Lancet study reveals prior COVID-19 infection reduces contraction risk for 10 months

The risk of being infected with COVID-19 is substantially reduced for up to 10 months following the first infection with the virus, a study published in the Lancet journal said on Tuesday. The research involved checking the rates of COVID-19 infections between October last year and February this year among over 2,000 care home residents and staff in England.

The researchers from University College London (UCL) in the UK compared people who had evidence of a previous infection up to 10 months earlier, with those who had not been previously infected with the virus. They found that previously infected residents were 85% less likely to be infected during this four-month period than those who had never been infected.

Staff members with past infection were 60% less likely to be infected than those who were never infected before. The researchers the results showed strong protection in both groups but cautioned that the two percentages may not be directly comparable. This is because the staff may have accessed testing outside the care home, thus all positive tests not being included in the study, they said.

"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," said study lead author Maria Krutikov, from UCL Institute of Health Informatics.

"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," Krutikov said.

A total of 682 residents, with a median age of 86, and 1,429 staff in 100 care homes underwent antibody blood tests for the study in June and July 2020 following the first wave of Coronavirus. About one-third of residents tested positive for antibodies, suggesting they had previously been infected.

Small reinfection rate

Researchers then analysed the results of their RTPCR tests, approximately 90 days after the blood samples were taken to ensure the tests did not pick up the initial infection. PCR tests were taken once a week for staff, and once a month for residents, with further testing in the event of an outbreak.

Positive test results were only included only after 90 days apart to ensure that the same infection was not recorded more than once. The number of staff and residents who were reinfected between October and February was very small. Based on the antibody test results, out of the 634 people who had been previously infected, reinfections occurred in only four residents and 10 members of staff.

Among the 1,477 participants who had never been infected, positive PCR tests occurred in 93 residents and 111 staff. "This was a unique opportunity to look at the protective effect of natural infection in this cohort ahead of the roll-out of vaccination," said senior study author Laura Shallcross, from UCL Institute of Health Informatics.

(With inputs from agency)