Calum Semple, of the University of Liverpool, who co-led the study, said: “This is a story about vaccine success.
“When we looked at the early data … it was a moment of joy, and the re-analysis of a greater number of patients is very reassuring, it does show the biology of the vaccine working in this high-risk group.”
The findings follow a major study this week showing that just one dose cuts the risk of onward transmission by up to half among those who become infected with Covid despite having been vaccinated.
The new study tracked 52,280 people hospitalised with the virus during the second wave, between the start of the vaccine rollout on Dec 8 and April 10.
They included 3,598 people who had received a jab, with data tracking the timing of it. This showed the vast majority were patients who became infected just before getting their vaccine, or too soon after for immunity to develop.
Just 526 were patients who had received a first jab at least three weeks before, the time required to build protection – a rate of one per cent. They included 113 patients who died, a rate of 0.2 per cent, with the vast majority of deaths occuring in those over the age of 80.
Prof Semple said the analysis was designed to give Sage “a very early signal on whether vaccines were working in the real world”, adding: “The absolute numbers of people being admitted to hospital after 21 days of the first dose is tiny.
“It is very small, but it does occur – it is mostly occurring in the group most at risk of severe disease, which is the elderly, people who are very frail and very old. This is good real-world evidence of it working, but there are some few failures. And when these failures do occur, sadly, people die, but that is because they are elderly and frail.”