Most immunisation campaigns target people aged 65 years or older. The USA and Canada have recently started vaccinating children, including those aged 6 to 24 months, in the hope of reducing disease spread, admissions and visits to hospitals, deaths of elderly relatives, complications (such as ear infections and pneumonia), absences from school, and parental loss of workdays and over-prescribing of antibiotics. However, there is no evidence that vaccinating children can achieve these goals.

Tom Jefferson (Cochrane Vaccines Field, Italy) and colleagues identified and assessed 25 comparative studies that evaluated the efficacy (reduction in laboratory confirmed case) and effectiveness (reduction in symptomatic cases) on influenza vaccines in healthy children aged 16 years or younger.

Vaccines of live viruses with weakened infectivity had 79% efficacy and 38% effectiveness in children older than two years compared with placebo or no immunisation. Inactivated vaccines had a lower efficacy (65%) than live weakened vaccines, and in children aged two years or younger they had similar effects to placebo. Effectiveness of inactivated vaccines was about 28% in children older than two years. Vaccines were effective in reducing long school absences but had little effect on other outcomes such as hospital stays and lower respiratory tract disease, when compared with placebo or no intervention. However, the authors note that these conclusions are based on a small number of studies.

Dr Jefferson concludes: "We have identified a large dataset showing reasonable quality evidence of efficacy of influenza vaccines in children age 2 years or older, especially for two-dose live attenuated vaccines. However, we noted a striking difference between efficacy and effectiveness of vaccin
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Lancet
24-Feb-2005