Seasonal Influenza Vaccination Coverage — United States, 2009–10 and 2010–11

Anne F. McIntyre, PhD

Amparo G. Gonzalez-Feliciano, MPH

Leah N. Bryan, MPH,

Tammy A. Santibanez, PhD

Walter W. Williams, MD

James A. Singleton, PhD

National Center for Immunization and Respiratory Diseases, CDC

Corresponding author: Anne F. McIntyre, PhD, National Center for Immunization and Respiratory Diseases, CDC. Telephone: 404-639-8284; E-mail: AMcIntyre@cdc.gov.

Introduction

Infection with influenza viruses can cause severe morbidity and mortality among all age groups. Children, particularly those aged <5 years (1–3), have the highest incidence of infection during epidemic periods; however, the highest rates of influenza-associated hospitalizations and deaths are among the elderly (aged ≥65 years), children aged <2 years, and those of any age with underlying medical conditions (1,4,5). Each year, influenza-related complications are estimated to result in more than 226,000 hospitalizations (6). During 1976–2006, estimates of influenza-associated deaths in the United States ranged from approximately 3,000 to an estimated 49,000 persons (7,8) (http://www.cdc.gov/flu/keyfacts.htm#howserious). Annual vaccination is the most effective strategy for preventing influenza virus infection and its complications (9).

Racial and ethnic disparities in seasonal influenza vaccination coverage have been observed in previous influenza seasons among children and adults (10). This summary updates the evaluation of these disparities among all persons aged ≥6 months, previously reported for the 2000–01 through the 2009–10 season (10), with findings from the 2010–11 influenza season and compares coverage in 2009–10 and 2010–11. For the 2010–11 influenza season, the Advisory Committee on Immunization Practices (ACIP) expanded its recommendations to include annual influenza vaccination of all persons aged ≥6 months (11). For the first time, the 2010–11 ACIP flu season recommendations included healthy adults aged 18–49 years.

This report is part of the second CDC Health Disparities and Inequalities Report (CHDIR) (12). The 2011 CHDIR (13) was the first CDC report to assess disparities across a wide range of diseases, behavioral risk factors, environmental exposures, social determinants, and health-care access. The criteria for inclusion of topics that are presented in the 2013 CHDIR are described in the 2013 CHDIR Introduction (14). This report provides an update on the progress of influenza vaccination coverage in the United States, by age, race/ethnicity, and risk status. The purposes of this report on influenza vaccination are to discuss and raise awareness of differences in the characteristics of populations who received influenza vaccination, and to prompt actions to reduce disparities.

Methods

To estimate the progress of influenza vaccination coverage in the United States, by age, race/ethnicity, and risk status, various data sources were used. Age groups were defined as aged <45 years, 45–74 years, <75 years, ≥75 years, and ≥85 years. Race was defined as white, black, Asian/Pacific Islander (A/PI), American Indian/Alaska Native (AI/AN), and other and multiple race. Ethnicity was defined as Hispanic or non-Hispanic. Race/ethnicity categories are mutually exclusive. For the 2009–10 season, high risk conditions included asthma, other lung problems, diabetes, heart disease, kidney problems, anemia, and weakened immune system caused by a chronic illness or by medicines taken for a chronic illness. For the 2010–11 season, high risk conditions included asthma, diabetes, and heart disease. Other medical conditions that place persons at increased risk for complications from influenza (11) were not under surveillance for this report. For this update, vaccination by household income, educational attainment, poverty status, disability status, and geographic location were not analyzed. Data on place of birth was not available.

To estimate the proportion of persons aged ≥6 months who received influenza vaccination during the 2009–10 influenza season, combined data from the National 2009 H1N1 Flu Survey (NHFS) and the Behavioral Risk Factor Surveillance System (BRFSS) were used. The NHFS included children identified from the National Immunization Survey (NIS) and from a stand-alone telephone survey. To estimate the proportion of children aged 6 months through 17 years who received influenza vaccination during the 2010–11 influenza season, data from the NIS were used. To estimate the proportion of adults aged ≥18 years who received influenza vaccination during the 2010–11 influenza season, BRFSS data were used. Both NIS and BRFSS collected monthly data on vaccinations reported during August 2010 through May 2011 for all 50 states and the District of Columbia.

Comparisons between the 2010–11 and 2009–10 seasons used estimates for the recommended trivalent seasonal vaccines (11,15), and all 2009–10 estimates in this report are for trivalent seasonal vaccination, although for the 2009–10 seasons, two vaccines were recommended: the trivalent seasonal vaccine (15), along with the influenza A(H1N1)pdm09 monovalent vaccine to provide immunity against the pandemic strain that emerged in 2009 (16). Coverage estimates for all persons aged ≥6 months were determined using combined state-level monthly estimates weighted by the age-specific populations of each state. In 2009–10, the unweighted sample sizes for children aged 6 months through 17 years and persons ≥18 years were 149,872 and 361,485, respectively (http://www.cdc.gov/flu/professionals/vaccination/coverage_0910estimates.htm). For 2010–11, the unweighted sample size for children aged 6 months through 17 years was 116,799 and 377,569 for persons ≥18 years (http://www.cdc.gov/flu/professionals/vaccination/coverage_1011estimates.htm).

Disparities were measured as the deviations from a "referent" category cumulative proportion. Absolute difference was measured as the simple difference between a population subgroup estimate and the estimate for its respective reference group. A description of the methods for estimating national influenza vaccination coverage and comparing coverage by age group and race/ethnicity has been published previously (10). The same statistical methods were used for both seasons (2009–10 and 2010–11). Estimates were suppressed if the sample size was <30 or the relative standard error was >0.3. Student t tests were used to determine statistical significance in differences between groups and between 2009–10 and 2010–11 vaccination coverage levels with significance defined as p<0.05. Only statistically significant results are highlighted in this report.

