During six influenza epidemics in the United States from 1972 to 1981, influenza resulted in an average of 20,000 excess deaths per year; more than 80% of these deaths were among persons aged greater than or equal to 65 years (1). During the 1987-88 influenza season, widespread or regional outbreaks were reported from 44 states and the District of Columbia, and 86% of the pneumonia and influenza (P&I) deaths occurred in persons aged greater than or equal to65 years (2). Despite the continuing mortality caused by influenza among older adults, most do not receive annual immunization.

This report summarizes a population-based survey of influenza immunization levels among U.S. adults obtained through the Behavioral Risk Factor Surveillance System (BRFSS). The BRFSS is a state-based system that monitors self-reported risk behaviors. Multistage cluster design and random-digit dialing are used to conduct monthly telephone surveys of adults (aged greater than or equal to18 years) throughout the year (3). Respondents are selected randomly from all adults in each household.

In 1987, one question asking whether the respondent had received an influenza vaccination in the previous 12 months was added to the survey. n addition to questions on specific risk behaviors, the interviews included questions on respondents' demographic characteristics. Questions concerning health conditions that increase the risk for complications and death from influenza were not asked. Thirty-one states and the District of Columbia participated in the 1987 BRFSS. Results were weighted to each state's most recent adult population estimates by age, sex, and racial distribution, as well as by the respondent's probability of selection. Investigators used a specialized statistical package for multistage sample design to analyze findings.

In 1987, interviews were completed for 48,878 persons; 99.4% of the respondents stated they knew whether they had received an influenza vaccination in the previous 12 months. Because there was no difference in the proportion of respondents who reported receiving an influenza vaccination by month of interview, the data for the entire year were combined for analysis.

Reported influenza immunization levels varied by area and by age (Table 1). Of all participating states, 12% of respondents reported having received influenza vaccine in the previous 12 months: 7% of those aged 18-44 years, 11% of those aged 45-64 years, and 32% of those aged greater than or equal to65 years. The range of influenza vaccine coverage by age was 3%-18% (median 8%) among those aged 18-44 years; 7%-17% (median 12%) among those aged 45-64 years; and 24%-41% (median 34%) among those aged greater than or equal to65 years. The state-specific prevalence of all persons who reported having received influenza vaccine in the previous year ranged from 9% to 19% (median 13%) for the 32 areas in the BRFSS. Hawaii (19%) and New Mexico (18%) had the highest overall prevalence of self-reported influenza vaccine coverage, and New York (9%) and California (10%), the lowest. Among persons aged greater than or equal to65 years (for whom influenza vaccine is universally recommended), Montana (41%) and Nebraska and Ohio (40% each) had the highest self-reported coverage, and Rhode Island (24%) and the District of Columbia (25%), the lowest.

When gender differences were stratified by age group, men were more likely to report influenza immunization than were women (statistically significant difference) only in the group aged 18-44 years (Table 2). Black respondents reported higher influenza immunization levels than did white respondents among 18-44-year-olds, but among persons greater than or equal to65 years of age, whites reported higher levels than did blacks. Whites reported higher immunization levels than did Hispanics in the oldest age group (Table 2). Reported by: 1987 State Behavioral Risk Factor Surveillance System Coordinators. Div of Immunization, Center for Prevention Svcs; Div of Nutrition, Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: Influenza vaccine is recommended annually for persons with chronic cardiopulmonary disorders; residents of nursing homes and other chronic-care facilities; healthy adults greater than or equal to65 years of age; adults and children with renal dysfunction, metabolic diseases (including diabetes mellitus), severe anemia, or compromised immune function; children and teenagers receiving long-term aspirin therapy; health-care personnel caring for high-risk patients; and household contacts of high-risk persons (4-6). The vaccine may be up to 90% effective in preventing illness in healthy young adults and approximately 75% effective in reducing deaths from influenza and its complications among high-risk elderly persons living in institutions (1).

The 1990 health objectives for the nation set a target of 60% influenza vaccine coverage for high-risk populations, including persons aged greater than or equal to65 years (7). Based on the BRFSS data for 1987 and a review of national influenza immunization estimates for previous years, this objective is not likely to be met. Previous national estimates of influenza vaccine coverage have been based on two systems: 1) the United States Immunization Survey (U.S.I.S.) (discontinued after 1985) represented responses to questions regarding immunization with influenza and other vaccines, which had been added to the annual Current Population Survey conducted by the Bureau of the Census; and 2) the CDC Biologics Surveillance (a national estimate of the number of vaccine doses administered annually) is based on manufacturer-provided data on the net number of doses distributed nationwide (i.e., total number distributed minus the number returned). Based on U.S.I.S. data, the proportion of persons aged greater than or equal to65 years who reported having received influenza vaccine remained stable from 1978 through 1985, ranging from 19.6% to 23.5% (Figure 1). In 1985, the last year for which U.S.I.S. data are available, the rate was 22.6% (CDC, U.S.I.S., unpublished data, 1979-1985).

