Influenza Vaccination Coverage Among Persons with Asthma --- United States, 2005--06 Influenza Season

During 2006, approximately 6.8 million (9.3%) U.S. children and 16.1 million (7.3%) U.S. adults were reported to have asthma (1,2). Since 1964, the Advisory Committee on Immunization Practices (ACIP) has recommended influenza vaccination of all persons with asthma because of the higher risk for medical complications from influenza for those persons (3,4). Influenza vaccination coverage of persons with asthma varies by age group and remains below Healthy People 2010 targets of 60% coverage of persons aged 18--64 years with high-risk conditions (14-29c) and 90% of all persons aged >65 years (14-29a) (5--7). Influenza vaccination rates of children and older adults with asthma have not been well studied. Using 2006 National Health Interview Survey (NHIS) data, this report provides the first examination of influenza vaccination rates and related factors across a national sample of persons with asthma aged >2 years. The results indicated that 36.2% received influenza vaccination during the 2005--06 influenza season. Vaccination rates remained below target levels among all subgroups examined, including those reporting the greatest number of health-care visits in the past 12 months. The results of this study indicate that influenza vaccination coverage of all persons with asthma can be improved by increasing access to health care and using opportunities for vaccination during health-care visits.

NHIS is an ongoing, nationally representative, in-person household interview survey of the civilian, noninstitutionalized population of the United States. Beginning with the 2004--05 influenza season, influenza vaccination questions were included in the child questionnaire portion of the NHIS. Because of an influenza vaccine shortage during the 2004--05 season, 2005--06 was the first influenza season for which the NHIS was able to provide an estimate of influenza vaccination rates among children with asthma in a nonshortage season. This report examines NHIS data on influenza vaccination among all persons with asthma aged >2 years during the 2004--05 and 2005--06 influenza seasons and identifies characteristics associated with vaccination coverage. Age subgroups were chosen for convenient comparison with previously published Behavioral Risk Factor Surveillance System and NHIS results (5). Because diagnoses of asthma in children aged <2 years are considered unreliable, and to be consistent with other reports, the <2 years age group was excluded from this report (6).

To ensure that included respondents had equal opportunity for vaccination, only responses for persons who were within the stated age range for the entire influenza season (September 2005--February 2006) were included; furthermore, only responses from interviews that occurred following the influenza season (i.e., interviews conducted during March--August 2006) were included in the analysis to ensure that only vaccinations given for the 2005--06 season were counted. In addition, only persons who reported the month of their most recent vaccination to be in the period September 2005--February 2006 were considered vaccinated for the 2005--06 season. The same inclusion criteria were applied to 2004--05 influenza season data.

For the 2004--05 and 2005--06 seasons, influenza vaccination status was stratified by characteristics reported to influence likelihood of vaccination, including age group, race/ethnicity, income, health insurance coverage, number of health-care visits, and possession of a usual place of health care (5,6). Differences in coverage were compared by chi-square test for within-year comparisons and z-test for comparisons in coverage across influenza seasons, with statistical significance defined as p<0.05.

Of the 15,295 survey participants aged >2 years for the entire 2005--06 influenza season, 1,277 (8.3%) reported current asthma, of whom 29 (2.2%) were excluded from further analysis because of incomplete answers regarding vaccination. Of the remaining 1,248 participants with asthma, 455 reported receiving influenza vaccinations, but 24 (5.3%) had received their vaccination before September 2005 or after February 2006 and were counted as unvaccinated for the 2005--06 season. Influenza vaccination coverage of persons aged >2 years with asthma in the 2005--06 influenza season was 36.2%, compared with 23.9% among those without current asthma (p<0.001) (Table 1) . Both coverage rates represent significant increases from the 2004--05 season, in which respective rates were 31.5% (95% confidence interval [CI] = 28.9--34.3, p<0.05) and 16.7% (CI = 16.4--17.4, p<0.001). Among persons with asthma, those aged 50--64 years and >65 years had the highest influenza vaccination coverage in 2005--06 (48.6% and 75.7%, respectively). Among all age subgroups, persons with asthma were more likely to receive influenza vaccination than those without asthma (Table 1).

Persons without a usual place for health care were more likely to remain unvaccinated during the 2005--06 season (89.6%, CI = 79.3--95.1) than those with at least one usual place for health care (61.3%, CI = 57.5--65.0; p<0.001); this difference persisted when limited to the insured (81.8%, CI = 58.6--93.5; and 59.2%, CI = 55.1--63.2, respectively; p<0.03). Influenza vaccination coverage was higher among participants with health insurance coverage (39.9%) than among the uninsured (14.5%, p<0.001) (Table 2). Vaccination coverage increased from 33.8% to 39.9% (p<0.02) among insured persons with asthma from the vaccine shortage season of 2004--05 to the season of regular supply in 2005--06, but coverage did not increase among those without insurance (13.5% to 14.5%, p=0.8). From the 2004--05 to the 2005--06 influenza seasons, vaccination rates increased significantly only among persons in families earning annual incomes >4.5 times the federal poverty level (Table 2).

