Persons with underlying health-risk conditions such as asthma, bronchitis, emphysema, chronic obstructive pulmonary disease (COPD), heart disease, renal disease, diabetes, and cancer are known to be at substantially increased risk for serious complications from influenza (1-3). Vaccination of persons with high-risk conditions is a key public health strategy in preventing influenza-related morbidity and mortality in the United States (2). Optimal use of vaccination strategies can not only reduce influenza-related morbidity and mortality but can also minimize missed work days due to illness (2). Persons with high-risk conditions were recommended for annual influenza vaccination by the Public Health Service as early as 1960 (4). Prior to 2010, the Advisory Committee on Immunization Practices (ACIP) recommended yearly vaccination for adults ≥ 50 years and adults 18-49 years with high-risk conditions (5). Since the 2010-11 season, the ACIP has recommended annual influenza vaccination for all adults (1, 2, 5).

Before Healthy People 2020 influenza vaccination objectives were consolidated following the ACIP recommendation for universal vaccination of adults, the annual influenza vaccination target for adults 18-64 years with high-risk conditions was 90%. The current revised vaccination target for all adults ≥18 years is 70% (6); however, ACIP continues to emphasize that persons with high-risk conditions should be a focus of vaccination efforts (5). Despite the long-standing ACIP recommendations, vaccination levels among persons with medical conditions that increase risk for complications from influenza have remained suboptimal (7-11). To evaluate the impact of the current adult influenza vaccination program in the United States for persons with high-risk conditions, we assessed national influenza vaccination coverage and potential missed opportunities for vaccination among adults 18-64 years with underlying high-risk conditions using data from the National Health Interview Survey (NHIS). We also evaluated demographic and access-to-care factors associated with receipt of influenza vaccination to identify potential strategies to improve vaccination coverage.

We analyzed data from the 2012 and 2013 NHIS. NHIS is a probability based annual household survey conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention (12-13). The survey has four main modules: the household composition section, family core, sample adult core, and sample child core. In the sample adult core, one adult per sampled family was randomly selected and asked to complete the sample adult questionnaire, including questions about receipt of influenza vaccination. In 2012 and 2013, the final response rates for the sample adult core were 61.2% for both years (12-13).

We defined high-risk persons as individuals who self-reported one or more of the following: ever being told by a physician they had diabetes, emphysema, COPD, coronary heart disease, angina, heart attack or other heart condition; being diagnosed with cancer in the past 12 months (excluding non-melanoma skin cancer) or ever being told by a physician they have lymphoma, leukemia or blood cancer; during the past 12 months, being told by a physician they have chronic bronchitis or weak or failing kidneys; or reporting an asthma episode or attack in the past 12 months. Poverty status was defined as a total family income of <$23,492, and <23,624 for a family of four for 2012 and 2013, respectively, using poverty thresholds published by the U.S. Census Bureau (14).

SUDAAN (Software for the statistical analysis of correlated data, Research Triangle Institute, Research Triangle Park, NC, version 10.01) was used to calculate point estimates and 95% confidence intervals (CIs). In bivariate analyses, we assessed influenza vaccination among adults 18-64 years with high-risk conditions stratified by demographic and access-to-care variables. Chi-square and t-tests were used to determine differences between groups with statistical significance at p < 0.05. To better assess seasonal influenza vaccination coverage, we reported coverage restricted to individuals interviewed during August 2012 through June 2013, and vaccinated during July 2012 through May 2013 using the Kaplan-Meier survival analysis procedure. Multivariable logistic regression and predictive marginal models were used to generate adjusted prevalence ratios and identify variables independently associated with reported receipt of influenza vaccination in the past 12 months (15, 16). All variables used in the bivariate analysis were included in the full multivariable model. To assess potential missed opportunities for influenza vaccination among adults with high-risk conditions, we calculated the proportions of persons who reported not receiving influenza vaccination in the 2012-13 influenza season by selected health care access characteristics.

Table 1 shows the baseline demographic characteristics of the study population.

The overall influenza vaccination coverage for the 2012-13 season among adults 18-64 years with high-risk conditions was 49.5%. Vaccination coverage for the 2012-13 season among adults with high-risk conditions was significantly lower among adults 18-49 years at 39.0% compared with 59.3% for adults 50-64 years (Table 2). Vaccination coverage for adults 18-64 years with high-risk conditions was 49.0% for non-Hispanic whites, 45.8% for non-Hispanic blacks, 49.4% for Hispanics, 65.9% for Asians, and 60.6% for those reporting other race (Table 2). Coverage was significantly higher among Asians compared with non-Hispanic whites (p<0.05) (Table 2). Coverage for adults 18-64 years with high-risk conditions was significantly higher among adults with at least some college education, who were employed, and living at or above poverty level (Table 2) (p<0.05). Additionally, coverage was significantly lower among adults who were never married, and those who were born outside the United States and were in the United States less than 10 years (Table 2) (p<0.05).

