Risk of catching Covid again falls ‘substantially’ for up to 10 months after first infection, UCL research finds

The risk of catching coronavirus is “substantially” reduced for up to 10 months following a first infection, according to a new study.

Prior Covid-19 infection can significantly lower the risk of being infected with SARS-CoV-2, the virus that causes Covid-19, University College London (UCL) researchers behind the Vivaldi study say.

The study looked at Covid-19 infection rates between October and February among more than 2,000 care home residents and staff, comparing those who antibody blood testing had shown to have evidence of a previous infection up to 10 months earlier, with those who had not been previously infected.

Out of the 682 residents (with a median age of 86) and 1,429 staff who took part in the study, about a third tested positive for antibodies in June and July – suggesting they had previously been infected.

Of the 634 people who had been previously infected, the number of staff and residents who were reinjected between October and February was very small.

Among the 1,477 participants who had never been infected, positive PCR tests occurred in 93 residents and 111 staff.

Residents who had previously been infected with SARS-CoV-2 were shown to be 85% less likely to be infected during this four-month period than residents who had never been infected.

Meanwhile staff with past infection were 60% less likely than staff who had not been previously infected.

The findings were “really good news” and showed natural infection protects against reinfection in this time period, according to the study’s lead author, Dr Maria Krutikov from the UCL Institute of Health Informatics.

She said: “The risk of being infected twice appears to be very low. 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.

“These findings are particularly important as this vulnerable group has not been the focus of much research.”

But researchers behind the study warned the two results may not be directly comparable, as staff may have accessed testing outside the care home, leading to positive tests not being included in the study.

They added that residents who participated in the study who had tested positive for antibodies likely represented a particularly robust group, having survived the first wave of the pandemic.

Senior author Dr Laura Shallcross said: “This was a unique opportunity to look at the protective effect of natural infection in this cohort ahead of the roll-out of vaccination.

“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.

“We would like to thank all those staff and residents who volunteered their time and willingly gave their blood for antibody testing as well as Four Seasons Healthcare, whose collaboration with researchers made this possible.”