The likelihood of receiving an influenza vaccination increased with increasing numbers of health-care visits, defined as a visit to a doctor's office, clinic, or other place of health care, but not counting hospitalizations, emergency department visits, dental or home visits, or telephone calls (Table 3). Coverage ranged from 17.6% in persons with asthma reporting one visit or less to 50.8% in those reporting 10 or more visits. Stratified by number of health-care visits, influenza vaccination coverage was significantly higher among persons with asthma than among those without for each stratum, except for the 6--9 health-care visits stratum. Stratified by available measures of asthma severity, coverage was not different among those with acute exacerbations. Vaccination coverage was 41.8% among persons with at least one emergency department or urgent care visit for asthma within the preceding 12 months and 35.4% with no such visits (p=0.2). Influenza vaccination coverage did not differ significantly between persons with asthma who had an exacerbation in the past 12 months and those who did not (37.5% versus 34.8%, p=0.5). Vaccination coverage also did not differ significantly by race/ethnicity, ranging from 30.8% of Hispanics (CI = 24.4--38.1) to 37.9% (CI = 33.4--42.5) of non-Hispanic whites (p=0.09).

Reported by: CB Ligon, RA Rudd, MSPH, DB Callahan, MD, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; GL Euler, DrPH, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC

Editorial Note:

This report presents the first estimates of influenza vaccination coverage in the United States among the civilian, noninstitutionalized population of persons with asthma and reinforces the need to increase vaccination throughout this at-risk population. Health-care visits provide an opportunity for vaccination, but even among persons with the highest number of visits, nearly half remained unvaccinated in the 2005--06 influenza season. Even so, access to health care is an important factor associated with receiving influenza vaccination. Persons with asthma who had health insurance had a greater rate of influenza vaccination than did those who lacked insurance. Likewise, the vaccination rate for persons with asthma who had a usual place for health care was significantly greater than the rate for those who did not have a regular place for health care. After the vaccine shortage of the 2004--05 influenza season, vaccination coverage of persons with asthma in 2005--06 failed to improve among households with the lowest incomes, among persons without health insurance, and among persons without a regular place for medical care, emphasizing the need for interventions that include the medically underserved.

During the 2005--06 influenza season, the oldest age groups (50--64 years and >65 years) had the highest vaccination coverage. Influenza vaccination is recommended for both age groups, regardless of asthma status, because the influenza-related death rate increases sharply among older adults (3). In February 2006, ACIP recommended that all children aged 24--59 months be vaccinated against influenza, regardless of risk status. Examination of the 2007 NHIS data could determine whether the expanded recommendation affected coverage among the subset of children with asthma, who already had been recommended for vaccination under previous guidelines. Because ACIP voted in February 2008 to recommend influenza vaccination for all children, data soon will be available to also study the effects on coverage for older children.*

The findings in this report are subject to at least three limitations. First, the sample size of the survey (34,112 adults and children, 2,700 of whom reported having current asthma) limits reliable identification of patterns among subgroups of persons with asthma potentially of interest but smaller in number than the subgroups examined here. Second, determination of vaccination status in NHIS is made by self-report, which introduces recall bias and likely overestimation of vaccination rates (8). Finally, NHIS does not ascertain whether a child received a second vaccine dose, as is recommended by ACIP for children aged 6 months to 8 years who previously have not received the influenza vaccination; therefore, NHIS overestimates full coverage for this age group (3).

The findings in this report emphasize the need for measures to uniformly increase influenza vaccination rates among persons with asthma. Interventions that target patients, health-care access, and health-care providers have demonstrated benefits in similar settings and should be implemented to improve influenza vaccination coverage. Such interventions include automated reminders, standing orders, multicomponent educational programs, reduction of travel distances or out-of-pocket vaccine costs, and provider performance feedback (9). Persons with inadequate access to health care and those treated at multiple facilities would be less likely to miss opportunities for vaccination if they consistently sought care at a single medical facility. That continuity of care could reduce the diffusion of responsibility that occurs when patients are treated at multiple health-care facilities (10). Providing vaccination through at least January and February of the influenza season can further reduce missed opportunities for effective vaccination of persons in this group at high risk.

References

1. Bloom B, Cohen RA. Summary health statistics for U.S. children: National Health Interview Survey, 2006. Vital Health Stat 2007;10(234).
2. Pleis JR, Lethbridge-Çejku M. Summary health statistics for U.S. adults: National Health Interview Survey, 2006. Vital Health Stat 2007;10(235).
3. CDC. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2007. MMWR 2007;56(No. RR-6).
4. CDC. Advisory Committee on Immunization Practices: recommendations for influenza immunization and control in the civilian population. Influenza Surveillance Report 1964;80:8--11.
5. CDC. Self-reported influenza vaccination coverage trends 1989--2006 among adults by age group, risk group, race/ethnicity, health-care worker status, and pregnancy status, United States, National Health Interview Survey (NHIS). Available at http://www.cdc.gov/flu/professionals/vaccination/pdf/vaccinetrend.pdf.
6. CDC. Influenza vaccination coverage among children with asthma---United States, 2004--05 influenza season. MMWR 2007;56:193--6.
7. US Department of Health and Human Services. Healthy people 2010 (conference ed, in 2 vols). Washington, DC: US Department of Health and Human Services; 2000. Available at http://www.healthypeople.gov.
8. Mangtani P, Shah A, Roberts JA. Validation of influenza and pneumococcal vaccine status in adults based on self-report. Epidemiol Infect 2007;135:139--43.
9. Task Force on Community Preventive Services. Recommendations regarding interventions to improve vaccination coverage in children, adolescents, and adults. Am J Prev Med 2000;18(1 Suppl):92--6.
10. Smith PJ, Santoli JM, Chu SY, Ochoa DQ, Rodewald LE. The association between having a medical home and vaccination coverage among children eligible for the Vaccines for Children program. Pediatrics 2005;116:130--9.

* Available at http://www.cdc.gov/vaccines/recs/provisional/downloads/flu-3-21-08-508.pdf.

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Date last reviewed: 6/19/2008