Data from the CDC Biologics Surveillance show that the net number of doses of trivalent influenza vaccine distributed from 1978 to 1986 averaged nearly 18.9 mllion, excluding 1980, when only 12.4 million doses were distributed (Figure 2) (8). In 1987, 27.1 million doses were distributed, the largest number since 1976 (CDC, unpublished data, 1987) and greater than or equal to25% more than the number of doses distributed in any subsequent year. These data do not provide any information on population coverage levels. However, the mean overall coverage prevalence of 32.2% among adults aged greater than or equal to65 years obtained in the states participating in the 1987 BRFSS survey (Table 2) suggests that the increased distribution of influenza vaccine in 1987 may have been associated with an increase in influenza vaccine coverage among older adults in the United States.

Several limitations of the BRFSS survey must be considered when the data for influenza immunization coverage are interpreted. The data were collected from 32 nonrandomly selected states and, therefore, may not be used as estimates for the entire U.S. population. Although the results were weighted for each state's most recent adult population estimate by age, sex, and race, bias of unknown direction and magnitude may remain if immunization levels differ among households without telephones, persons who refused to participate, and persons who could not be contacted. In addition, these data were self-reports of immunization status and were not verified through provider records. However, previous experience has shown that persons correctly recall receiving a "flu shot" within the preceding year (CDC, unpublished data, 1988). Finally, because no information was collected about medical conditions that increase the risk for complications or death from influenza, it is not possible to evaluate coverage among younger adults with these high-risk conditions, for whom influenza vaccine is also recommended. Further analysis of these data will include examination of the relationship between vaccination and other risk-reduction behavior.

Despite these limitations, the data are useful in efforts to guide improved influenza vaccine delivery. Evaluation of states with higher vaccine coverage may identify factors that promote influenza vaccination. Influenza prevention is carried out primarily by private-sector providers and state and local health agencies. Influenza vaccine coverage has been improved in some state and local programs through activities such as collaboration with third-party payers and other private organizations, and state and county purchase of vaccine (9). Two states, Delaware and South Dakota, have implemented regulations requiring nursing homes to provide influenza vaccination for residents as a condition for licensure. In addition, CDC and the Health Care Financing Administration are coordinating nine demonstration projects to assess the cost-effectiveness of furnishing influenza vaccine to Medicare Part B beneficiaries.

As many as 75% of persons at high risk for influenza orwho die from P&I may have received care in outpatient clinics before their illness but did not receive influenza vaccination (1). Because one of the most important factors in a person's decision to receive influenza vaccine is the recommendation by a health-care provider to be vaccinated (1,10), increased efforts of health-care providers to recommend influenza immunization could improve influenza vaccine coverage. Health-care providers should incorporate annual influenza immunization into their practices and offer this and all other vaccines appropriate for adults (pneumococcal, hepatitis B, measles, mumps, and rubella vaccines, and diphtheria and tetanus toxoids) (5,6) at every appropriate opportunity.

References

1. Williams WW, Hickson MA, Kane MA, Kendal AP, Spika JS, Hinman AR. Immunization policies and vaccine coverage among adults: the risk for missed opportunities. Ann Intern Med 1988;108:616-25. 2.CDC. Influenza--United States, 1987-88 season. MMWR 1988;37:497-503. 3.CDC. Behavioral risk factor surveillance--selected states, 1986. MMWR 1987;36:252-4. 4.ACIP. Prevention and control of influenza. MMWR 1988;37:361-4,369-73. 5.ACIP. Adult immunization: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1984;33(suppl 1S). 6.Committee on Immunization. Guide for adult immunization. Philadelphia: American College of Physicians, Council of Medical Societies, 1985. 7.Public Health Service. Promoting health/preventing disease: objectives for the nation. Atlanta: US Department of Health and Human Services, Public Health Service, 1980. 8.CDC. Biologics surveillance. Atlanta: US Department of Health and Human Services, Public Health Service, 1978-1986. 9.CDC. State and local influenza immunization program activities. MMWR 1988;37:705-7. 10.CDC. Adult immunization: knowledge, attitudes, and practices--DeKalb and Fulton Counties, Georgia, 1988. MMWR 1988;37:657-61.

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