A single Covid vaccine dose gives high levels of protection against severe disease, even in the oldest age groups, more evidence shows.
A study on patients in two Bristol hospitals found both Pfizer BioNTech and Oxford AstraZeneca jabs prevent 80% of hospital admissions among over-80s.
Some European countries are refusing to use the Oxford jab on older groups because of a lack of convincing data.
Lead researcher Prof Adam Finn said the findings should change their minds.
France agreed to offer the vaccine, which is easier to store than the Pfizer jab, to over-65s only recently, while Germany still isn't doing so.
"This study is much more important for non-UK countries than it is for the UK," said Prof Finn, who is running the study at the University of Bristol.
In the UK, this age group has now been immunised, he said.
"But there are lots of doses of AstraZenena vaccine available in European countries and they are not being given to people over the age of 65 - in some countries over the age of 55 - for lack of data.
"Well here are the data... showing that you can save lives in elderly people by giving them a dose of the AstraZeneca vaccine, and those countries need to get on and start doing that as fast as possible."
The Bristol findings support figures from other studies, including those run by Public Health England and Public Health Scotland, which looked at whole populations.
The England study found a 57% and 63% reduction in the risk of symptomatic infection in over-80s with the Pfizer and Oxford jabs respectively, 14 days after a single dose.
And both jabs reduced hospital admissions by more than 80%.
In Scotland, one dose of Pfizer appeared to provide an 85% reduction, and Oxford 94%, in admissions in this age group, over a slightly longer period - 28-34 days after a first dose.
But the researchers recommended not focusing too closely on small differences in numbers.
The studies look at slightly different things and all have fairly wide margins of error.
As more time passes and more people are vaccinated, more data will emerge, so these margins of error will shrink. This should allow scientists to be more confident in their estimates.
Oldest and frailest
The overall message from all the data coming out so far is both vaccines provide very good protection from illness.
This study was slightly different from the other two mentioned.
It focused on the oldest and frailest people at two major hospitals in Bristol, rather than looking at a whole population.
We would expect these people to respond least well to a vaccine, because their natural immunity is weaker.
And the researchers looked not at their chances of mild or moderate disease, as with other studies, but at how many vaccinated people still became severely ill and needed to go into hospital.
They were also able to look in more detail at patient records, including how long after having symptoms they were admitted to hospital.
This meant the team could identify and exclude from their sample people who had symptoms for more than 10 days before having a test, to reduce the chance of false negatives which could affect their findings.
'Real world' data
Vaccine clinical trials generally enrol younger people and measure whether any of them develop symptoms.
This is good at telling us how well that group is protected against mild and moderate disease.
But Prof Finn said what we really want to know is:
- How well the vaccines protect the oldest, and most at risk, from severe disease and death - the worst outcomes
- How much they stop young people from spreading the virus asymptomatically - keeping it circulating in the population
The Siren study of healthcare workers published last week suggests the vaccine stopped 70% of infections, even in those without symptoms, meaning those people could not transmit the virus.
Now, this Bristol study adds to our understanding of the first question - the biggest driver of loss of life and pressure on hospitals.
The study will continue for another two years to monitor the effectiveness of the vaccine on different groups.
For example, the team hopes to identify specific factors that "make people at increased risk of not responding well to these vaccines," said Dr Catherine Hyams.
That doesn't mean the vaccine will harm those people, but that those with compromised immune systems may not be able to benefit from the protection the jab is supposed to confer.
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