Absolute and Relative Effectiveness of Cell Culture–Based and Egg–Based Quadrivalent Inactivated Influenza (Flu) Vaccine Products From the 2014–2015 to 2018–2019 Seasons, US Flu VE Network

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BACKGROUND: Estimates of the annual effectiveness of influenza vaccination combine multiple vaccine types. Reports of brand/product-specific vaccine effectiveness (VE) of egg-based and cell culture-based quadrivalent inactivated influenza vaccines (IIV4 and ccIIV4, respectively) are limited. METHODS: Using an observational test-negative study design, we compared the effectiveness of selected IIV4 and ccIIV4 products among outpatients enrolled in the US Influenza Vaccine Effectiveness (Flu VE) Network from 2014-2015 to 2018-2019. We used multivariable logistic regression to estimate the product-specific and age group-specific absolute VE and relative VE (rVE) of recommended, age-appropriate vaccines against symptomatic laboratory-confirmed outpatient influenza. The rVE of ccIIV4 versus IIV4 products was estimated during 2 seasons from 2017-2019 among participants aged ≥4 years. RESULTS: Pooling data from 5 influenza seasons when 18% and 15% of vaccinated patients had received Fluarix Quadrivalent or Fluzone Quadrivalent IIV4, respectively, the VE against influenza was 32% for Fluarix and 37% for Fluzone. Pooling 2 seasons when 11% and 28% of vaccinated patients had received ccIIV4 (Flucelvax Quadrivalent) and IIV4 (FluLaval Quadrivalent), respectively, the VE against influenza for each product was 30%. The absolute VE compared with unvaccinated patients was lowest against influenza A(H3N2) compared with that against A(H1N1)pdm09 and each B lineage; VE point estimates were lowest among patients aged ≥50 years compared with 2 younger age groups. The rVE estimates were not statistically significant, indicating similar protection across vaccine products. CONCLUSIONS: Comparisons of influenza vaccine products over multiple seasons showed benefit of both IIV4 and ccIIV4 against symptomatic laboratory-confirmed outpatient influenza, with similar absolute and relative levels of protection provided by each product.

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