A single dose of a coronavirus vaccine is up to 80% effective at preventing complications severe enough to require hospitalisation among the elderly, research suggests.
The UK has three approved vaccines in its immunisation arsenal, two of which are being rolled out – Pfizer-BioNTech and University of Oxford-AstraZeneca.
Both jabs were approved as two-dose regimens, with an interval of three to four weeks between the vaccines being administered.
To maximise the number of people being immunised, the UK's vaccination strategy is focusing on giving more people a first dose, with the second jab's administration recommended 12 weeks later.
This approach is increasingly being supported by real-world data, with scientists from the University of Bristol estimating that a single dose of the Pfizer-BioNTech or Oxford-AstraZeneca jab is 79% or 80% effective, respectively, at warding off complications severe enough to require hospital care 14 days later in people aged 80 or over.
The results are preliminary and yet to be published in a peer-reviewed journal.
"We are very pleased to share these early results that show the UK COVID-19 [the disease caused by the coronavirus] vaccine programme is working better than we could have hoped," said lead author Professor Adam Finn.
"We are also delighted our findings could reduce the burden of serious illness in our elderly population and relieve the pressure on the NHS.
"The study will continue to provide further and more detailed information as time goes on."
The Pfizer-BioNTech and Oxford-AstraZeneca vaccines were approved after demonstrating 95% and 70% efficacy against severe disease, respectively, in clinical trials. These were not made up of elderly, frail volunteers, however.
A lack of efficacy in older populations prompted some European officials to advise against the use of the Oxford-AstraZeneca jab among the elderly, a move that has been criticised by UK scientists and politicians alike.
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The Bristol scientists analysed data collected by the Pfizer-funded surveillance project AvonCAP.
This records detailed information on every patient admitted to Bristol's two large NHS hospitals with medical complications or X-ray evidence of diseased lungs, caused by the coronavirus or another condition.
Between 18 December 2020 – 10 days after the UK's coronavirus vaccination programme began – and 26 February 2021, 434 eligible patients were noted, all aged 80 or over.
Many of the patients were frail with underlying health conditions, making them particularly vulnerable to complications and therefore in need of an effective vaccine.
The scientists compared vaccination rates between those with acute respiratory disease who had a positive or negative coronavirus test upon admission, before estimating the effectiveness of one vaccine dose.
Results suggest one Pfizer-BioNTech dose was 71% effective at preventing illness severe enough to require hospital care 14 days after the jab was administered.
A single Oxford-AstraZeneca vaccine was found to be 80% effective.
With the vaccines being rolled out almost a month apart – Pfizer-BioNTech on 8 December and Oxford-AstraZeneca on 4 January – the scientists then reconciled the data to cover the same time period in early 2021.
These results suggest a single dose of either vaccine is almost identical in effectiveness, at 79% for Pfizer-BioNTech and 80% for Oxford-AstraZeneca, after 14 days in people aged 80 or over.
The scientists accounted for other factors that influence an individual's risk of coronavirus complications and their availability of a vaccine, like their sex, whether they live in a care home and their degree of social deprivation.
The overall results are reasonably similar to recent real-world studies carried out elsewhere in the UK.
A Public Health England trial suggested one dose of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine in people aged 80 or over reduced the risk of hospitalisation by 43% and 37%, respectively, after more than 14 days.
These studies linked large databases of test results, immunisation records and diagnostic codes for entire populations.
The Bristol scientists, however, drew on a "comprehensive and detailed examination of all medical admissions in two admitting hospitals in a single city".
"This means the dates of onset of symptoms could be accurately recorded and included in the analysis, and compensation made for possible biases due to rapid changes in the vaccine rollout and the transmission of [the coronavirus] that occurred during the last three months," according to the Bristol team.
"By providing corroborating evidence using a different methodology, the research team provide reassurance the conclusions now being drawn about the short-term effectiveness of one dose of these two vaccines is valid."
The scientists believe their results are applicable outside of the UK and may help other countries developing immunisation strategies to protect their vulnerable, elderly residents.
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