Dr Roland Salmon, director of the Communicable Disease Surveillance Centre at the National Public Health Service for Wales (NPHS), urged people to get vaccinated after it emerged five patients at a hospital in Cardiff have been diagnosed with a strain resistant to antiviral drug Tamiflu.
Dr Salmon said: "Vaccination is the most effective tool we have in preventing swine flu so I urge people identified as being at risk to look out for their invitation to be vaccinated by their GP surgery.
He said cases in Wales were declining, despite the five cases at University Hospital of Wales.
"The number of people contacting their GP with flu symptoms has stalled and started to decline slightly over Wales as a whole," he said.
"Nevertheless flu is still circulating and we therefore continue to emphasise the importance of being aware of the symptoms of swine flu and of the steps that can be taken to prevent its spread.
"The vaccine against swine flu has been tested and approved. It is now being offered to people at most risk of complications from the virus as well as front line health and social care workers.
"People with flu-like symptoms should stay at home, observe good respiratory and hand hygiene and stay away from GP surgeries, Accident and Emergency departments and pharmacies unless advised to do so, which will also help to limit the infection's spread.
He added: "If symptoms worsen or people have underlying health problems they should call their GP.
"Most people make a full recovery from swine flu without needing to be admitted to hospital or to call a doctor. However, a few people go on to develop complications and as the pandemic continues we are seeing deaths from swine flu in Wales, just as we do most years from seasonal flu."