Among adults 18-64 years with high-risk conditions, vaccination coverage was higher for those who had any physician contacts during the past year compared with those with none, and increased with higher numbers of physician contacts. There was almost a 40 percentage-point difference in proportion vaccinated between those who had no physician contacts and those who had 10 or more physician contacts in the past year (Table 2). Persons who had been hospitalized in the past year were significantly more likely to have received influenza vaccination than those who were not. There was a 38 percentage-point difference in vaccination coverage between those who had a regular physician for health care and those who did not have one. Coverage was significantly higher (p<0.05) among adults with health insurance (55.1%) compared with those without health insurance (23.9%) and among adults who had ever received pneumococcal vaccination (73.4%) compared with those who had not (38.7%) (p<0.05 for both comparisons) (Table 2). Vaccination coverage was significantly higher among adults 50-64 years compared with adults 18-49 years across most socio-demographic and access-to-care characteristics (Table 2).

In multivariable analysis, among adults 18-64 years with high-risk conditions, older age, being female, Hispanic ethnicity or Asian race, having one or more physician visits, a regular physician for health care, health insurance, and having ever received pneumococcal vaccination were independently associated with a higher likelihood of influenza vaccination. Being widowed/divorced/separated and not being employed were independently associated with a lower likelihood of influenza vaccination (Table 3). Among adults 18-49 years with high-risk conditions, characteristics independently associated with a higher likelihood of vaccination were similar to those for 18-64 years. Never having been married and not being employed were independently associated with a lower likelihood of vaccination (Table 3). Among adults 50-64 years with high-risk conditions, Hispanic ethnicity, having two or more physician visits, a regular physician for health care, health insurance, and having ever received pneumococcal vaccination were independently associated with a higher likelihood of vaccination (Table 3).

Among adults 18-64 years, influenza vaccination coverage in the 2012-13 season was 49.5% among those with at least one high-risk condition, 59.5% among those with at least two high-risk conditions, 46.2% among those with lung disease, 50.5% among those with heart disease, 58.0% among those with diabetes, 62.5% among those with renal disease, and 56.4% among those with cancer (Table 4). Additionally, most condition-specific vaccination coverage was significantly higher among persons 50-64 years compared with persons 18-49 years (Table 4).

Potential missed opportunities for influenza vaccination were also evaluated. Among adults 18-64 years with at least one high-risk condition who reported not receiving influenza vaccination in the 2012-13 season, 87.3% had one or more physician contacts in the last 12 months, 15.2% were hospitalized in past year, and 31.7% had visited an emergency room (ER). Overall, 90.1% reported at least one visit to a health care setting where vaccination could have been provided. Among persons reporting ≥ 2 ER visits, the proportion was significantly higher among non-Hispanic blacks (25.2%). Among those with at least one potential missed opportunity, Hispanics had the lowest proportion (85.2%) (Table 5).

Findings from this study demonstrate that among adults 18-64 years with high-risk conditions, influenza vaccination coverage was low overall as well as among those with multiple high-risk conditions. During the 2012-13 season, about 40-60% of adults 18-64 years at increased risk for influenza were unvaccinated against influenza. Vaccination coverage remained well below the previous Healthy People 2020 target of 90% for all the influenza high-risk groups studied and below the current target of 70% set for all adults (6).

Factors associated with lower influenza vaccination coverage among adults with high-risk conditions have been described in other studies and might include: lack of a preexisting relationship of state immunization programs with providers who serve adults at high risk; difficulty in implementing a risk-condition-based vaccination recommendation; persons with underlying health conditions not considering themselves as high risk limiting the effectiveness of targeted messages; and, historically low seasonal influenza vaccination coverage in this population (5, 7-11, 17).

Several ongoing programs or disease-related professional organizations have supported intensive efforts to improve influenza vaccination among persons with high-risk conditions (18-21). For example, the Diabetes Quality Improvement Project, a collaborative effort between public and private organizations to improve preventive care for persons with diabetes, including influenza vaccination, has been ongoing for more than 10 years (18, 19). The National Asthma Education and Prevention Program panel identified influenza vaccination as one of several “key clinical activities that should be considered as essential for quality asthma care” (20). The American Heart Association/American College of Cardiology together with other heart disease organizations recommended influenza vaccination as secondary prevention for cardiovascular disease (21). In addition, the Department of Health and Human Services (HHS) initiated a strategic framework to improve the health status of individuals with multiple chronic conditions (22-24). The HHS framework contains a vision statement, goals, objectives, and discrete strategies for individuals with multiple chronic conditions to guide the department in coordinating its efforts internally and externally through collaborating with stakeholders to improve care coordination, maximize the use of proven self-care management and other services, provide better tools and information to providers who deliver care to persons with multiple chronic conditions, and facilitate research to fill knowledge gaps and develop beneficial interventions. The framework outlines national strategies for improving health and quality of life for individuals with multiple chronic conditions, including maximizing use of proven services like vaccination (22-24). Those ongoing activities may help improve influenza vaccination coverage among persons with high-risk conditions.

