By Jane Dreaper
BBC News, health correspondent
Firms are hard at work on a vaccine
The number of swine flu cases in the UK has climbed to more than 330.
The Health Protection Agency recorded more than 60 new cases alone on Tuesday, and although nobody has yet died from the virus, experts are warning against any complacency.
And the hard work is only just beginning for scientists developing a vaccine.
At the west London office of the drug giant GSK, there is a special unit for global planning on flu pandemic vaccines.
A special sample of the swine flu or H1N1 virus has arrived at GSK in the past week, allowing scientists to begin a detailed analysis.
The UK medical director, Dr Pim Kon, told me the six-month process has many uncertainties.
Although the company has agreed to provide 60m doses of a vaccine, it is not yet known how many people that will cover.
Dr Kon said: "That is still to be determined, as it is based on how the production goes.
"The scientists will also be keeping a very close eye on whether the virus mutates.
"The vaccine will be based on certain parts of the virus, so they'll need to see whether those parts change."
The detailed scientific work is being done at GSK's plant in Belgium, while executives in London negotiate global contracts.
Health experts are monitoring H1N1 cases in countries like Brazil, where winter and normal "seasonal" flu is just beginning.
Professor Ab Osterhaus, who is based in Rotterdam, has studied flu viruses for half of his 30-year career, and predicts various tensions in the months ahead.
He said: "If you start to produce the pandemic flu vaccine, it will go at the cost of the seasonal flu vaccine.
"Seasonal flu kills between 250,000 and 500,000 people around the world every year - so we still have a responsibility there as well.
If we have a pandemic, there'll be a problem with equitable distribution of these protective measures
"The production capacity is limited, and vaccines have to be produced within six months.
"There is likely to be competition between countries.
"The richer countries have ordered pre-pandemic vaccine. That is not the case for countries that don't have so many resources.
"So if we have a pandemic, there'll be a problem with equitable distribution of these protective measures.
"It's a major issue for the World Health Organisation to consider."
The Scottish health secretary, Nicola Sturgeon, has warned that H1N1 may be spreading in the community - despite efforts to contain it among known travellers and their contacts.
Previous pandemics have started in a mild fashion, but developed in waves.
And although the figures do not now lead news bulletins, the number of swine flu cases continues to rise each day.
After the initial flurry of coverage, questions were raised about whether the threat posed by H1N1 had been over-hyped.
That is firmly denied by the health editor of the Independent newspaper, Jeremy Laurance, who wrote a strident front-page piece a month ago.
He told me: "People say there are only two kinds of medical story - the miracle cure and the deadly scare.
"You wait 20 years for a proper scare to come along - and when one does, people accuse you of crying wolf.
"I felt there was a real need to answer that charge - and that's why I wrote the piece I did.
"This is a wholly new virus that we haven't seen before.
"And it's estimated a third of the world's population won't have immunity to it.
"That's why we need to take it seriously."
And in the meantime, the NHS is learning lessons.
A leading light in the BMA doctors' union, Dr Jonathan Fielden, works in intensive care at a busy hospital in the Home Counties.
Dr Fielden said: "We had a case of concern which led us to ensure we had special masks which were properly fitted.
"They give a higher level of protection than the masks we use in theatre.
"So far, it's been a useful test of our procedures, in circumstances where the flu hasn't been severe at this stage.
"Our concern, as we come to the normal flu season in the winter, is that many of our resources are already under pressure.
"Although there's been an increase in intensive care beds, we still have some of the lowest numbers in Europe per head of population.
"Those beds are often under great stress in normal circumstances - and in these circumstances, there will be pressure throughout the system."