As flu can be caused by any of hundreds of strains of myxovirus, which mutate more or less constantly, vaccination amounts to a kind of biological Russian roulette. Even if the vaccine is for the right strain of myxovirus, for reasons not yet fully understood, you may not respond by producing anti-bodies to it. One study found that 30-40 per cent of elderly people do not respond to vaccination (Hum Immunol, 1994; 40: 202-9), and even if an immune response occurs, there is doubt as to whether this reduces the incidence of influenza (Vaccine, 1994; 12: 1185-9).

Studies into the efficacy of the flu vaccine show mixed results (Gerontology, 1995; 41: 3-10), and questions remain as to whether the inactivated virus used in the vaccine can truly provide complete protection (Int Arch Allergy Immunol, 1995; 108: 318-20).

Then there are the side-effects. While authorities say these are rare, this is cold comfort if you are among those affected. The ill-fated swine flu vaccine resulted in a rise of Guillain-Barré syndrome, a type of paralysis (Am J Epidemiol, 1979; 110: 105-23). In one UK study, around one in 12 patients said the flu vaccine was a trigger for asthma attacks (Lancet, 1998; 351: 326-31). Optic neuritis and permanent blindness, vasculitis and joint problems, reversible paralysis and myelopathy have also been reported (Am J Ophthalmol, 1997; 124: 703-4; J Rheumatol, 1997; 24: 1198-202; Ned Tijd Geneeskunde, 1995; 139: 2152-4; Muscle Nerve, 1995; 18: 1199-201).

Reviews of the benefits of vaccines in healthy adults have shown that these are negligible, sucessfully reducing the number of virus carriers (as shown by blood tests), but not of those who actually develop the flu (Cochrane Database Syst Rev, 2000; [2]: CD001269; Vaccine, 2000; 18: 957-1030).

Vitamin C, zinc and Echinacea Research shows that most of us treat colds and flu at home (J Fam Pract, 1998; 47: 366-9). Decades of research have gone into vitamin supplementation and immunity, and many nutrients have proved to be important in shoring up our immune defences (see box below).

The most popular of these are vitamin C and zinc, although opinion varies regarding their true effectiveness. In the 1970s, Linus Pauling’s review of the evidence concluded that large doses of vitamin C prevented colds and alleviated symptoms (Proc Natl Acad Sci USA, 1971; 68: 2678-81).

Since that time, however, the efficacy of vitamin C has been hotly debated. A 1975 analysis by Thomas Chalmers concluded that the case for vitamin C had “questionable validity” (Am J Med, 1975; 58: 532-6), but a recent analysis of the report suggests that his analysis was seriously flawed (J Am Coll Nutr, 1995; 14; 116-23).

It is now generally accepted that a dose of 1-8 g of vitamin C daily can decrease the severity of cold symptoms by an average of 23 per cent and reduce the duration of illness by nearly half (Scand J Infect Dis, 1994; 26: 1-6; Br J Nutr, 1992; 67: 3-16).

More recent reviews of the evidence say that, while vitamin C can alleviate cold symptoms, taking large doses is not preventative (Cochrane Database Syst Rev, 2000; [2]: CD000980). However, some groups may benefit from regular supplementation, such as athletes under heavy physical stress (Int J Sport Med, 1996; 17: 379-83). One review suggests a reduction in cold incidence of up to 50 per cent with regular vitamin C use (Int J Tuberc Lung Dis, 1999; 3: 756-61).

Zinc has long been promoted as a remedy and preventative for colds and flu. In one study, a nasal gel containing zinc significantly shortened the duration of a cold if taken within 24 hours of the onset of symptoms (Ear Nose Throat J, 2000; 79: 778-80, 782).