Some 42% of people admitted to hospital in England the last month were unvaccinated, despite people who haven't had a single dose making up only 19% of the population, according to data from the UK Health Security Agency (UKHSA).
It comes after health secretary Sajid Javid hit out at people who have chosen not to have their vaccine, accusing them of "taking up hospital beds".
Speaking on Wednesday, former prime minister Tony Blair called people who had turned down a COVID jabs "idiots".
Data covering the period between 15 November to 12 December shows that unvaccinated people accounted for a high percentage of hospital admissions, relative to the proportion of each age cohort which was not vaccinated.
In this analysis, 'vaccinated' means a person has had at least two doses, and 'unvaccinated' means they have had no doses.
Among over 80s, 18% of those hospitalised with COVID were not vaccinated, despite making up just 4% of this age group.
For 18-29 year-olds, 63% of those admitted to hospital with COVID were not vaccinated, while 38% of this age-group have not had a jab.
Read more: How to book your COVID booster jab
During the same time period, the rate of people hospitalised with COVID among unvaccinated people was higher than among the vaccinated, with the difference becoming more pronounced in older age groups.
The hospitalisation rate among unvaccinated over 80s was 181 per 100,000 people, almost five times the rate among the vaccinated at 36.8 per 100,000.
The government is attempting to significantly ramp up the speed of the COVID booster vaccine campaign in the run-up to Christmas in the hope of curbing the spread of Omicron.
Boris Johnson has pledged not to introduce new curbs ahead of Christmas, but new measures after Christmas Day are still a possibility.
The PM said he has so far not seen enough evidence on the severity of the Omicron variant and hospital admissions to justify stricter measures.
Watch: No new COVID restrictions before Christmas, Boris Johnson says
On Wednesday morning, one minister hinted at coming restrictions.
Health minister Gillian Keegan told LBC: “There is uncertainty. We can’t predict what the data is going to tell us before we’ve got the data.
“We are trying to take a balanced and proportionate approach so that people can see their families over Christmas to try and plan some stuff.
“But of course it is difficult to anticipate.”
Elsewhere, it was reported that Government scientists are set to conclude that Omicron is causing a milder disease than Delta strain in most Britons, but its transmissibility is such that hospitalisations may still hit an unmanageable level.
Politico said the UKHSA is expected to publish early real-world data on the disease’s severity before Christmas.
A UKHSA spokesman said the agency said it is still conducting analysis on Omicron and data will be published later this week.
He said: “We are reviewing all analyses continuously to help inform the pandemic response, which includes assessing the severity of Omicron.
“We will publish these latest findings in the variant technical briefing on December 23.”