As might be expected, this study found that vaccination coverage among persons 50-64 years was significantly higher than among those 18-49 years. This result remained after controlling for other demographic and access to care variables. As people age, the prevalence of high-risk conditions is likely to increase. In this study, the prevalence of lung disease, heart disease, and diabetes among adults 50-64 years were 10.8%, 13.8%, and 13.8%, respectively, compared with 6.3%, 4.6%, and 3.4%, respectively, among adults 18-49 years. Healthcare providers may be more likely to recommend influenza vaccination to persons 50-64 years with high-risk conditions because of a perception of greater risk for complications from influenza compared with younger persons 18-49 years (25). Healthcare providers should ensure that persons at high risk receive appropriate vaccinations regardless of age.

Influenza vaccination coverage also varied substantially among persons with specific high-risk conditions, ranging from 44.0% for adults with asthma to 62.5% for those with renal disease. Lower coverage for adults with asthma might reflect their concerns that the vaccine could trigger an asthma exacerbation making them less likely to be vaccinated, although studies found no evidence of asthma exacerbation or other severe side effects after influenza vaccination (26-28). Given that respiratory infections such as influenza can be serious in persons with asthma, the lower vaccination coverage in this risk group warrants further consideration (29). Offering influenza vaccination in the ER to those with asthma would be appropriate. Sometimes ERs may be the only place these patients interact with a medical provider (20). Physicians should consider each office or ER visit a potential opportunity to vaccinate persons with asthma (20).

We found that vaccination coverage among persons who have health insurance, have a regular physician for health care, and physician contacts in past 12 months were significantly associated with influenza vaccination. These findings remained after controlling for other variables and are consistent with other reports (8, 9, 30). Physician contact plays an important role in vaccination uptake (8, 9, 31). Having a regular physician and seeing a physician provide opportunities for education about influenza vaccination and offering vaccination and other prevention services. Persons with high-risk conditions may have more frequent contacts with their healthcare providers. Routine physician visits can provide important opportunities for providers to vaccinate persons with high-risk conditions.

There were missed opportunities for vaccinating adults with high-risk conditions. Although our findings suggest that recent physician contacts were independently associated with influenza vaccination, we also found a substantial proportion of individuals with high-risk conditions who had visited their physicians at least 10 times within the past year, but still were not vaccinated. Based on our study, overall, 90.1% of unvaccinated individuals reported at least one visit to a health care setting where vaccination could have been provided including 87.3% who had one or more physician contacts in the last 12 months, 15.2% who were hospitalized in the previous 12 months, and 31.7% who had visited an emergency room. In one study, a significant proportion of generalists and subspecialists failed to recommend influenza vaccination to their high-risk patients (17). Use of standing order programs might help reduce the number of missed opportunities for vaccinating persons who have already accessed the medical system (32-34). In addition, it is also important for subspecialists to recommend and offer influenza vaccination to high-risk adults. Although primary care physicians are the predominant providers for adults with chronic conditions in the health care system, subspecialists also see these patients with great frequency (35). However, one study indicated that about 22% of subspecialists did not stock the influenza vaccine. The most common factor in the decision to not stock vaccine was the perception that patients will receive the vaccine elsewhere (35). Subspecialists were less likely to stock and recommend influenza vaccine, especially cardiologists (35, 36). To reduce missed opportunities overall, subspecialists should be encouraged to vaccinate high-risk patients or refer their patients for vaccination (35, 35).

One limitation should be considered in interpreting these results. Information on influenza vaccination was self-reported and may be subject to recall bias. However, self-reported seasonal influenza vaccination status among older adults has been shown to have relatively high agreement with vaccination status ascertained from medical records (37-39).

Influenza vaccination coverage among adults with high-risk conditions remains suboptimal. In 2012-13, an estimated 40 million adults 18-64 years had underlying medical conditions, but only about 50% had received the vaccine and 90% of unvaccinated individuals may have missed at least one potential opportunity for receiving vaccination. Even though the influenza vaccination was expanded to include all persons ≥ 6 months of age in the 2010-11 season, the ACIP continued to emphasize that persons with high-risk conditions should be a focus of vaccination efforts (5). Substantial improvement in annual influenza vaccination of adults with high-risk conditions is needed to maximally reduce the health impact of influenza. Primary care providers, subspecialists, and pharmacists should routinely recommend and offer vaccinations when patients access the medical system (40). Expanded access through greater use of complimentary settings and vaccine providers, and better use of evidence-based practices at medical sites (e.g., standing orders, and reminder/recall notification) are important to improving influenza vaccination coverage further (33, 41).