The UK may be experiencing a "lucky break" as the rate of swine flu spread slows, the chief medical officer has said.
Sir Liam Donaldson said the second wave of the flu pandemic was well under way but current figures suggest the expected peak could be lower than previously thought.
Estimates show there were 18,000 new cases of swine flu in England in the last week, up from 14,000 in the previous week and 9,000 the week before that.
The rate of increase is nowhere near the weekly doubling experts feared.
Sir Liam said: "We are well into the second wave of pandemic flu, having had the first wave in July but it's proving so far to be a slow burner.
"It's possible that it might peak at a lower level and an earlier level than expected which would be incredibly positive news.
"It means we could get the vaccine programme well under way.
"If this virus has another peak or third up its sleeve as in 1968 we might be able to avert that completely."
He said viewing past pandemics through 20th century eyes the number of cases could be viewed purely in terms of statistics.
However looking at the current pandemic through 21st century eyes "every death is a person not a statistic and we should be fighting it all the way", he said.
Sir Liam added: "We may have got a lucky break in how the virus has behaved at the start of our flu season and we may be able to get the vaccine out there before our flu season really gets under way.
"I'm looking at it very optimistically."
The Government is still awaiting deliveries of the GlaxoSmithKline (GSK) vaccine but it is hopeful that the first doses will be given to priority groups and frontline health workers at the end of the month.
Sir Liam said around half a million doses of the Baxter vaccine were in stock and no GSK had arrived yet but it was "imminent".
Asked why the rate of increase in the number of swine flu cases may be slowing down, Sir Liam said there may be herd immunity among over 65s from a 1950s strain of the flu.
Schoolchildren may also have a degree of immunity against the current strain due to exposure, he added.
The UK number of deaths linked to swine flu currently stands at 90, with 76 in England, one in Wales, 10 in Scotland and three in Northern Ireland.
There are currently 290 people in hospital in England, of which 47 are in intensive care.
Sir Liam said the number of people in intensive care was the highest figure for the last two months. He said this was a "bit of a concern".
