USA and Canada’s influenza vaccination programmes for children based on little evidence

25 February 2005

Children in the USA and Canada are being vaccinated against influenza without adequate proof that it will work, concludes a study by researchers in Oxford and Italy published in this week’s issue of The Lancet.

Most immunisation campaigns target people aged 65 years or older. However, the USA and Canada have recently started vaccinating children, including those aged 6–24 months.

In their review of the evidence, the researchers found that there are no published trials supporting the view that vaccination offers protection against influenza to healthy children under two years old. ‘We just cannot understand how you can vaccinate millions of small children in the absence of convincing scientific evidence that the vaccines make any difference,’ commented Dr Tom Jefferson of Cochrane Vaccines Field, Italy, lead author of the review.

The aim of the USA and Canada in vaccinating children is to reduce disease spread; admissions and visits to hospitals; deaths of elderly relatives; complications (such as ear infections and pneumonia); absences from school; parental loss of workdays; and over-prescribing of antibiotics. However, there is no evidence that vaccinating children can achieve these goals.

Although there is a growing body of evidence showing the impact of influenza on hospitalisations and deaths of children, at present there is no convincing data to suggest that vaccines can reduce mortality, hospital admissions, serious complications and community transmission of influenza. There was some evidence suggesting vaccines can reduce school absences.

Sue Smith and Anthony Harnden in the Department of Primary Health Care in Oxford and colleagues in Italy identified and assessed 25 comparative studies that evaluated the efficacy (reduction in laboratory-confirmed cases) 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 two years or older, especially for two-dose live attenuated vaccines. However, we noted a striking difference between efficacy and effectiveness of vaccines, because of the large proportion of influenza-like illness caused by agents other than influenza viruses. This is an important point in the decision to immunise whole populations.

‘Immunisation of very young children is not lent support by our findings. Although a growing body of evidence shows effect of influenza on admissions and deaths of children, we recorded no convincing evidence that vaccines can reduce mortality, hospital admissions, serious complications and community transmission of influenza.’

Contact: Dr Tom Jefferson, Cochrane Vaccines Field, Via Adige 28a 00061 Anguillara Sabazia, Roma, Italy. T) +39 06 999 00 989 (mo +39 32 92025051) toj1@aol.com

Notes to Editors

• ‘Assessment of the efficacy and effectiveness of influenza vaccines in healthy children: systematic review’, by T Jefferson, S Smith, V Demicheli, A Harnden, A Rivetti, Jefferson T, Smith S, Demicheli V, Harnden A, Rivetti A, and C Di Pietrantonjappears in The Lancet on 25 February 2005.