National Health Service (NHS) England said the program was brought forward based on the latest expert advice.
Flu vaccines are available to all, while Covid vaccines will be offered to eligible groups including care home residents, over-65s, front-line health and social care workers and those at clinical risk.
Winter vaccination campaigns also begin this month in Scotland and Northern Ireland, with Wales starting last week.
The U.K. began to investigate a Covid variant with multiple genetic differences to its predecessors, BA.2.86, in August after it was linked to a "high attack rate" in an outbreak at a care home.
The U.K. Health Security Agency also said there was insufficient evidence to link it to early indicators of increased Covid-19 transmission in the U.K., or to judge its severity.
Organizations:
Monday, National Health Service, NHS, Royal Pharmaceutical Society, Wales, Health Security Agency
Locations:
England, Scotland, Northern Ireland