Symptoms of swine flu also appear in other diseases
A swine flu vaccination campaign will be launched in Northern Ireland this autumn, but only certain at risk groups will be given the jab.
Those with underlying health conditions up to the age of 65 have been identified as the first priority, followed by pregnant women.
Health and social care workers will also get the jab.
Health Minister Micheal McGimpsey said his department had yet to decide whether everyone should be given it.
"There has been a noticeable decrease in swine flu cases across the UK. In Northern Ireland, figures remain higher than normal for the time of year but are now showing slight reductions," he said.
"While the figures may be decreasing, it is expected that there will be a surge of cases in the autumn and it is essential that our population is protected."
England's Chief Medical Officer, Sir Liam Donaldson, said the vaccine was going through similar safety testing as the seasonal flu vaccine.
He added: "We have a real chance to save lives if we can get the vaccine in place.
"We are putting up a real fight against this virus."
The vaccine programme is due to roll out as follows if it is granted approval by European regulators in late September or early October as expected:
• In October, those aged six months to 65-years-old in conventional at-risk groups for normal seasonal flu, such as those with diabetes or heart disease, will be vaccinated.
• This will be followed by all pregnant women, subject to licensing arrangements and better information on when in the pregnancy the vaccine should be given.
• People living in households with patients with suppressed immune systems and those over 65 in conventional at-risk groups will then be eligible.
• Front-line health and social care workers will then be vaccinated.
• By the middle of winter, the government hopes to have enough evidence to decide whether the campaign should be extended to healthy people.
Many people had expected children to be among the first wave of priority groups.
But experts ruled this out because while they have been the worst hit in terms of the number of cases it is mainly those with underlying health conditions that have developed complications.