Thai authorities closed hundreds of schools across the UK for disinfecting, as the health ministry reported three more swine flu-related deaths, bringing the country's total to 24.
The news came after the World Health Organisation (WHO) said on Monday that a fully licensed swine flu vaccine might not be available until the end of the year, a scenario that could affect many countries' vaccination plans.
Thailand's Prime Minister Abhisit Vejjajiva spoke on national television to urge people not to go to work or school if they had any symptoms of flu, in a bid to stem the growing number of people in the country contracting the H1N1 swine flu virus.
A Public Health Ministry spokesman said the latest victims were a 67-year-old woman and a 57-year-old woman in Bangkok and a 32-year-old woman in central Samut Sakhon province.
All three had underlying medical problems before contracting the virus, making them more susceptible, the spokesman said.
On Monday, the director of WHO's Initiative for Vaccine Research, Marie-Paule Kieny, said it could take until the end of 2009 for a vaccine against the virus to be properly licensed.
She said the vaccine would be available in the next couple of months, but it would need to undergo clinical trials for safety and to determine the dosage, which would take some time.
But countries could use emergency provisions to get the vaccines out quicker if they decided their populations need them, she said.
Kieny said different countries would be in different stages of epidemic with regard to the virus, and would need to make plans based on their own individual situations.
Britain is the hardest-hit nation in Europe, with health authorities reporting that 17 people have now died after contracting the virus.
The UK's Press Association news agency reported there have been almost 10,000 confirmed cases of swine flu in Britain, but hundreds of thousands more people are thought to have the virus.
British health authorities announced on Monday that a family doctor and a six-year-old girl had died after contracting swine flu.
The National Health Service said Doctor Michael Day, who was from Dunstable, in the county of Bedfordshire, had died in hospital over the weekend.
Elsewhere, six-year-old Chloe Buckley died in a London hospital on Thursday after contracting the virus.
St Catherine's School in West Drayton, just north of London, where the 6-year-old was a student, has temporarily closed.
UK broadcaster Sky News showed parents arriving at the school on Tuesday and being handed information leaflets.
British Health Secretary Andy Burnham promised that vaccines would start arriving in the UK in August - and predicted the country could see up to 100,000 cases a day by the end of that month.
Before countries can start any mass swine flu vaccination campaigns, the vaccines need to be vetted by regulatory authorities for safety issues.
That means testing the vaccines in a small number of humans first, which can take weeks or months.
The swine flu viruses currently being used to develop a vaccine aren't producing enough of the ingredient needed for the vaccine, and WHO has asked its laboratory network to produce a new set of viruses as soon as possible.
So far, the swine flu viruses being used are only producing about half as much "yield" to make vaccines as regular flu viruses.
In a presentation to WHO's vaccines advisory group last week, Kieny said a lower-producing vaccine would significantly delay the timeline for vaccines.
That could complicate many Western countries' plans to roll out vaccines in the autumn.
Kieny said many of those questions remain unanswered at the moment.
But she said WHO's vaccine advisory group recommended that health care workers receive the first swine flu shots since they are on the front lines of the global outbreak.
WHO's vaccine experts recommend that countries decided that certain groups should get the vaccine first - like pregnant women, people with chronic respiratory problems or obesity, children, and possibly young to middle-aged adults, who have been disproportionately affected by the virus.
The decision to start vaccinating people against swine flu - which so far remains a mild virus in most people - will ultimately be a gamble, since there will be limited data on any vaccine.
Until millions of people start receiving the shots, experts will not know about rare and potentially dangerous side effects.
Last week, the World Health Organisation reported nearly 95,000 cases of swine flu worldwide including 429 deaths.
Most people who get the virus only experience mild symptoms and don't need treatment to get better.
AAP