A single dose of Pfizer or AstraZeneca Covid-19 vaccine offers around 60 per cent protection against infection from SARS-CoV-2 in adults aged 65 years and above, according to a study published in The Lancet Infectious Diseases. To obtain real-world data on the effectiveness of these vaccines in care homes, the researchers from the University College London (UCL) in the UK used data from the VIVALDI study.
That research investigated SARS-CoV-2 transmission, infection outcomes, and immunity in residents and staff in long-term care facilities in England for adults aged 65 years and older since June 2020.
This analysis included long-term care facility residents undergoing routine asymptomatic SARS-CoV-2 testing between December 8, 2020 — the date the first vaccine was administered in the study cohort — and March 15, 2021 using national testing data linked within the COVID-19 Datastore.
This study was completed before the emergence of the Delta variant of SARS-CoV-2 now dominating in the UK.
The researchers estimated the reduced risk of PCR-positive infection at 0-6 days, 7-13 days, 14-20 days, 21-27 days, 28-34 days, 35-48 days, and 49 days and beyond after vaccination.
This was compared with unvaccinated residents, adjusting for age, sex, previous infection, local SARS-CoV-2 incidence, long-term care facility bed capacity, and clustering by long-term care facility.