Six million doses of influenza vaccine are currently on their way to GPs, but if you're relatively young and healthy, don't bank on having one: they are earmarked for people who really need them. Flu kills about 3,000 to 4,000 people in the UK each year, most of them 65 and over, and already weakened by illness.

Healthy people who contract a flu virus usually get away with a week of hell followed by another of tottering frailty - but one bout of flu gives immunity, so there is the consolation of knowing one is unlikely to go down again with that particular strain for three years or so. Vaccination reduces the likelihood of getting flu by 60 to 70 per cent but it gives immunity for only a single year. Each jab costs more than pounds 5 so, to make vaccination cost-effective for the NHS, GPs are currently advised to offer it only to patients for whom a bout of flu is likely to cause serious medical problems. These include people with lung, heart, kidney and immune function disease, and elderly or other vulnerable people living in residential institutions. In the past about one in four flu jabs have gone to people outside the high-risk categories, so this year the Department of Health is trying to cut out these non cost-effective treatments by discouraging the "worried well" from badgering their GPs for vaccines.

In the US, where most vaccines are paid for privately, the authorities recommend that everyone has a flu vaccine, citing evidence that vaccinating healthy people is actually the best way to protect the unhealthy, too, since it reduces the general prevalence of the virus. Research also shows that people who have a flu shot reduce the time lost from work through illness by 43 per cent.

Supplies are constrained because each year's vaccine has to be manufactured to order. Vaccine cannot be held over from year to year; new strains of virus emerge and old ones ebb and flow. This year, for example, the World Health Organisation predicts that we will be hit by a new strain called Wuhan. Named after the province in China where it was first identified, Wuhan causes a typically achey, cough-and-wheeze illness. The 1996/7 vaccine includes the Wuhan strain plus two previous ones, Singapore and Beijing - both of which are now predicted to make a comeback.

If you are a high-powered executive, a hard-pressed working mother or just someone who has booked a nice holiday and doesn't want it ruined, you could try pleading with your GP, or even offer to pay for a flu shot, but this won't help the vaccine supplies and you'll probably be asked to go to the back of the queue. It takes two or three weeks for resistance to build up after the vaccination, so if you are determined to avoid the Wuhan peril you should talk to your doctor about it now rather than waiting for the peak flu time in the new year. Some people say they feel rough for a day or two after vaccination, but the virus is inactivated before it is injected, so - despite common mythology - it cannot give you flu.