New Government figures show swine flu vaccinations have been given to more than a million people at high risk from the virus in the first month of the programme.
Doctors are currently giving the vaccine to those who suffer from conditions such as asthma, heart disease and diabetes - before moving on to the under-fives.
About a million people in England and thousands more in Scotland, Wales and Northern Ireland have received their jab.
The figures come as the number of people catching swine flu in England appears to be falling. There were an estimated 46,000 new cases in the last week, down from 53,000 in the week before.
There has also been a drop in the number of people in hospital, from 783 to 753. A total of 154 of those currently in hospital are in intensive care.
The number of deaths counted in a single week, however, is at its highest - with 21 deaths confirmed in England in the last seven days. The number of deaths in England now stands at 163, up from 142, and the UK total stands at 242, up from 214.
One million equates to about one in 10 of all the people in at-risk groups who are being offered the vaccine.