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Increasing Influenza Vaccination Rates for Medicare Beneficiaries -- Montana and Wyoming, 1994

Approximately 20,000 influenza-associated deaths occurred during each of 10 different epidemics in the United States during 1972-1991; most (greater than 90%) of the deaths attributed to pneumonia and influenza occurred among persons aged greater than or equal to 65 years (1). Although Medicare has provided reimbursement for influenza vaccination since 1993, the Health Care Financing Administration (HCFA) received billing claims for influenza vaccination for the 1993-94 and 1994-95 influenza seasons for only 35% and 38% of Medicare beneficiaries, respectively (2) (HCFA, unpublished data, 1995). This report describes the impact of an intervention project in September 1994 in which individual Medicare beneficiaries aged greater than or equal to 65 years in Montana and Wyoming were contacted and encouraged to receive influenza vaccination.

The project was conducted by the Montana-Wyoming Foundation for Medical Care (MWFMC) in collaboration with HCFA. During 1994, the numbers of persons who were Medicare beneficiaries in Montana and in Wyoming were 130,000 and 60,000, respectively. The two states were divided into 40 geographic regions defined by zip code aggregates (24 in Montana, 16 in Wyoming); in each state, four regions were randomly selected as intervention sites. During September 23-30, MWFMC sent individual letters and an informational brochure to Medicare beneficiaries with mailing addresses in the eight intervention regions: in two regions (total population: 19,850) in each state, beneficiaries received a personalized letter from the MWFMC medical director encouraging them to obtain vaccination, and beneficiaries in the other two regions (total population: 21,250) in each state received a form letter from the MWFMC encouraging them to obtain vaccination. In addition, during October 1994, public and private organizations, including HCFA, implemented measures to increase influenza vaccination coverage in all regions, including public service announcements and notices to health-care providers.

Vaccination rates in the intervention regions were compared with those in the remaining regions for October 1-December 31 in both 1993 and 1994 using influenza vaccination claims submitted to HCFA. Approximately 90% of influenza vaccination claims submitted to HCFA are for vaccinations provided from October 1 through December 31. Medicare pays for influenza vaccination for beneficiaries enrolled in Part B. This analysis was restricted to those who were alive and continuously enrolled in Part B during the study period; approximately 96% of persons aged greater than or equal to 65 years in the United States are enrolled in Medicare Part B. A beneficiary was considered to have received an influenza vaccination if at least one bill for either the influenza vaccine or administration of the vaccine was submitted for the study period. A logistic regression model was used to examine the relation between receipt of both a letter and an influenza vaccination; EGRET software was used to adjust for confounding variables and conduct statistical testing.

From 1993 through 1994, influenza vaccination rates increased in all regions of Montana and Wyoming regardless of intervention status. However, overall increases in influenza vaccination rates were greater in intervention regions across both states than in nonintervention regions by 6.1 percentage points (95% confidence interval {CI}=5.5-6.7). In Montana, the influenza vaccination rate for beneficiaries who received letters increased 8.7 percentage points (from 41.2% to 49.9% among those who received a personal letter) and 6.5 percentage points (from 46.0% to 52.5% among those who received a form letter) compared with 4.4 percentage points (from 42.3% to 46.7%) for beneficiaries who did not receive letters. The crude rate comparisons were statistically significant (personal letter versus no letter=1.1 {95% CI=1.1-1.2} and form letter versus no letter=1.3 {95% CI=1.2-1.3}). In Wyoming, the rate increased 18.9 percentage points (from 23.8% to 42.7% among those who received a personal letter) and 19.9 percentage points (from 20.5% to 40.4% among those who received a form letter) for those receiving letters compared with 11.5 percentage points (from 21.6% to 33.1%) for beneficiaries not receiving letters. The crude rate comparisons were statistically significant (personal letter versus no letter=1.5 {95% CI=1.4-1.6} and form letter versus no letter=1.4 {95% CI=1.3-1.4}).

