Chris Whitty has warned "very sick" young adults "regret delaying" their coronavirus vaccines after working in a COVID-19 ward for the past four weeks.
England's chief medical officer, who is the UK's most prominent COVID scientist, wrote on Twitter on Friday of his personal experience on the ward.
He said: "The great majority of adults have been vaccinated.
"Four weeks working on a COVID ward makes stark the reality that the majority of our hospitalised COVID patients are unvaccinated and regret delaying.
"Some are very sick including young adults. Please don't delay your vaccine."
The latest government statistics show that as of Thursday, 87.4% of UK adults had received a first jab while 76% are double-jabbed.
However, vaccination rates among young adults remain significantly lower than in older people, as this government heat map showing uptake in England demonstrates. The lighter the shade of blue, the lower the uptake.
Uptake in the 18 to 24 group is 63.6%, the figures show, while it's 62.2% for the 25 to 29 group.
Separate data published by the UK’s four health agencies on Thursday estimated 2.9 million 18 to 29-year-olds are unvaccinated.
Concern over the slowing of vaccine uptake among younger people prompted Boris Johnson to say that from September only those who had had two doses of a coronavirus vaccine would be allowed entry to crowded venues such as nightclubs.
But Prof John Drury, of the University of Sussex, a participant in Spi-B, the Sage subcommittee advising on behavioural science, said: “Incentivisation will work for some but will backfire with those who are most hesitant and suspicious, who will perceive it as coercion.”
Prof Whitty's comments, meanwhile, came as new figures showed 55% of people in hospital with the Delta variant – which is dominant in the UK – have not been jabbed.
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The data from Public Health England also show 74% of people under 50 in hospital with the variant had not been vaccinated.
Almost two-thirds of people in the same age group who died in England with the Delta variant were not vaccinated against the virus, the figures show.
Meanwhile, data published by the Office for National Statistics (ONS) on Friday suggested the majority of Britons (87%) would be likely to have a booster vaccine if offered.
Health secretary Sajid Javid said on Thursday he is “confident” a booster campaign can start next month.
NHS plans are in place to enable a rollout of third doses of jabs from 6 September alongside flu vaccines – though no official decision has been taken yet.
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