2010–11 Influenza Prevention & Control Recommendations

Influenza Vaccination Coverage Levels

Continued annual monitoring is needed to determine the effects on vaccination coverage of vaccine supply delays and shortages, changes in influenza vaccination recommendations and target groups for vaccination, reimbursement rates for vaccine and vaccine administration, and other factors. One of the Healthy People 2010 objectives (objective no. 14–29a) includes achieving an influenza vaccination coverage level of 90% for persons aged 65 years and older and among nursing home residents; new strategies to improve coverage are needed to achieve this objective.

On the basis of 2009 final data and 2010 early release data from the National Health Interview Survey (NHIS), estimated national influenza vaccine coverage during the 2007–08 and 2008–09 influenza seasons did not increase substantially among persons aged 65 and older years and those aged 50–64 years (Table 3) and are only slightly higher than coverage levels observed before the 2004–05 vaccine shortage year. In the 2007–08 and 2008–09 influenza seasons, estimated vaccination coverage levels (based on NHIS data) among adults with high–risk conditions aged 18–49 years were 30.4% and 33%, respectively, substantially lower than the People 2000 and Healthy People 2010 objectives of 60%  (Table 3). Among adults with asthma aged 18–49 years and 50–64 years, estimated coverage during the 2006–07 influenza season was 24% and 55% respectively; the national objective for coverage among adults with asthma is 60%. Epidemiologic studies conducted during the 2009 pandemic indicated that more hospitalizations and deaths were occurring among adults aged younger than 65 years with high–risk conditions than among any other group, and these adults were among the initial target groups to receive the 2009 H1N1 vaccination while vaccine supply was limited. However, coverage among adults aged younger than 65 years with medical conditions that confer a higher risk for influenza complications was less than 40% for the 2009 H1N1 monovalent vaccine.

During the 2009 influenza A (H1N1) pandemic, state–level estimates of seasonal vaccine coverage data for both seasonal influenza and the monovalent 2009 H1N1 vaccines were obtained via telephone surveys conducted by the Behavioral Risk Factor Surveillance System (BRFSS) and the National 2009 H1N1 Flu Survey. By January 31, 2010 estimated state seasonal influenza vaccination coverage among persons aged 6 months and older ranged from 30.3% to 54.5% (median: 40.6%). Median coverage was 41.2% for children aged 6 months–17 years, 38.3% for adults aged 18–49 years with high–risk conditions, 28.8% for adults aged 18–49 years without high–risk conditions, 45.5% for adults aged 50–64 years, and 69.3% for adults aged 65 years and older. These results, compared with the previous season, suggest large increases in coverage for children and a moderate increase for adults aged 18–49 years without high–risk compared with seasonal influenza vaccine coverage estimates in previous seasons. However, vaccine coverage estimates using BRFSS data typically have been higher than estimates derived from NHIS data.

Studies conducted among children and adults indicate that opportunities to vaccinate persons at risk for influenza complications (e.g., during hospitalizations for other causes) often are missed. In one study, 23% of children hospitalized with influenza and a comorbidity had a previous hospitalization during the preceding influenza vaccination season. In a study of hospitalized Medicare patients, only 31.6% were vaccinated before admission, 1.9% during admission, and 10.6% after admission. A study in New York City conducted during 2001–2005 among 7,063 children aged 6–23 months indicated that 2–dose vaccine coverage increased from 1.6% to 23.7% over time; however, although the average number of medical visits during which an opportunity to be vaccinated decreased during the course of the study from 2.9 to 2.0 per child, 55% of all visits during the final year of the study still represented a missed vaccination opportunity. Using standing orders in hospitals increases vaccination rates among hospitalized persons, and vaccination of hospitalized patients is safe and stimulates an appropriate immune response. In one survey, the strongest predictor of receiving vaccination was the survey respondent"e;s belief that he or she was in a high–risk group, based on data from one survey; however, many persons in high–risk groups did not know that they were in a group recommended for vaccination. In one study, over half of adults who did not receive influenza vaccination reported that they would have received vaccine if this had been recommended by their health–care provider.

Reducing racial/ethnic health disparities, including disparities in influenza vaccination coverage, is an overarching national goal that is not being met. Estimated vaccination coverage levels in 2008 among persons aged 65 years and older were 70% for non–Hispanic whites, 52% for non–Hispanic blacks, and 52% for Hispanics. Among Medicare beneficiaries, other key factors that contribute to disparities in coverage include variations in the propensity of patients to actively seek vaccination and variations in the likelihood that providers recommend vaccination. One study estimated that eliminating these disparities in vaccination coverage would have an impact on mortality similar to the impact of eliminating deaths attributable to kidney disease among blacks or liver disease among Hispanics. Differences in coverage by race or ethnicity might be partly attributable to differences in beliefs about vaccine effectiveness and safety. Among nursing home patients, fewer blacks and Hispanics are offered vaccine or receive it compared with whites, and blacks refuse vaccination more frequently. Disparities in seasonal influenza vaccine coverage among adult whites (43%), blacks (31%), and Hispanics (31%) also were observed during 2009–2010.

