People who have had COVID-19 have a reduced chance of being reinfected for at least ten months, according to an analysis published today.
The Vivaldi study, led by UCL researchers, examined COVID-19 infection rates between October and February among 2,111 care home residents and staff in England. They compared them with those who had evidence of a previous infection up to ten months earlier, 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 be infected during the four-month period than residents who had never been infected, while staff who had had COVID were 60% less likely to be reinfected than staff who had not had it.
Writing in Lancet Healthy Longevity, the research team said their findings demonstrated strong protection in both groups. However, they said the figures may not be directly comparable because staff may have accessed testing outside the care home, which would have led to positive tests not being included in the study.
Residents who tested positive for antibodies were also likely to represent a particularly robust group, having survived the first wave of the pandemic, the team, who also included researchers from the University of Birmingham, Public Health England, Palantir Technologies UK and Four Seasons Healthcare Group, added.
Lead author Dr Maria Krutikov, from UCL Institute of Health Informatics, 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.
“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.”
In the study, 682 residents with a median age of 86 and 1,429 staff in 100 care homes underwent antibody blood tests in June and July last year. About one third tested positive for antibodies.
The participants’ PCR tests were then analysed, starting about 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, and positive results were only included if they were more than 90 days apart.
They found ten staff and four residents were reinfected between October and February, while among the 1,477 participants who had never been infected, positive PCR tests occurred in 93 residents and 111 staff.
The study removed participants from the analysis 12 days following their first vaccination dose and the researchers are examining vaccine effectiveness in a separate Vivaldi study.
Senior author Dr Laura Shallcross, from UCL Institute of Health Informatics, 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.”
Krutikov M, Palmer T, Tut G et al. Incidence of SARS-CoV-2 infection according to baseline antibody status in staff and residents of 100 Long Term Care Facilities (VIVALDI study). Lancet Healthy Longevity 4 June 2021
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