Prior-Season Vaccination Not Associated With Flu Shot Effectiveness

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The researchers found that VE against influenza A(H3N2) was higher among children vaccinated in both the enrollment season and one prior season than among those without one prior-season vaccination.
The researchers found that VE against influenza A(H3N2) was higher among children vaccinated in both the enrollment season and one prior season than among those without one prior-season vaccination.

HealthDay News — Prior-season vaccination is not associated with reduced vaccine effectiveness (VE) among children aged 2 to 17 years, according to a study published online Oct. 26 in JAMA Network Open.

Huong Q. McLean, PhD, MPH, from Marshfield Clinic Research Institute in Wisconsin, and colleagues conducted a multiseason, test-negative case-control study involving children aged 2 to 17 years with a medically attended febrile acute respiratory illness. Children with influenza confirmed by reverse-transcription polymerase chain reaction were cases (772), while controls were children with negative test results for influenza.

Overall, 50% of the 3369 children included in the analysis had been vaccinated in the enrollment season. The researchers found that VE against influenza A(H3N2) was higher among children vaccinated in both the enrollment season and one prior season than among those without one prior-season vaccination (50.3% vs −82.4%, respectively; interaction P <.001) among recipients of the live attenuated influenza vaccine (LAIV). There was no correlation for LAIV effectiveness against influenza A(H1N1)pdm09 with prior-season vaccination (47.5% vs 7.8%; interaction P =.37). Prior-season vaccination was not associated with inactivated influenza vaccine effectiveness against influenza A(H3N2) (38.7% vs 23.2%; interaction P =.16) or influenza A(H1N1)pdm09 (72.4%  and 67.5%; interaction P =.93). For influenza B, residual protection from prior-season vaccination only (no vaccination in the enrollment season) was observed.

"These findings support current recommendations for annual influenza vaccination of children," the authors write.

Several authors disclosed ties to MedImmune/AstraZeneca.

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