62% protection from single vaccine dose study proves
The study looked at data from more than 10,000 care home residents in England with an average age of 86 between December and mid-March.
A single dose of either the Oxford-AstraZeneca or Pfizer vaccines gives residents of care homes substantial protection according a study in which The Orders of St John Care Trust was a key part.
The study, led by UCL researchers and funded by the Department of Health and Social Care, 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 PCR-confirmed 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. Looking at the Pfizer and Oxford-AstraZeneca vaccines separately, they found that the timing and size of the protective effect was similar for both vaccines.
Dr Maddie Shrotri of the UCL Institute of Health Informatics, said: “Our study suggests that both vaccines currently in use in the UK are effective at reducing PCR-positive infections in frail, older adults. This new evidence is important because there is currently limited data about vaccine efficacy for this vulnerable population.”
Dan Hayes, Chief Executive of The Orders of St John Care Trust, said: “The results of this study are extremely encouraging. OSJCT has been committed to ensuring all of our residents and colleagues have access to the vaccines since they first became available because we recognise they are a vital part of the roadmap towards returning to some form of normality.
“We have been at the forefront of projects such as this and COVID-19 testing pilots because we recognise that as a leading social care provider we have a key role in looking after not just our current residents but also those who choose or require our care in the future.”
Researchers also found evidence suggesting the infections occurring post-vaccine may be less infectious. Analysing lab samples from positive PCR tests, they found that samples taken at least 28 days after the first vaccine dose contained less of the virus, meaning they were “weaker” positives.
Dr Laura Shallcross of the UCL Institute of Health Informatics said: “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.
The study looked at PCR test result data for 10,412 long-term care home residents from 310 care homes. The residents were all over the age of 65, with an average age of 86, and had routine monthly PCR tests as well as further targeted tests if an outbreak was suspected.
The data included a total of 36,352 PCR results, of which 1,335 were positive. Researchers estimated the effectiveness of the vaccine by looking at the number of infections within specific time periods after vaccination (e.g., 0-6 days, 7-13 days, 14-28 days) and comparing these to the number of infections that occurred before vaccination.
Among care home residents who had previously been infected by SARS-CoV-2, a single vaccine dose appeared to have little impact, suggesting people who have a prior infection are already well protected. However, only 11% of people in the study had been infected with SARS-CoV-2 before, so these early findings require further research.
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 such as Four Seasons Healthcare, HC-One, The Orders of St John Care Trust, and Friends Of The Elderly.
Dr Shallcross added: “This timely evidence on the real-world effectiveness of vaccines shows the value of collaboration between care homes and research teams. We would like to thank the healthcare providers who shared their data with us.”