While infection risk is not eliminated, the vaccine still provided significant protection.
A recent study conducted by investigators from the University College London’s Institute of Health Informatics has discovered that a single dose of the Pfizer of AstraZeneca COVID-19 vaccine provided significant protection against disease in older adults.
Results from the study were published in the journal The Lancet Infectious Disease.
“The protective effect of a single dose of vaccination is evident from 4 weeks to at least 7 weeks after vaccination, which provides some evidence to support extension of the dose interval beyond 3 weeks, in line with UK policy,” the authors wrote. “However, even beyond 4 weeks, a single vaccine dose does not eliminate infection risk, highlighting the continued importance of non-pharmaceutical measures to control transmission within long-term care facilities.”
For the study, the team of investigators analyzed data from the VIVALDI study, which investigated SARS-CoV-2 transmission, infection outcomes, and immunity in residents and staff in long-term care facilities in England.
The study included 10,412 participants who were 65 years or older from 210 long term care facilities.
Of the participants, 9,160 received at least 1 dose of vaccine, which included 6,138 receiving the AstraZeneca vaccine and 3,022 receiving the Pfizer vaccine.
Findings from the study showed that between December 8, 2020, and March 15, 2021, there were 1,335 PCR-positive infections, of which 713 were in the unvaccinated residents and 612 in the vaccinated residents.
Adjusted hazard ratios for PCR-positive infection relative to unvaccinated residents declined from 28 days after the first vaccine dose to 0.44 at 28 to 34 days and 0.38 at 35 to 48 days. Both of the vaccines showed a similar effect size at 35 to 48 days.
“Further work is required to evaluate the effectiveness of the second dose of the vaccine, and the effect of vaccination on transmission,” the authors wrote. “This knowledge will be critical to inform policy decisions regarding revaccination schedules in this vulnerable population and the disease control measures needed in the short, medium, and long term to protect long-term care facilities from future waves of SARS-CoV-2 infection.”