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Effectiveness of Inactivated Influenza Vaccine

The article

Efficacy of inactivated and cold-adapted vaccines against influenza A infection, 1985 to 1990: the pediatric experience. Neuzil KM, Dupont WD, Wright PF, Edwards KM. The Pediatric Infectious Disease Journal 2001;20(8): 733-740 

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The question

How effective are the inactivated vaccines against Influenza A in children 1 to 16 years of age?

The study

Researchers at Vanderbilt University reanalyzed the data from a trial conducted from 1985 through 1990, of inactivated influenza vaccines for the prevention of influenza A disease. They were compared to a cold-adapted vaccine that was under development and a placebo (inactivated influenza B vaccine).

The investigators sought to determine vaccine safety, immunogenicity (immune response) and efficacy in patients younger than 16 years.

During the 5 years of the study 791 children younger than age 16 years received 1809 doses of either inactivated or cold-adapted vaccine or placebo. Each child received the same kind of vaccine each year. A total of 277 children received the inactivated vaccine. Inactivated vaccines contained the influenza types more common during the years of the study, H1N1 and H3N2.

Although two doses of influenza vaccine are recommended for children receiving vaccine for the first time, only one dose was given in this study. The children were followed for viral cultures positive to influenza illness.

The findings

Inactivated influenza vaccines reduced the occurrence of respiratory illness caused by influenza A type H1N1 viruses by 91.4% compared to persons who did not receive the vaccine. Illnesses caused by the type H3N2 viruses were reduced by 77.3%.

The vaccines were well-tolerated, and there were no serious reactions.

The relevance/bottom line

Inactivated trivalent influenza A vaccines are well-tolerated in children without serious reactions even when given yearly. They were effective in the prevention of culture-proven influenza A disease in children 1 to 16 years old. Although this study was conducted more than a decade ago, its results are still applicable.

NNii’s comment

Although small, this study showed that annual inactivated influenza vaccine seems to be both safe and effective in children.

The study had too few young infants 6 to 23 months of age (the age at which all children are recommended to receive trivalent influenza vaccine) to be able to evaluate either safety or efficacy in this age group.

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