No clinically meaningful safety signals were observed in association with the administration of the quadrivalent live attenuated influenza vaccine (Q/LAIV), according to results of a large population study published in Vaccine.

In a prospective, nonrandomized, observational cohort study ( identifier: NCT01985997), data from the Kaiser Permanente Northern California (KPNC) health plan were analyzed from 62,040 Q/LAIV (FluMist®, MedImmune, Gaithersburg, MD) recipients aged 2 to 49 years during the 2013 to 2014 influenza season.

Roger Baxter, MD, co-director of the Kaiser Permanente Vaccine Study Center in Oakland, California, and colleagues compared rates of medically attended events and hospitalization immediately after Q/LAIV vaccination with rates observed during the reference periods later in the follow-up period (within-cohort analysis).  Rates were also compared with 2 frequency-matched groups: inactivated influenza vaccine (IIV) recipients and unvaccinated controls.

Of the 62,040 Q/LAIV recipients, 88% (n=54,647) were aged 2 to 17 years, including 29,992 children between the ages of 2 and 8 years. Within 42 days following vaccination, lower respiratory tract infections (n=157) and wheezing (n=121) were the most frequent incident events in Q/LAIV recipients. During this period, 41 Q/LAIV recipients were hospitalized, 3 of which were hospitalized for respiratory disease. During the risk interval (days 0 to 3), 14 Q/LAIV recipients were diagnosed with hypersensitivity; seizures and convulsions were not observed during this time.

When compared by age group, Q/LAIV recipients aged 5 to 8 years had a significantly higher risk of hypersensitivity during the risk interval (days 0 to 3) vs the reference period (days 7 to 9; 5 vs 0 cases, P =.05); however, no one was seen in an emergency department or admitted to a hospital. This observation was limited to children attending/visiting physician clinics.

Compared with unvaccinated controls by age group (n=44), Q/LAIV recipients 2 to 4 years of age (n=66) were at higher risk of wheezing (adjusted hazard ratio [HR] 1.50; 95% CI, 1.03-2.20). Within this group, 4 Q/LAIV recipients and 5 unvaccinated controls required treatment in the emergency department; none were hospitalized. Again, this observation was limited to children attending/visiting physician clinics.

No significant risk was observed between Q/LAIV and IIV recipients in any setting, including analyses by age group. However, a complementary analysis conducted among children between the ages of 2 and 4 years with a history of wheezing or asthma showed that the risk of wheezing after vaccine administration was lower among Q/LAIV recipients (HR 0.21; 95% CI, 0.01-1.22) than among IIV recipients (HR 0.51; 95% CI, 0.02-4.79).

No safety signals were observed with the administration of Q/LAIV. “These results are consistent with those of other pre-approval and post-licensure clinical studies that have demonstrated the safety of Q/LAIV among eligible children, adolescents, and adults,” concluded the researchers.


Co-authors Herve Caspard and Christopher S. Ambrose are full-time employees of AstraZeneca. This study was sponsored by MedImmune, the global biologics research and development arm of AstraZeneca. MedImmune/AstraZeneca participated in the study design, review, and interpretation of study data, and development of the manuscript.

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Baxter R, Eaton A, Hansen J, Aukes L, Caspard H, Ambrose CS. Safety of quadrivalent live attenuated influenza vaccine in subjects aged 2-49 years. Vaccine. 2017;35:1254-1258. doi: 10.1016/j.vaccine.2017.01.062