Factors Associated with Influenza A (H1N1)pdm09 (pH1N1) Vaccine Failure among Children Aged 5-17 Years
Methods: We recruited children who were enrolled in a study of influenza vaccine effectiveness during the prior 2012-13 season; all had medically attended acute respiratory illness, were tested for influenza, and had known vaccination history. Participants received one dose of 2013-14 vaccine, either inactivated influenza vaccine (IIV3) or quadrivalent live attenuated influenza vaccine (LAIV4), based on preference. Hemagglutination-inhibition (HI) titers against pH1N1 were measured pre- and 21 days post-vaccination. Seroprotection was defined as HI titer ≥1:40. Children <9 years were classified as partially vaccinated if they had received no prior dose of a vaccine containing pH1N1. Active surveillance was performed for acute respiratory illness; nasal and throat swabs from ill children were tested by RT-PCR. Cases were children with pH1N1 infection (vaccine failures); all other children served as controls. Logistic regression was used to assess factors associated with vaccine failure.
Results: During 2013-14, among 162 vaccinated children, 11 (7%) were pH1N1 cases. Eight (73%) cases and 54 (36%) controls had received 2013-14 LAIV4 (p=0.02). Postvaccination HI titers against pH1N1 were <1:40 in 10 (91%) cases and 34 (23%) controls (p<0.001). Compared to children 9-17 years, risk of vaccine failure was higher in children 5-8 years with no prior pH1N1 vaccination (OR 74; 95% CI 7.7, 720), and in children 5-8 years with ≥1 prior pH1N1 vaccinations (OR 5.9; 95% CI 1.2, 31). There were no differences between vaccine failures and controls by sex, high risk condition, history of influenza infection in 2012-13, or age at first influenza vaccination.
Conclusion: Vaccine failure in children was associated with receipt of LAIV4, low postvaccination HI titer, and younger age. The risk was highest among children 5-8 years old who had not been previously vaccinated. Larger studies in children are needed to better understand risk of vaccine failure.
MedImmune: Collaborator, Research grant
M. Sundaram, MedImmune, LLC: Project scientist on MedImmune-funded grant, Research grant
J. Meece, None
S. Spencer, None
J. H. Kim, None
T. Friedrich, None
B. Flannery, None
A. M. Fry, None
E. Belongia, Medimmune LLC: Grant Investigator, Grant recipient