It had to happen sooner or later and now it has. As the world prepares its defence against the first flu pandemic for more than 40 years, a gap has opened up in the strategy to defeat the virus adopted on either side of the Atlantic.
In the UK we are going with adjuvanted vaccines – that is, vaccines with a chemical added to boost the immune response so that less viral material is needed for each vaccine dose. The European Medicines Evaluation Agency, which approved the first vaccines last week, said adjuvants were widely used in vaccine manufacture and had a good safety record.
The US, however, has rejected the use of adjuvants because they think they raise an extra, needless worry just at the time when they are trying to persuade as many people as possible to accept the jab. Jesse Goodman, chief scientist at the US Food and Drug Administration, said: "These are products that potentially can be given to millions of healthy people. There is not a known, specific safety danger or issue. There is just more uncertainty."
The US has form on this matter, which accounts for their greater sensitivity. In 1976, there was an outbreak of swine flu on a military camp in New Jersey. Around 200 soldiers fell ill, and one died, triggering a nationwide panic. A mass vaccination programme was rolled out and 40 million Americans received the jab in three months. The swine flu fizzled out, but allegations followed that the vaccine caused more harm than the disease, including 20 cases of Guillai-Barre Syndrome, a serious neurological condition. This has since been challenged – but the taint remains.
The problem that is now facing public health specialists on both sides of the Atlantic is that swine flu is a mostly mild illness, but in a small minority – chiefly the young and/or pregnant women, in contrast to seasonal flu which targets elderly people – it can be serious and even life-threatening.
As most people perceive it as a mild illness, enthusiasm for vaccination is low. A poll last week by the University of Michigan in the US found that just 40 per cent of parents said they would have their children vaccinated. In the UK, a poll earlier this month by the website Mumsnet.com found that half of the pregnant women who responded said they would refuse the jab.
So the omens are not good. But this is early days. How the public chooses to view swine flu vaccine once it is actually offered to them will be fascinating.
On the one hand, they may take the line of the MMR refuseniks, protesting that swine flu, like measles, is a mostly mild illness and that any risk at all from the vaccine – even though based on discredited allegations – is not worth running.
On the other hand they may welcome it, like the meningitis C vaccine, which saw a 90-plus per cent take up within months of its launch in 1999. Meningitis has the virtue, in this context, of always being nasty. It doesn't do mild.
Yet of one thing we can be confident – swine flu will kill more people this winter than meningitis. If the jab comes my way I shan't hesitate to have it.