Giving inactivated influenza vaccine to young children is effective at preventing influenza, even in infants younger than 2 years who are the most vulnerable to infection, according to an Article published Online First in The Lancet Infectious Diseases . These findings suggest that the influenza immunisation recommendations of most countries should be re-examined.
Children under 2 years old experience higher rates of illness from influenza than any other age group except the over 65s, and have a tendency to spread infection to other family members and the community.
Previous research has suggested that yearly immunisation of young children against influenza is cost-effective. However, few studies have been done to determine the effectiveness of the vaccine in children younger than 2 years, which has resulted in a widespread belief that influenza vaccines are not effective in this age group. This lack of evidence has convinced few countries to recommend universal vaccination in young children. Indeed, Finland is the only country in Europe that recommends universal immunisation of children aged 6 to 35 months.
To provide more evidence, Terho Heikkinen from Turku University Hospital, Finland, and Finnish colleagues evaluated the effectiveness of trivalent (ie, containing antigens to give immunity against two strains of influenza A virus and one of influenza B) inactivated influenza vaccine during the influenza season 2007 in Finland. The researchers calculated the effectiveness of the vaccine by comparing the number of laboratory-confirmed influenza A and B infections in 631 prospectively followed children aged 9 to 40 months old who did and did not receive the vaccine.
Overall, the effectiveness of vaccination was 66% against any influenza, and 84% against influenza A viruses.
In children younger than 2 years overall effectiveness of vaccination was 66%, and 79% against influenza A strains.
The authors note that although the vaccine had good effectiveness against well-matched A strains, almost half of all cases (33 of 71) of influenza were caused by mismatched influenza B viruses, against which the vaccine was not effective.
They say: "Our findings accord with recent studies showing a clear correlation between the effectiveness of the vaccine and the match between the vaccine and circulating strains…[suggesting] that the clinical effectiveness of influenza vaccination is far more dependent on the match of the vaccine antigens than the age of the recipient."
The authors were unable to record any adverse events associated with the vaccination of children in the study. However, national safety data suggest the dose was well tolerated, with only 38 adverse events (most commonly fever or eczema) reported for 63 048 children aged 6 to 35 months who had at least one dose of the vaccine.
They conclude: "These results provide clear evidence for effectiveness of the inactivated influenza vaccine even in the youngest children during seasons with normal influenza activity and a good antigenic match between the vaccine and the circulating strains of influenza…Our findings suggest that influenza vaccine recommendations should be reassessed in most countries."
In a Comment, Mark Steinhoff from Cincinnati Children's Hospital Medical Center, Cincinnati, USA, says that these findings highlight the need for European centres to conduct a large, multicentre, multiyear randomised trial of influenza immunisation of young infants, "to assess the cost-effectiveness of a strategy for universal immunisation for influenza in children and the broader effect for such a strategy on families and communities."
Dr Terho Heikkinen, Turku University Hospital, Turku, Finland. T) +358 50 5359095 E) terho.heikkinen@utu.fi
Dr Mark Steinhoff, Cincinnati Children's Hospital Medical Center, Cincinnati, USA. T) +1 513 636 1376 E) m.steinhoff@gmail.com or mark.steinhoff@cchmc.org
For full Article and Comment, see: http://press.thelancet.com/tlidfluinfant.pdf
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The Lancet Infectious Diseases