Mechanism for Seasonal Vaccine Effect on Pandemic H1N1 Risk Remains Uncertain

Open Access
Publisher Website
Google Scholar
Abstract
TO THE EDITOR—After correcting for possible cross-reactions, Cowling et al [1] report significantly higher rates of pandemic H1N1 (pH1N1) infection among children 6–15 years old randomized to receive trivalent inactivated influenza vaccine (TIV) versus placebo (31% vs. 12%; P = .04). As a randomized-controlled trial, their crude estimate of the risk ratio (RR = 2.58) among randomized participants is conceptually the most valid. Surprisingly, that primary finding is conveyed in neither their manuscript title nor in the commentary by Glezen [1, 2]. Cowling et al instead draw inconsistent conclusions by combining the 119 randomized children with 312 nonrandomized household contacts (Table 6 [1]). This approach seems inappropriate given that 77% of household contacts were >15 years old (Table 1 [1])—an age group not included in randomized subjects and in whom the pH1N1 attack rate was lower (Table 7 [1])—thereby diluting findings in the randomized children with noncomparable and mostly (90%) nonvaccinated adults (Table 1 [1]).