The Influenza-Associated Hospitalization Surveillance Network (FluSurv-NET) has been previously described.[5,7] Briefly, FluSurv-NET conducts all-age, population-based surveillance for laboratory-confirmed influenza-associated hospitalizations in selected states representing approximately 8%–9% of the U.S. population. Persons met the FluSurv-NET case definition if they resided in the FluSurv-NET catchment area,* were admitted to a hospital during October 1–April 30† and received a positive influenza test result ≤14 days before hospitalization or during hospitalization. Cases in persons aged <18 years and cases from the 2020–21 season were excluded from this analysis because case counts during this season were too low to calculate rates by race and ethnicity.
Population denominators used for rate estimation were obtained from the National Center for Health Statistics.§ Unadjusted rates, stratified by age group (18–49, 50–64, 65–74, and ≥75 years), race and ethnicity,¶ and influenza season were calculated by dividing the number of hospitalizations by the total catchment population. Unadjusted rates by race, ethnicity, and age group were multiplied by the age distribution of the total FluSurv-NET catchment population to obtain age-adjusted rates; the age groups referenced previously were used for the age adjustment. For rates and rate ratios (RRs), 95% CIs were calculated assuming a simple random sample design and a normal distribution via the SAS STDRATE procedure. All analyses were conducted using SAS software (version 9.4; SAS Institute).
Influenza Vaccination Coverage
The Behavioral Risk Factor Surveillance System (BRFSS) is a state-based random-digit–dialed cellular and landline telephone survey that collects information on various health conditions and risk behaviors from one randomly selected adult aged ≥18 years in a household.** BRFSS data for adults aged ≥18 years were analyzed to estimate influenza vaccination coverage for the 2010–11 through 2021–22 influenza seasons. The analysis includes data collected from interviews completed during September–June of each season and vaccine doses received during July–May. Respondents were asked if they had received an influenza vaccine in the past 12 months, and if so, in which month and year. Vaccination coverage estimates were calculated using Kaplan-Meier survival analysis, as previously described. For the 2021–22 season, for which more detailed data stratified by race and ethnicity and access to care variables are presented, vaccination coverage estimates are based on 291,839 completed interviews; 28,007 respondents were excluded from the analysis because there was no information on whether they had received an influenza vaccine in the past 12 months. The median state BRFSS response rate for a complete or partially complete interview was 42.5% for September–December 2021 and 45.4% for January–June 2022. All estimates were weighted and analyzed using SAS (version 9.4; SAS Institute) and SAS-callable SUDAAN (version 11.0.3; RTI International) statistical software to account for the complex survey design. Differences between estimates were determined using t-tests with p-values <0.05 considered statistically significant.
For each data system, activities were reviewed by CDC and were conducted consistent with applicable federal law and CDC policy.†† Sites participating in FluSurv-NET obtained approval from their respective state and local institutional review boards, as applicable. The requirement for informed consent was waived per 45 CFR 46.
Morbidity and Mortality Weekly Report. 2022;71(43):1366-1373. © 2022 Centers for Disease Control and Prevention (CDC)