Influenza Vaccination Coverage Among Persons Aged 50--64 Years Enrolled in Commercial Managed Health-Care Plans --- United States, 2003--04 and 2004--05 Influenza Seasons

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To combat an unexpected shortage of influenza vaccine in the fall of 2004, CDC issued guidance to direct available vaccine supplies to persons in designated priority groups (e.g., persons aged >65 years, persons with certain health conditions, health-care workers, and close contacts of persons at high risk for complications from influenza) (1,2). Analyses of influenza vaccination coverage for the 2004--05 influenza season indicated that coverage levels for adults in priority groups nearly reached the levels of previous years, whereas coverage levels among adults not in priority groups were approximately half the levels of the 2003--04 season (3). These findings suggested that national public health actions to direct available vaccine supply to persons at high risk for complications from influenza during the supply disruption were successful. To assess influenza vaccination coverage among persons aged 50--64 years for the 2004--05 influenza season relative to the 2003-04 season and to estimate the effect of shortages on selected subgroups, the National Committee for Quality Assurance* (NCQA) analyzed data from a survey of persons enrolled in commercial managed care health plans. This report summarizes the findings of that analysis, which indicated that, although vaccination coverage declined substantially from 2003--04 to 2004--05 among all subgroups in this age range, respondents who were older or who reported poorer health status exhibited smaller relative declines in vaccination coverage between the two seasons.

Data for this analysis are from the Consumer Assessment of Health Plans (CAHPS^™) survey, a national survey of members of commercial health plans. This annual survey samples the membership of more than 250 managed care organizations (MCOs) with approximately 70 million members, representing more than 90% of the total commercial MCO membership in the United States. Independent samples are selected from each plan every year. The survey is conducted during March--May by independent survey research firms trained and monitored by NCQA to ensure compliance with a common written protocol. The survey uses a mixed mail/telephone protocol that yields an average response rate of 40%, a typical response rate for surveys of the commercially insured population. These data are used as the basis for a performance measure in the Health Plan Employer Data and Information Set (HEDIS^™) that assesses the proportion of persons aged 50--64 years who received an influenza vaccination during the preceding year. The 50--64 years age range is consistent with the CDC recommendation for universal influenza vaccination during non-shortage years (4).

Members eligible for the influenza vaccination measure must have been aged 50--64 years as of September 1 of the calendar year preceding the survey, enrolled in the MCO at the time of the survey, and continuously enrolled in the same MCO for at least 12 months. Vaccination coverage is determined by the percentage of affirmative responses to the question, "Have you had a flu shot since September 1, YYYY?" where YYYY is the year prior preceding the survey year. Responses to the question about influenza vaccination totaled 55,510 for 2004 and 61,460 for 2005. The questionnaire also included questions about age, sex, education, race, and Hispanic ethnicity and an overall health-status question, "In general, how would you rate your overall health now?"

Influenza vaccination coverage was analyzed for demographic and self-reported--health subgroups and compared by season. To test for possible confounding among these characteristics, NCQA estimated a multiple logistic regression model with receipt of vaccination as the dependent variable and indicator variables for the subgroups and interactions of the subgroups with the season as independent variables. Results were not weighted to account for differences in the sampling proportion across plans because the sampling proportion was uncorrelated with influenza vaccination coverage.

The findings of this analysis indicated that, from 2003--04 to 2004--05, vaccination coverage for the surveyed population decreased from 52.4% (95% confidence interval [CI] = 52.0%--52.8%) to 28.1% (CI = 27.7%--28.4%), a decrease of approximately 46% (Table). All eight regions of the United States experienced similar decreases, with the largest percentage decrease occurring in the Mid-Atlantic region (50.5%) and the smallest in New England (43.9%). Vaccination coverage increased with age, from 45.6% for persons aged 50--54 years to 60.1% for persons aged 60--64 years in 2003--04, with similar relative increases in 2004--05. Persons aged 50--54 years experienced the largest percentage decrease (51.3% compared with 40.9% for persons aged 60--64 years). Compared with women, men had lower vaccination coverage for 2003--04 (50.0% versus 53.9% for women), with a larger percentage decrease in 2004--05 (49.2% for men versus 44.2% for women). For both years, respondents with a high school education or greater had higher vaccination coverage than those with less than a high school education. However, this difference decreased in 2004--05 because of larger declines in vaccination coverage for those with a high school education or greater.

Self-reported health status had a substantial effect on vaccination coverage, with healthier respondents less likely to receive a vaccination. During 2003--04, respondents who described their health as "excellent" had vaccination coverage of 47.9% (CI = 46.8%--49.0%) compared with 58.6% (CI = 55.4%--61.6%) among those who reported having "poor" health. This difference increased in 2004--05, with coverage for respondents who reported being in excellent health decreasing to 23.2% (CI = 22.4%--24.1%), a decline of more than half (51.6%); coverage for respondents of self-reported poor health decreased to 44.8% (CI = 41.6%--47.9%), a decline of less than one fourth (23.5%).

During 2003--04, Hispanics had vaccination coverage of 44.8% (CI = 43.0%--46.5%) versus 53.0% (CI = 52.5%--53.4%) for non-Hispanics. In 2004--05, coverage for Hispanics decreased by less (44.4%) than that for non-Hispanics (46.6%). Similarly, coverage for whites and Native Hawaiians/ Pacific Islanders was highest in 2003--04 (approximately 54%) but declined the most (47.1% and 48.3%, respectively) in 2004--05. Among all races, coverage for blacks was lowest in 2003--04 at 38.6% (CI = 37.1%--40.0%) and declined by 39.1% in 2004--05, to 23.5% (CI = 22.3%--24.7%). Multiple logistic regression analysis confirmed the independent effects of these factors on vaccine availability.

Reported by: RE Mardon, PhD, LG Pawlson, MD, SH Scholle, DrPH, National Committee for Quality Assurance, Washington, DC.

Editorial Note:

Data from CAHPS provide insight into the effects of the fall 2004 influenza vaccine shortage on vaccination coverage for a population at low risk for complications from influenza. Overall, the limited availability of vaccine, the media attention to the problem, and calls from public health authorities to direct available supplies to persons at high risk appear to have resulted in decreases in vaccination coverage among MCO enrollees compared with the preceding season. These decreases were consistent across all eight geographic regions, suggesting that available supplies were distributed uniformly across the United States, although variations within smaller geographic areas might have been more extreme.

Respondents who were older or who reported poorer health status exhibited smaller relative reductions in vaccination coverage; this suggests that efforts to target vaccination to higher-risk members of the survey population were somewhat successful. However, CAHPS data indicate that substantial reductions in vaccination coverage occurred among commercially insured persons with fair or poor health status.

The findings of this report are subject to at least four limitations. First, CAHPS data are subject to recall bias regarding receipt of an influenza vaccination. Second, with a response rate of only 40%, the data are subject to nonresponse bias. Third, the commercially insured managed care population might differ from other populations of interest, thereby limiting the generalizability of the results. Finally, self-reported health status might differ from clinical assessments of health, thereby limiting the ability to determine whether survey respondents with fair or poor self-reported health status met the CDC definition of high risk for complications from influenza and were therefore members of a priority group for vaccination (1,2).

Further research into medical conditions associated with self-reported fair or poor health status might provide insight into the characteristics and health conditions of these persons, providing an additional tool for managing the public health response to future influenza vaccine shortages.

A simple self-assessment question about health status administered in a waiting room might help clinicians and public health authorities identify persons at high risk and target vaccine to priority groups during vaccine shortages.

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