Previous COVID-19 infection reduces the risk of infection by up to 10 months

According to new findings from the Vivaldi study led by UCL researchers, the risk of being infected with SARS-CoV-2, the virus that causes COVID-19, is substantially reduced up to 10 months after the first infection.

For the study, published in Lancet Healthy Longevity, researchers examined rates of COVID-19 infections between October and February among more than 2,000 nursing home residents and staff, comparing those who had evidence of a previous infection up to 10 months earlier, as determined by antibody testing, with those who had not been previously infected.

They found that residents with a previous infection were 85% less likely to become infected during this four-month period than residents who had never been infected, while staff with a past infection were 60% less likely to become infected. odds that staff who had not had the infection before.

The researchers said this showed strong protection in both groups, but warned that the two percentages may not be directly comparable, as staff may have accessed the tests outside the care home, which makes it impossible. positive tests are included in the study. Also residents who tested positive antibodies it probably represented a particularly robust group, which had survived the first wave of the pandemic.

The main author, Dra. Maria Krutikov (UCL Institute of Health Informatics) said: “It is good news that natural infection protects against reinfection in this period of time. The risk of getting infected twice seems to be very high. low.

“The fact that previous COVID-19 infection gives a high level of protection to residents at home it is also reassuring, given past concerns that these people might have less robust immune responses associated with increasing age. These findings are particularly important, as this vulnerable group has not been the focus of much research. “

For the study, 682 residents (with an average age of 86 years) and 1,429 employees from 100 care homes in England underwent antibody blood tests in June and July last year after of the first wave of COVID-19. About a third tested positive for antibodies, suggesting that they had previously been infected.

The researchers analyzed the results of the participants’ PCR tests, beginning approximately 90 days after the blood samples were taken to ensure that tests did not detect the initial infection. PCR tests were performed once a week for staff and once a month for residents, with subsequent tests in case of an outbreak. Positive test results were only included if more than 90 days were separated to ensure that the same infection was not included more than once.

The number of staff and residents who were reinfected between October and February was greatly reduced. According to the results of antibody tests, of the 634 people who had been previously infected, reinfections occurred in only four residents and 10 staff members. Among the 1,477 participants who had never been infected, positive PCR tests were performed on 93 residents and 111 employees.

The study excluded the impact of vaccination by removing participants from the analysis 12 days after their first dose of vaccination. The authors address the issue of vaccine efficacy in a separate study by VivaIdi.

Lead author Dr. Laura Shallcross (UCL Institute of Health Informatics) said: “This was a unique opportunity to look at the protective effect of natural infection in this cohort before vaccination was launched.

“An important next step is to investigate the duration of immunity after nature infection and vaccination and assess whether this protective effect against current and emerging variants is maintained.

“We want to thank everyone staff and residents who volunteered their time and voluntarily donated their blood for antibody testing, as well as Four Seasons Healthcare, whose collaboration with researchers made it possible. ”