Single dose of Pfizer, AstraZeneca vaccines offers 60 percent protection
A single dose of Pfizer or AstraZeneca COVID-19 vaccine offers around 60 percent 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 in the UK used data from the VIVALDI study.
Research investigated SARS-CoV-2 transmission in long-term care facilities
That research investigated the 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.
Study was completed before the emergence of Delta variant
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.
Risk of infection at various intervals was analyzed
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 the long-term care facility.
The analysis included 10,412 care home residents
The analysis included 10,412 care home residents aged 65 years and older from 310 facilities, with a median age of 86 years, of whom 70 percent were female and 1,155 residents (11 percent) had evidence of previous SARS-CoV-2 infection.
Efficacy rate increased as more days passed after first dose
A total of 9,160 (88 percent) residents received at least one vaccine dose during the study period, of whom 6,138 (67 percent) received AstraZeneca and 3,022 (33 percent) received Pfizer. The risk of infection was 56 percent lower in the vaccinated residents after 28 to 34 days, and 62 percent lower at 35 to 48 days.