A single dose of either the Oxford-AstraZeneca or Pfizer vaccine gives residents of care homes substantial protection against SARS-CoV-2 infection after four weeks, according to new pre-print findings from the Vivaldi study led by UCL researchers.
The study, funded by the Department of Health and Social Care and sponsored by UCL via the Joint Research Office, looked at data from more than 10,000 care home residents in England, with an average age of 86, between December and mid-March, comparing the number of infections occurring in vaccinated and unvaccinated groups.
It found that a single vaccine dose was effective at preventing 56% of infections after four weeks, rising to 62% of infections after five weeks. The timing and size of the protective effect was similar for both vaccines.
Dr Maddie Shrotri (UCL Institute of Health Informatics) said: “Our study suggests that both vaccines currently in use in the UK are effective at reducing infections in frail, older adults. This new evidence is important because there is currently limited data about vaccine efficacy for this vulnerable population.”
Researchers also found evidence suggesting the infections occurring post-vaccine may be less infectious.
Dr Laura Shallcross (UCL Institute of Health Informatics) said: “Our findings show that a single dose has a protective effect that persists from four weeks to at least seven weeks after vaccination. Vaccination reduces the total number of people who get infected, and analysis of lab samples suggests that care home residents who are infected after having the vaccine may also be less likely to transmit the virus.
“We can also infer that the vaccines protect against the highly transmissible UK variant, as this was prevalent during the study period*.”
Chief Medical Officer for England, Professor Chris Whitty said: “These data add to the growing evidence that vaccines are reducing Covid-19 infections and doing so in vulnerable and older populations, where it is most important that we provide as much protection from Covid as possible.”
The research is part of the ongoing Vivaldi study, launched in June last year, to investigate Covid-19 infections in care homes and inform strategies to protect residents. The study is a collaboration between researchers from UCL and the University of Birmingham and healthcare providers including Four Seasons Healthcare, HC-One, The Orders of St John Care Trust, and Friends Of The Elderly.
Read more about the research.
Image: pavasaris / Adobe Stock