No appointments are needed for the Covid vaccines at the Yorkshire Events Centre site, which has extended its offer after reopening earlier this week with some walk-in availability.
Those eligible must have had their second jab more than three months ago.
This gap between vaccines was originally six months but has been reduced after advice from the government's scientific advisers and in response to the new Omicron variant.
The showground was used as a vaccine site earlier in the year and has set an aim of delivering 20,000 jabs before it had planned to close on 22 December.
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However, it now looks set to stay open for longer as part of the boosters push.
Heather Parry, managing director of the Yorkshire Event Centre, said talks are being held with the NHS and that it was now "finalising details" for an extension of the site into the New Year.
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Meanwhile, appointment-based vaccines are still available to book online through the NHS booking service.
It comes as Prime Minister Boris Johnson last night announced new measures in response to the Omicron variant.
Rules on face masks have been extended with a requirement for them to be worn in most public settings, including theatres and cinemas, from Friday.
From Monday, people will be asked to work from home where possible
And the NHS Covid Pass - proving vaccination status or a negative lateral flow test - will also be required for visitors to nightclubs, indoor unseated venues with more than 500 people, unseated outdoor venues with more than 4,000 people and any event with more than 10,000 people from Wednesday.
By Jacob Webster, Local Democracy Reporter