Effect of Influenza Vaccination of Children on Infection Rate in Hutterite Communities: Follow-Up Study of a Randomized Trial

<div><p>Background</p><p>An earlier cluster randomized controlled trial (RCT) of Hutterite colonies had shown that if more than 80% of children and adolescents were immunized with influenza vaccine there was a statistically significant reduction in laboratory-confirmed influenza among all unimmunized community members. We assessed the impact of this intervention for two additional influenza seasonal periods.</p><p>Methods</p><p>Follow-up data for two influenza seasonal periods of a cluster randomized trial involving 1053 Canadian children and adolescents aged 36 months to 15 years in Season 2 and 1014 in Season 3 who received the study vaccine, and 2805 community members in Season 2 and 2840 in Season 3 who did not receive the study vaccine. Follow-up for Season 2 began November 18, 2009 and ended April 25, 2010 while Season 3 extended from December 6, 2010 and ended May 27, 2011. Children were randomly assigned in a blinded manner according to community membership to receive either inactivated trivalent influenza vaccine or hepatitis A. The primary outcome was confirmed influenza A and B infection using RT-PCR assay. Due to the outbreak of 2009 H1N1 pandemic, data in Season 2 were excluded for analysis.</p><p>Results</p><p>For an analysis of the combined Season 1 and Season 3 data, among non-recipients (i.e., participants who did not receive study vaccines), 66 of the 2794 (2.4%) participants in the influenza vaccine colonies and 121 of the 2301 (5.3%) participants in the hepatitis A colonies had influenza confirmed by RT-PCR, for a protective effectiveness of 60% (95% CI, 6% to 83%; P = 0.04); among all study participants (i.e., including both those who received study vaccine and those who did not), 125 of the 3806 (3.3%) in the influenza vaccine colonies and 239 of the 3243 (7.4%) in the hepatitis A colonies had influenza confirmed by RT-PCR, for a protective effectiveness of 63% (95% CI, 5% to 85%; P = 0.04).</p><p>Conclusion</p><p>Immunizing children and adolescents with inactivated influenza vaccine can offer a protective effect among unimmunized community members for influenza A and B together when considered over multiple years of seasonal influenza.</p><p>Trial Registration</p><p>Clinicaltrials.gov <a href="https://clinicaltrials.gov/ct2/show/NCT00877396?term=NCT00877396&rank=1" target="_blank">NCT00877396</a></p></div

Participant flow.

<p>Participant flow.</p

Protective Effectiveness of Immunizing Children and Adolescents With Influenza Vaccine on All Participants.

<p>Protective Effectiveness of Immunizing Children and Adolescents With Influenza Vaccine on All Participants.</p

Association of secondary outcomes in all participants ^a.

<p>Association of secondary outcomes in all participants <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167281#t005fn001" target="_blank">^a</a>.</p

Influenza A or B Detected in All Participants in the Study ^a.

<p>Influenza A or B Detected in All Participants in the Study <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167281#t002fn001" target="_blank">^a</a>.</p

Baseline Characteristics of All Study Participants in 65 Colonies (32 in Influenza Vaccinated Group and 33 in Hepatitis A Vaccinated group) at First Entry to Study.

<p>Baseline Characteristics of All Study Participants in 65 Colonies (32 in Influenza Vaccinated Group and 33 in Hepatitis A Vaccinated group) at First Entry to Study.</p

Protective Effectiveness on Nonrecipients of Immunizing Children and Adolescents With Influenza Vaccine.

<p>Protective Effectiveness on Nonrecipients of Immunizing Children and Adolescents With Influenza Vaccine.</p