Flu Vaccine Effective for Young Children, Despite Mismatch

New research has indicated that the inactivated quadrivalent influenza vaccine (IIV4) vaccine is effective against influenza A and B in children aged 6 to 35 months.

In a phase 3, multinational trial, Carine Claeys, MD, and colleagues evaluated 12,018 healthy children from 13 countries from October 1, 2011, to December 31, 2014. Each child was randomly assigned to receive either IIV4 (n = 6006), consisting of 15 μg haemagglutinin antigen per strain per 0.5 mL dose, or to 1 to 2 doses of a non-influenza control vaccine (n = 6012).
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Vaccine-primed participants in the IIV4 group received a single dose at baseline, while vaccine-unprimed participants received 2 doses at baseline and on day 28. For both groups, cultured isolates from nasal swabs were categorized as antigenically matched or mismatched to vaccine strains.

In addition, the researchers examined vaccine efficacy in the per-protocol group and total vaccinated group, as well as vaccine safety in the total vaccinated group.

Findings showed that at least 1 case of reverse transcription polymerase chain reaction-confirmed influenza had occurred in 356 (6%) children in the IIV4 group and 693 (12%) children in the control group.

Of these cases, 138 (13%) were A/H1N1 strains, 529 (50%) were A/H3N2 strains, 69 (7%) were B/Victoria strains, and 316 (30%) were B/Yamagata strains. A total of 539 (64%) of 848 antigenically characterized isolates were found to be vaccine-mismatched.

Ultimately, IIV4 was found to be 63% effective against moderate-to-severe influenza and 50% effective against all influenza in the per-protocol group, compared with 64% effective against moderate-to-severe influenza and 50% effective against all influenza in the total vaccinated group.

The researchers did not observe any clinically significant differences in safety between IIV4 and control vaccines.

“IIV4 prevented influenza A and B in children aged [6 to 35] months despite high levels of vaccine mismatch,” the researchers concluded. “Vaccine efficacy was highest against moderate-to-severe disease, which is the most clinically important endpoint associated with greatest burden.”

—Christina Vogt

Reference:

Claeys C, Zaman K, Dbaibo G, et al. Prevention of vaccine-matched and mismatched influenza in children aged 6–35 months: a multinational randomised trial across five influenza seasons [Published online March 5, 2018]. Lancet Child Adolescent Health. https://doi.org/10.1016/S2352-4642(18)30062-2.