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Back from my holidays this week, and a chance to catch up on the latest swine flu situation at the weekly briefing at the Department of Health this afternoon. It looks as if we're approaching the end of the "first wave" of pandemic flu in the UK, with an official best estimate today of 11,000 new cases in England in the last week. This is a fall from the estimated 25,000 cases in the previous week, and 30,000 in the week before that. A quick look at the shows the rise and fall over the past few weeks of summer.

So what comes next? The Chief Medical Officer (CMO) for England, Sir Liam Donaldson, said it's "virtually impossible" to predict when the second wave might hit. He showed us the pattern in cases of previous pandemics. The pandemic of 1957- 58 saw a first wave peaking in late September/early October of 1957, and a second peak over Christmas and New Year of 1958. The pandemic of 1968-70 peaked first in early March 1969, then again over Christmas and New Year of 1970. "That's completely different to 1957-8, and nobody knows why," Sir Liam said.

Pandemic 2009 could look like either of those last two, he said, or do something entirely new of its own. He hopes we see no second wave until Christmas, because this would buy time in which to roll out the vaccine programme. And he clearly remains convinced there will be a second wave - whether sooner or later.

There's been some discussion while I've been away over the wisdom of giving antiviral drugs such as Tamiflu to otherwise healthy children who catch the H1N1 virus. One study suggested that side effects outweigh benefits, though this was based on seasonal flu not swine flu. And there was more to add to the "Tamiflu good-or-bad" debate from today's briefing. It emerged that on the basis of sample testing, officials estimate that only 10% of people reporting to their GPs and of those ringing the National Flu line actually have swine flu.

This has been higher, up to a maximum of 33% so the Health Protection Agency tells me. And they say that it's expected that the percentage would come down to about the 10% mark as we reach the end of a first pandemic wave. In fact it seems any rise in this number is a sign that a second wave has begun...so worth watching.

But if some 90% of those calling the National Flu line are likely to be swine flu free, it begs the question; how many callers are being prescribed Tamiflu when they don't actually need it? The Department of Health is getting back to me on that.

UPDATE:

I asked the Department of Health for numbers of callers being prescribed antivirals, and at the moment it seems to be just over 40%, down from close to 50% the week before. Here's what their spokesperson had to say:

"Use of the National Pandemic Flu Service has continued to fall. In the week ending 18 August, 108,555 assessments were completed and 45,986 courses of antivirals were collected. This compares to 192,007 assessments and 90,363 courses of antivirals collected during the week ending 11 August."