Results

Overall, influenza vaccination coverage was two percentage points higher for the 2010–11 season versus the 2009–10 season (43.0% versus 41.2%, respectively), primarily because of an increase in vaccine coverage among children aged 6 months–17 years (51.0% versus 43.7%, respectively) (Table). Vaccine coverage increased significantly among four groups of children: Hispanic and non-Hispanic whites, blacks, and those of other/multiple races. During the 2010–11 seasons, compared with non-Hispanic white children, coverage among Hispanic, Asian/Pacific Islander, and children of other and multiple races was higher (Table).

Overall, influenza vaccination coverage among adults aged ≥18 years remained relatively stable, at 40.4% during 2009–10 and 40.5% during the 2010–11 influenza season (Table). Among those aged 18–49 years (regardless of risk status) and 50–64 years, coverage was similar in both seasons. However, among adults aged ≥65 years, coverage decreased from 69.6% to 66.6%.

During 2010–11, among all adults, including persons aged 18–49 overall, 50–64, and ≥65 years, coverage remained lower among non-Hispanic blacks (28.1%, 38.4%, and 56.1%, respectively) than among non-Hispanic whites (31.6%, 45.7%, 67.7%, respectively). Coverage also was lower among Hispanic adults aged 18–49 and 50–64 years (27.1% and 41.9%, respectively) than among non-Hispanic whites (31.6% and 45.7%, respectively). During 2010–11, coverage was similar among Hispanics and non-Hispanic whites aged ≥65 years; however, compared with 2009–10, coverage decreased by 4.0 percentage points among non-Hispanic whites and increased by 10.7 percentage points among Hispanics (Table).

Discussion

Overall, influenza vaccination coverage estimates were significantly higher during the 2010–11 season than during the 2009–10 season because of an increase in vaccinations among children. Coverage among non-Hispanic black and Hispanic children has improved, and is either similar to, or slightly higher than, coverage among non-Hispanic white children. Efforts to improve coverage are ongoing. The federally funded Vaccines for Children program provides vaccines at no cost to children who might not otherwise be vaccinated because of inability to pay (17). Community demand for influenza vaccination can be increased by client reminder and recall systems (18). Provider and systems-based interventions (e.g., provider assessment and feedback, and use of immunization information systems) also can increase vaccination coverage (http://www.thecommunityguide.org/vaccines/universally/index.html) (17,18).

Among adults aged ≥65 years, influenza vaccination coverage was lower among non-Hispanic blacks than all other racial/ethnic groups, suggesting that additional efforts to reach this population are needed. Interventions (18) to provide all ACIP recommended vaccinations throughout the lifespan could be a step toward increasing coverage and addressing disparities among adults.

The revised ACIP recommendations to vaccinate all persons aged ≥6 months were in place for the entire 2010–11 influenza season, but did not appear to have an effect on coverage among those aged 18–49 years (regardless of risk status) compared with the previous season. Additional promotion of or education about the expanded recommendations might increase coverage in this age group. Promising strategies might include 1) expanding access through nontraditional settings (e.g., pharmacy, workplace, and school venues) for vaccination to reach persons who might not visit a traditional provider during the flu season; 2) improving the use of evidence-based practices at medical sites (e.g., standing orders, reminder/recall notification, and provider recommendation) to ensure that all persons who visit a health-care provider during the flu season receive a vaccination recommendation and offer; or 3) using immunization information systems, also known as registries, at the point of clinical care and at the population level to guide clinical and public health vaccination decisions (18).

Limitations

The findings in this report are subject to at least five limitations. First, children aged 6 months to <9 years are recommended for up to 2 doses of vaccine depending on past vaccination history (11); however, this report only measured receipt of at least 1 dose for children of all ages. Second, the estimates are made on the basis of self-report for adults and parental-report for children, and were not validated by medical record reviews. Racial/ethnic disparities also might differ on the basis of parent versus provider report, child's age, and whether receipt of 1 dose or full vaccination status is measured; previous studies have shown racial/ethnic disparities in influenza vaccination coverage of children aged 6–23 months on the basis of provider-reported data for full vaccination; most children in this age group would need 2 doses to be considered fully vaccinated (19,20). Third, the sample might not be nationally representative because of incomplete sample frames (e.g., NIS and BRFSS surveys miss households without phones), and selection bias from survey nonresponse might remain after weighting adjustments (1,17,21,22). Fourth, misclassification of 2009 H1N1 vaccine for seasonal influenza vaccine, unique to this season, might have contributed to some overreporting. Finally, comparisons of estimates during 2009–10 and 2010–11 might be affected by different data sources used: NHFS and BRFSS for both children and adults for 2009–10, and NIS for children and BRFSS for adults in 2010–11.

Conclusion

Compared with the 2009–10 season, estimates for 2010–11 suggest that progress was made in increasing coverage among non-Hispanic white, black, Hispanic, and other and multiple race children. In contrast with the past, in which non-Hispanic white children generally had the highest coverage, estimates for both seasons indicated that Hispanic and A/PI children and those of other/multiple races had better coverage than non-Hispanic white children. Despite these improvements in coverage among historically underserved groups, Healthy People 2020 targets for influenza vaccination of children and adults—to increase the percentage of children aged 6 months through 17 years and adults aged ≥18 years vaccinated to 70%—were not achieved. Efforts are needed to continue improving coverage for all persons (18–23).

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