There were 9,472 people admitted to hospital with the highly transmissible Delta variant in the seven days up to August 29, Public Health England (PHE) data showed.
Some 5,098 were under the age of 50. Figures show 3,742 (73 per cent) were unvaccinated, while 724 (14 per cent) had received just one dose.
PHE said 521 or 10 per cent of patients had received both Covid jabs.
More than 90 per cent of over-50s in England have now been fully vaccinated, according to the NHS data.
Among the 4,374 admitted to hospital who were aged 50 or over, 30 per cent were unvaccinated, nearly nine per cent had received one jab and 61 per cent had been given their second jab.
In the same time period, a total of 1,798 people who had the Delta variant died, PHE said.
The Delta variant has become by far the dominant strain in the UK and makes up almost all of new infections.
The Government has been urged to “get on” with the vaccine booster programme and give the vulnerable and elderly a third jab as quickly as possible.
Prime Minister Boris Johnson and the Health Secretary have suggested a rollout will begin this month, with older people prioritised as winter approaches.
However, the Joint Committee on Vaccination and Immunisation (JCVI) has not yet provided an official recommendation on boosters for the wider population.
But a final decision has not been made.