1. Synthesis of results and conclusions from the previous versions of the present review.
| Review version (searches date) | Number of included trials (RCT/CCT) | Number of included observational studies | Estimates of effect (RCTs/CCTs only) | Conclusions from the Abstract |
| Version 1 (15 November 2005) |
38 | 13 (12 cohorts and 1 case‐control study) |
Influenza‐like illness LAIV = 33% (95% CI 28% to 38%) TIV = 36% (95% CI 24% to 46%) Influenza LAIV = 79% (95% CI 48% to 92%) TIV = 59% (95% CI 41% to 71%) |
Influenza vaccines are efficacious in children older than two years, but little evidence is available for children under two. There was a marked difference between vaccine efficacy and effectiveness. That no safety comparisons could be carried out emphasises the need for standardisation of methods and presentation of vaccine safety data in future studies. It was surprising to find only one study of inactivated vaccine in children under two years, given recent recommendations to vaccinate healthy children from six months old in the USA and Canada. If immunisation in children is to be recommended as public health policy, large‐scale studies assessing important outcomes and directly comparing vaccine types are urgently required. |
| Version 2 (20 February 2008) |
40 | 21 (18 cohorts and 3 case‐control studies) |
Influenza‐like illness LAIV = 33% (95% CI 28% to 38%) TIV = 36% (95% CI 24% to 46%) Influenza LAIV = 82% (95% CI 71% to 89%) TIV = 59% (95% CI 41% to 71%) |
Influenza vaccines are efficacious in children older than two, but little evidence is available for children under two. There was a marked difference between vaccine efficacy and effectiveness. No safety comparisons could be carried out, emphasising the need for standardisation of methods and presentation of vaccine safety data in future studies. It was surprising to find only one study of inactivated vaccine in children under two years, given current recommendations to vaccinate healthy children from six months old in the USA and Canada. If immunisation in children is to be recommended as a public health policy, large‐scale studies assessing important outcomes and directly comparing vaccine types are urgently required. |
| Version 3 (9 July 2012) |
43 | 33 (21 cohorts and 12 case‐control studies) |
Influenza‐like illness LAIV = 33% (95% CI 28% to 38%) TIV = 36% (95% CI 24% to 46%) Influenza LAIV = 80% (95% CI 68% to 87%) TIV = 59% (95% CI 41% to 71%) |
Influenza vaccines are efficacious in preventing cases of influenza in children older than two years of age, but little evidence is available for children younger than two years of age. There was a difference between vaccine efficacy and effectiveness, partly due to differing data sets, settings, and viral circulation patterns. No safety comparisons could be carried out, emphasising the need for standardisation of methods and presentation of vaccine safety data in future studies. In specific cases, influenza vaccines were associated with serious harms such as narcolepsy and febrile convulsions. It was surprising to find only one study of inactivated vaccine in children under two years, given current recommendations to vaccinate healthy children from six months of age in the USA, Canada, parts of Europe, and Australia. If immunisation in children is to be recommended as a public health policy, large‐scale studies assessing important outcomes and directly comparing vaccine types are urgently required. The degree of scrutiny needed to identify all global cases of potential harms is beyond the resources of this review. |
CCT: comparative controlled trial LAIV: live attenuated influenza vaccine RCT: randomised controlled trial TIV: trivalent inactivated influenza vaccine