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Vaccines for preventing influenza in healthy children
Tom Jefferson1, Alessandro Rivetti2, Anthony Harnden3, Carlo Di
Pietrantonj2, Vittorio
Demicheli4
1
Vaccines Field, The Cochrane Collaboration, Roma, Italy.2
Servizio Regionale diRiferimento per l'Epidemiologia,
SSEpi-SeREMI - Cochrane Vaccines Field, Azienda
Sanitaria Locale ASL AL, Alessandria, Italy. 3Department of
Primary Health Care, Institute
of Health Sciences, Oxford, UK. 4Health Councillorship -
Servizio Regionale di Riferimento
per l'Epidemiologia, SSEpi-SeREMI - Cochrane Vaccines Field,
Regione Piemonte -
Azienda Sanitaria Locale ASL AL, Torino, Italy
Contact address: Tom Jefferson, Vaccines Field, The Cochrane
Collaboration, Via Adige
28a, Anguillara Sabazia, Roma, 00061,
[email protected]@assr.it;
[email protected].(Editorial group:Cochrane Acute
Respiratory Infections Group.)
Cochrane Database of Systematic Reviews, Issue 4, 2008 (Status
in this issue: Unchanged)Copyright 2008 The Cochrane Collaboration.
Published by John Wiley & Sons, Ltd.
DOI: 10.1002/14651858.CD004879.pub3
This version first published online: 23 April 2008 in Issue 2,
2008. Last assessed as up-to-
date: 29 September 2007
This record should be cited as: Jefferson T, Rivetti A, Harnden
A, Di Pietrantonj C,
Demicheli V. Vaccines for preventing influenza in healthy
children. Cochrane Database of
Systematic Reviews2008, Issue 2. Art. No.: CD004879. DOI:
10.1002/14651858.CD004879.pub3.
Abstract
Background
The consequences of influenza in children and adults are mainly
absenteeism from school
and work. However, the risk of complications is greatest in
children and people over 65 years
old.
Objectives
To appraise all comparative studies evaluating the effects of
influenza vaccines in healthy
children; assess vaccine efficacy (prevention of confirmed
influenza) and effectiveness
(prevention of influenza-like illness) and document adverse
events associated with influenzavaccines.
Search strategy
We searched the Cochrane Central Register of Controlled Trials
(CENTRAL) (The Cochrane
Library2007, issue 3); OLD MEDLINE (1950 to 1965); MEDLINE (1966
to September
2007); EMBASE (1974 to September 2007); Biological Abstracts
(1969 to September 2007);
and Science Citation Index (1974 to September 2007).
Selection criteria
Randomised controlled trials (RCTs), cohort and case-control
studies of any influenza
vaccine in healthy children under 16 years of age.
mailto:[email protected]:[email protected]:[email protected]:[email protected];%[email protected]:[email protected];%[email protected]:[email protected];%[email protected]:[email protected];%[email protected]://www.mrw.interscience.wiley.com/cochrane/clabout/articles/ARI/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/ARI/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/ARI/frame.htmlhttp://www.mrw.interscience.wiley.com/cochrane/clabout/articles/ARI/frame.htmlmailto:[email protected];%[email protected]:[email protected];%[email protected]:[email protected]
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Data collection and analysis
Two review authors independently assessed trial quality and
extracted data.
Main results
Fifty-one studies with 294,159 observations were included.
Sixteen RCTs and 18 cohort
studies were included in the analysis of vaccine efficacy and
effectiveness. From RCTs, livevaccines showed an efficacy of 82%
(95% confidence interval (CI) 71% to 89%) and an
effectiveness of 33% (95% CI 28% to 38%) in children older than
two compared with
placebo or no intervention. Inactivated vaccines had a lower
efficacy of 59% (95% CI 41% to
71%) than live vaccines but similar effectiveness: 36% (95% CI
24% to 46%). In children
under two, the efficacy of inactivated vaccine was similar to
placebo. Variability in study
design and presentation of data was such that a meta-analysis of
safety outcome data was not
feasible. Extensive evidence of reporting bias of safety
outcomes from trials of live
attenuated vaccines impeded meaningful analysis.
Authors' conclusions
Influenza vaccines are efficacious in children older than two
but little evidence is availablefor children under two. There was a
marked difference between vaccine efficacy and
effectiveness. No safety comparisons could be carried out,
emphasizing 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.
Plain language summary
Vaccines for preventing influenza in healthy children
Children and the elderly are the two age groups that appear to
have the most complications
following an influenza infection. Influenza has a viral origin
and often results in an acute
respiratory illness affecting the lower or upper parts
respiratory tract, or both. Viruses are
mainly of two subtypes (A or B) and spread periodically during
the autumn-winter months.
Many other viruses however, can also cause illness of the
respiratory tract.
Diffusion and severity of the disease could be very different
during different epidemics.
Efforts to contain epidemic diffusion rely mainly on widespread
vaccination. Recent policy
from several internationally-recognised institutions, recommend
immunisation of healthy
children between 6 and 23 month of age (together with their
contacts) as a public health
measure.
The review authors found that in children aged from two years,
nasal spray vaccines made
from weakened influenza viruses were better at preventing
illness caused by the influenza
virus (82% of illnesses were prevented) than injected vaccines
made from the killed virus
(59%). Neither type was particularly good at preventing
'flu-like illness' caused by other
types of viruses (33% and 36% respectively). In children under
the age of two, the efficacy of
inactivated vaccine was similar to placebo. It was not possible
to analyse the safety of
vaccines from the studies due to the lack of standardisation in
the information given but very
little information was found on the safety of inactivated
vaccines, the most commonly usedvaccine, in young children.
