The risk of people with Covid-19 being reinfected is substantially reduced for up to 10 months, researchers have found.
A study of more than 2,000 care-home residents and staff was carried out to test reinfection rates after the first wave of the pandemic in England.
The Vivaldi study, led by University College London, compared those who had an infection up to 10 months earlier, as determined by antibody testing, with those who had not been infected.
“It’s really good news that natural infection protects against reinfection in this time period,” said lead author Dr Maria Krutikov, from the university's Institute of Health Informatics.
"The risk of being infected twice appears to be very low."
The study, published in Lancet Healthy Longevity on Thursday, found residents with a previous infection were 85 per cent less likely to be infected than residents who had not been.
It found staff with past infections were 60 per cent less likely than those who were untouched by coronavirus.
“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,” Dr Krutikov said.
“These findings are particularly important as this vulnerable group has not been the focus of much research.”
For the study, 682 residents and 1,429 staff in 100 care homes in England had antibody blood tests in June and July 2020.
About a third tested positive for antibodies, suggesting they had earlier been infected.
“This was a unique opportunity to look at the protective effect of natural infection in this cohort,” said senior author Dr Laura Shallcross, also from the university.
“An important next step is to investigate the duration of immunity following natural infection and vaccination and to assess whether this protective effect is maintained against current and emerging variants.”
But the researchers said the different rates between staff and residents may not be directly comparable, as staff might have been tested outside the care home, leading to positive tests not included in the study.
And residents who tested positive for antibodies probably represented a particularly robust group, having survived the first wave of the pandemic.
The research was part of the Vivaldi study looking at Covid-19 infections in care homes.
It was funded by the Department of Health and Social Care and involved researchers at the University of Birmingham, Public Health England, Palantir Technologies UK and Four Seasons Healthcare Group.