Monday, July 4

Having passed the Covid-19 protects against a new contagion up to ten months later



Have passed the Covid-19 notably reduces the risk of a new contagion until 10 months later of the first infection, according to new findings from the Vivaldi study led by researchers at University College London (UCL).

For the study, published in «
Lancet Healthy Longevity
»The researchers analyzed the rates of Covid-19 infections between October and February of more than 2,000 residents and staff of nursing homes. They compared those who had evidence of prior infection up to 10 months earlier, as determined by antibody testing, with those who had not previously been infected.

They found that residents with a prior infection had a 85% less likely to get infected during the study period than those who had never been infected, while staff with a previous infection were 60% less likely than workers who had not had the disease before.

The researchers said this showed a strong protection in both groups. “It is really good news that natural infection protects against reinfection in this period of time.The risk of getting infected twice appears to be very low. The fact that a previous Covid-19 infection provides a high level of protection to nursing home residents 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, ”says Dr. Maria Krutikov (UCL Institute for Health Informatics), first author of the research.

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

Weekly tests

The researchers then analyzed the results of the participants’ PCR tests, which began approximately 90 days after the blood samples were taken, to make sure the tests did not detect the initial infection. PCR testing was done 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 if they were separated by more than 90 days 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 very small. According to the results of the antibody test, 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 occurred in 93 residents and 111 staff members.

The study excluded the impact of vaccination by removing participants from the analysis 12 days after their first immunization dose.

«This was a unique opportunity to observe the protective effect of natural infection in this cohort before the launch of vaccination. An important next step is to investigate the duration of immunity after natural infection and vaccination and to assess whether this protective effect is sustained against current and emerging variants, ”says lead research author Dr. Laura Shallcross (Institute of UCL Health Informatics).

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