People in Wales at risk of contracting swine flu have been urged to get vaccinated against the virus after it emerged five people have been diagnosed with a strain resistant to Tamiflu.
The advice came from Dr Roland Salmon, director of the Communicable Disease Surveillance Centre at the National Public Health Service for Wales (NPHS).
He was speaking after it was announced five patients at University Hospital for Wales in Cardiff have been diagnosed with a strain resistant to the antiviral drug.
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."
More than three million healthy children under five across the UK are also to be offered the swine flu jab, it was announced earlier this week.
Parents will be invited by their GPs to bring their children into surgeries, with vaccinations expected to start in December.
The Tamiflu-resistant strain will become much more common as the virus mutates, according to a flu expert.
Three out of the five patients diagnosed at the University Hospital for Wales remain in hospital, after it was revealed they could be the world's first cases of person-to-person transmission of the virus, the NPHS said.
Professor Nigel Dimmock, a virologist at the University of Warwick, said: "This is just the beginning. You have got a lot of viruses and if you use Tamiflu at the level they are using it you get resistance.
"However, they probably aren't resistant to Relenza, the other anti-viral. You need other mutations to make it resistant to Relenza. Also, the vaccine is coming on so people regard Tamiflu as a stop gap and there's no need to panic."
