SCOTLAND is facing a new wave of swine flu, which experts warned could claim more lives than last year's.
The NHS will unveil a campaign next week to vaccinate thousands of Scots in response to fears the virus will return this winter in a more virulent form.
Swine flu killed thousands around the world last year - including more than 60 in Scotland - before it receeded.
But experts who have studied the spread of previous global flu epidemics fear swine flu might follow the example of other pandemics and make a deadly return.
The NHS confirmed that doctors are worried about the re-emergence of swine flu.
A spokesman said: "It is expected that H1N1 will be the main flu virus circulating during the 2010-11 season.
"Most people will recover from flu naturally within a week. However, those with health conditions, including heart and lung problems, are at an increased risk of experiencing serious complications as a result of flu.
"These people, including children, are encouraged to receive vaccination to protect themselves."
The NHS seasonal vaccination programme begins on 4 October. Officials have made H1N1 the "predominant" presence in the new vaccine, which also contains two ordinary flu strains which experts expect to be active this winter.
The injections will target over-65s, under- 65s with underlying health complaints, pregnant women and frontline NHS workers.
Officials confirmed they expect swine flu to be "circulating in communities throughout the winter".
Health experts say every pandemic in history has been followed by more serious waves.
Professor Hugh Pennington, Professor Emeritus of Bacteriology at Aberdeen University, said: "The past is the guide to the future with flu and with all pandemics there have been subsequent waves which have been hotter and nastier and killed more people.
"In 1918-19, for example when 50 million people died of H1N1, the second wave was much more serious than the first.
"A lack of scientific evidence means we do not know and are never likely to know whether this was because of a mutation or because it attacked people who were not affected first time round.
"Viruses just don't behave themselves and it is reasonable to expect a return of swine flu. One other possibility is that we might get another flu virus which is a sort of mutation because different viruses, including H1N1, have bred their genes between them.
"That can lead to a genetic change in the virus that means it is just a bit hotter and can be just a bit more lethal.
"The problem is we just don't know what the rules are but a return of swine flu during the winter months must not be ruled out."