The strongest predictor for a billing claim for vaccination in 1994 was a claim for vaccination in 1993 (odds ratio {OR}=8.1 {95% CI=7.9-8.4} for beneficiaries vaccinated in 1993 versus those not vaccinated in 1993). In addition, after adjusting for age, sex, and 1993 vaccination status, beneficiaries who received a letter were significantly more likely to receive an influenza vaccination than beneficiaries who did not (OR=1.3; 95% CI=1.3-1.4). Beneficiaries who received a letter from MWFMC were more likely to have a claim for vaccination than those who did not receive a letter both among persons who were vaccinated in 1993 (OR=1.2; 95% CI=1.2-1.3) and those who were not vaccinated in 1993 (OR=1.4; 95% CI=1.3 to 1.4). The likelihood of vaccination was similar for persons who received a personal letter and for those who received a form letter. Age was also an important predictor for a billing claim for vaccination in 1994 (beneficiaries aged greater than or equal to 70 years were more likely than those aged 65-69 years to have a billing claim).

Reported by: JW McMahon, MD, JR Hillman, MD, M McInerney, PhD, Montana-Wyoming Foundation for Medical Care, Helena. MJ Kileen, MD, C Christensen, PhD, Health Care Financing Administration, Regional Office, Seattle, Washington. Adult Vaccine Preventable Diseases Br, Epidemiology and Surveillance Div, National Immunization Program, CDC.

Editorial Note

Editorial Note: Influenza vaccination levels among elderly persons in the United States increased from 1989 (33%) through 1993 (52%) (3), probably reflecting greater acceptance of preventive medical services by practitioners and patients and increased delivery of vaccine by health-care providers and sources other than physicians (e.g., visiting-nurse and home-health agencies) (3). In addition, the findings in this report suggest that the initiation of Medicare reimbursement for influenza vaccination in 1993 may have contributed to increased rates in Montana and Wyoming, although this intervention also may have increased submission of Medicare claims for persons who had already been receiving influenza vaccine. The intervention project also indicated that prior influenza vaccination, documented by Medicare claims data, was the strongest predictor of current vaccination -- a finding consistent with previous reports (4). In addition, the increase in vaccination rates among those who received a letter is similar to the effect of the Medicare Influenza Vaccine Demonstration program in 1990 and 1991, during which a letter to all beneficiaries in parts of 10 states was the most important motivator for vaccination (5).

The Montana and Wyoming intervention resulted in a statistically significant, although modest, improvement in vaccination levels. Other client-oriented interventions (e.g., letter or postcard reminders) have improved influenza vaccination levels by an average of 12% (6). Provider- (e.g., chart reminders and reminders directly to physicians) and system-oriented interventions (e.g., standing orders to nurses) also have been effective in increasing influenza vaccination levels (18% and 39%, respectively) for patients who could be directly identified in providers' health record systems (6). In addition, combinations of client and provider strategies have been documented to be more effective than client-based strategies alone (6). Future interventions to improve influenza vaccination levels in the Medicare population could employ a combination of strategies directed toward patients, providers, and systems to assure more effective means of providing influenza vaccination are used.


  1. CDC. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1995;44(no. RR-3).

  2. Health Care Financing Administration. 1993 Influenza immunizations paid for by Medicare: state and county rates. Baltimore, Maryland: Health Care Financing Administration, 1994.

  3. CDC. Influenza and pneumococcal vaccination coverage levels among persons aged greater than or equal to 65 years -- United States, 1973-1993. MMWR 1995;44:506-7,513-5.

  4. Nichol KL, Lofgren RP, Gapinski J. Influenza vaccination: knowledge, attitudes, and behavior among high-risk outpatients. Arch Intern Med 1992;152:106-10.

  5. Anderson K, Teske R, Dini E, Strikas R. Improving influenza vaccination coverage in the Medicare population. In: Hannoun C, Kendal AP, Klenk HD, Ruben FL, eds. Options for the control of influenza II. Amsterdam, Netherlands: Elsevier, 1993:109-13.

  6. Gyorkos TW, Tannenbaum TN, Abrahamowicz, M, et al. Evaluation of the effectiveness of immunization delivery methods. Can J Public Health 1994;(suppl 1):S14-S30.

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