Seasonal flu vaccine failed to prevent pandemic infection in children

Nelson CA. Pediatr Infect Dis J. 2011;doi:10.1097/INF.0b013e31820bb482.

The 2008-2009 seasonal flu vaccine neither prevented nor increased the risk for medically attended pandemic H1N1 infection in a cohort of children, according to a study.

Although the seasonal vaccine protected against H1N1 in some studies of adults, the same effectiveness has not been verified in pediatric populations. The seasonal vaccine was also suspected of increasing the risk for H1N1 infection by pre-empting influenza A induction of heterosubtypic immunity to antigenically distinct strains.

For the current study, the researchers recorded seasonal influenza vaccination status in 165 patients aged 18 months to 18 years with lab-confirmed pandemic H1N1 infection. A group of 660 age- and gender-matched Kaiser Permanente patients without H1N1 served as controls.

The researchers found that children with pandemic H1N1 infection were neither more nor less likely to have received the seasonal flu vaccine (OR=1.31; 95% CI, 0.92-1.88). Children with H1N1 were more likely to have an underlying chronic health condition than controls (45% vs. 21%, P<.0001). Still, after adjusting for these conditions and health-seeking behavior, H1N1 patients were just as likely as controls to have received the seasonal flu vaccine (OR=1.08; 95% CI, 0.75-1.57).

"An estimated 24% of all children in the United States received the seasonal influenza vaccine during the 2008-2009 season, many of whom will likely be exposed to further H1N1 waves and/or other pandemic influenza strains in the future," the researchers said. "Evidence that seasonal influenza vaccination neither increases nor decreases susceptibility to pandemic influenza has important implications for influenza vaccination guidelines, pandemic control and future influenza-related research."

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