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Immunization Science

Safety of the Intranasal Influenza Vaccine

The article

Safety of cold-adapted live attenuated influenza vaccine in a large cohort of children and adolescents. Bergen R, Black S, Shinefield H, Lewis E, Ray P, Hansen J, Walker R, Hessel C, Cordova J, and Mendelman P. The Pediatric Infectious Disease Journal 2004;23(2):138-144

The question

How safe is the intranasal influenza vaccine (FluMist) in children and adolescents?

The study

This study evaluated the safety of the cold-adapted trivalent intranasal influenza virus vaccine (CAIV) containing two influenza A strains and one influenza B strain in healthy children and adolescents 1 through 17 years of age. Children whose parents recalled that they had ever had asthma/reactive airway disease were excluded.

Researchers enrolled 9,689 children in the study. Of these, 3,769 children 1 to 8 years of age received CAIV and 1,868 received placebo, whereas in children 9 to 18 years of age, 2,704 children received CAIV and 1,348 received placebo.

The researchers then followed the children for 42 days after each vaccination for any medically attended event or serious adverse event (SAE).

The findings

Researchers found that among all subjects the vaccine was not associated with conditions and infections often thought related to wild-type influenza, such as acute respiratory tract events, systemic bacterial infection, or acute gastrointestinal tract events.

The study also found that the vaccine was unlikely to be associated with other biologically plausible conditions, such as acute gastrointestinal events, acute respiratory events and abdominal pain.

However, it did find about a 4-fold increased risk of asthma in young children 18 to 35 months of age after receipt of CAIV. Some pf these infants had had asthma previously. There was no temporal relation of the onset of the wheezing with the administration of the vaccine. Wheezing episodes were equally distributed throughout the 42 day follow-up period.

The relevance/bottom line

FluMist was generally safe in older children and adolescents. However, there may be an increased risk of asthma in children younger than 36 months of age.

NNii’s comments

A surprising finding in this study was that some families did not recall that their child had been seen by a physician previously for asthma.