By Nick Triggle
Health reporter, BBC News
The majority of cases in the UK have shown only mild symptoms
The UK may have had a "lucky break" with the way swine flu is spreading, the chief medical officer says.
The number of new infections has dropped in Scotland and is not rising as rapidly as first feared in England.
Sir Liam Donaldson said the second peak was proving to be a "slow-burn" which was buying time to get the vaccine programme under way.
The two jabs being used in the UK have now been licensed and GPs should start immunising within a few weeks.
By getting to that stage before a sharp rise in new infections, Sir Liam believes many lives could be saved.
"We are well into the second wave of pandemic flu after the first wave in July, but it is proving to be a slow-burn.
"We may have got a lucky break with the way the virus has behaved and we may be able to get the vaccine out there before our flu season really gets under way.
"I am looking at it very optimistically."
People with underlying health conditions, such as heart disease and diabetes, and pregnant women will be among a 14m-strong priority group which will get the vaccine first along with health workers.
The government has yet to decide whether the rest of the population should be vaccinated.
Sir Liam even suggested the second peak may not be as bad as first anticipated.
"It is possible it may peak at a lower and earlier level than first expected. That would be incredibly positive."
Sir Liam was speaking after releasing the latest figures for weekly infections.
In England, there were 18,000 new cases - up from 14,000 the week before - but well short of the doubling that would represent a surge in cases.
However, the number of patients in intensive care has hit 47 - a two-month high
Meanwhile, in Scotland the number of new infections has halved to 6,800.
Numbers of cases in Wales and Northern Ireland have always been and remain much lower. However, the rate of infections in Northern Ireland has started to accelerate sharply.
In total, 90 people have died with swine flu since the outbreak first started.