.06% chance of hospitalisation, says study

“The fact that prior Covid-19 infection gives a high level of protection to care home residents is also reassuring, given past concerns that these individuals might have less robust immune responses associated with increasing age.”

The study involved 682 care home residents, with a median age of 86, and 1,429 staff in care homes. Tests conducted in June and July last year showed around a third were positive for the presence of COVID antibodies.

The study excluded the impact of vaccination by removing people 12 days following a first vaccine dose. The authors plan to look at vaccine effectiveness in a separate study.

Alexander Edwards, an associate professor in biomedical technology at the University of Reading who was not involved in the study, said there was still much uncertainty about the extent and duration of protection following infection.

“We still expect natural infection should protect against more severe infection, but we still don’t have enough data to know this,” he said.

Also read: Vaccine-induced antibodies less effective against coronavirus variants: Study

The researchers said the study period covered the emergence of the more contagious variant first identified in the UK and now known as Alpha, implying a good level of protection against that variant. However, the concerning variant initially discovered in India and now designated the Delta variant has subsequently emerged and become dominant in Britain.

At the start of the pandemic, researchers lacked an understanding of how natural immunity to SARS-CoV-2 might develop. But that quickly changed. Within months, studies had shown that infected people can make antibodies that neutralize the virus, as well as ‘T’ cells that can recognize and kill SARS-CoV-2-infected cells, according to Nature.