Reported vaccination levels are low among children at increased risk for influenza complications. Coverage among children aged 2–17 years with asthma was estimated to be 29% for the 2004–05 influenza season. During the 2007–08 influenza season, the fourth season for which ACIP recommended that all children aged 6–23 months receive vaccination, National Immunization Survey data demonstrated that 41% of children aged 6–23 months received at least 1 dose of influenza vaccine, and 23% were fully vaccinated (i.e., received 1 or 2 doses depending on previous vaccination history); however, results varied substantially among states. Data from the eight Immunization Information System sentinel sites during 2008–09 indicated that 48% of children aged 6–23 months had received at least 1 dose, and 29% were fully vaccinated. Coverage levels in these sites for older children were lower and declined with increasing age, ranging from 22% fully vaccinated among children aged 2–4 years to 9% among children aged 13–18 years. As has been reported for older adults, a physician recommendation for vaccination and the perception that having a child be vaccinated "is a smart idea" were associated positively with likelihood of vaccination of children aged 6–23 months. Similarly, children with asthma were more likely to be vaccinated if their parents recalled a physician recommendation to be vaccinated or believed that the vaccine worked well. Implementation of a reminder/recall system in a pediatric clinic increased the percentage of children with asthma receiving vaccination from 5% to 32%. Reminder/recall systems might be particularly useful when limited vaccine availability requires targeted vaccination of children with high–risk conditions.

Although annual vaccination is recommended for HCP and is a high priority for reducing morbidity associated with influenza in health–care settings and for expanding influenza vaccine use, NHIS data demonstrated a vaccination coverage level of only 44.4% among HCP during the 2006–07 season, and 49% during the 2007–08 season (Table 3). Coverage levels during the 2009 pandemic were higher for seasonal vaccine, but remained low for the 2009 pandemic vaccine. By mid–January 2010, estimated vaccination coverage among HCP was 37% for 2009 pandemic influenza A (H1N1) and 62% for seasonal influenza, based on a RAND Corporation–conducted telephone survey that used a somewhat different methodology than NHIS. Overall, 64% received either of these influenza vaccines, higher coverage than any previous season, but only 35% of HCP reported receiving both vaccines. Vaccination of HCP has been associated with reduced work absenteeism and with fewer deaths among nursing home patients and elderly hospitalized patients. Factors associated with a higher rate of influenza vaccination among HCP include older age, being a hospital employee, having employer–provided health–care insurance, having had pneumococcal or hepatitis B vaccination in the past, or having visited a health–care professional during the preceding year. HCP who decline vaccination frequently express doubts about the risk for influenza and the need for vaccination, are concerned about vaccine effectiveness and side effects, and dislike injections.

Vaccine coverage among pregnant women increased during the 2007–08 influenza season, with 24% of pregnant women reporting vaccination, excluding pregnant women who reported diabetes, heart disease, lung disease, and other selected high–risk conditions; seasonal vaccine coverage estimates for 2008–09 were only 11%, however, which is closer to pre–2007 estimates and likely reflects variation in estimates caused by the small sample size rather than significant fluctuations in coverage (Table 3). The causes of persistent low coverage among pregnant women are not fully determined. However, in a study of influenza vaccination acceptance by pregnant women, 71% of those who were offered the vaccine chose to be vaccinated. However, a 1999 survey of obstetricians and gynecologists determined that only 39% administered influenza vaccine to obstetric patients in their practices, although 86% agreed that pregnant women"e;s risk for influenza–related morbidity and mortality increases during the last two trimesters. Pregnancy was an important risk factor during the 2009 H1N1 pandemic, and because the 2009 H1N1 influenza virus is expected to continue circulation during 2010–11, improved vaccination coverage among pregnant women is needed.

Influenza vaccination coverage in all groups recommended for vaccination remains suboptimal. Despite the timing of the peak of influenza disease, administration of vaccine decreases substantially after November. According to results from NHIS, for the three most recent influenza seasons for which these data are available, approximately 84% of all influenza vaccinations were administered during September–November. Among persons aged 65 years and older, the percentage of September–November vaccinations was 92%. Because many persons recommended for vaccination remain unvaccinated at the end of November, CDC encourages public health partners and health–care providers to conduct vaccination clinics and other activities that promote seasonal influenza vaccination annually during National Influenza Vaccination Week (December 6–12, 2010) and throughout the remainder of the influenza season.

Self–report of influenza vaccination among adults compared with determining vaccination status from the medical record, is a sensitive and specific source of information. Patient self–reports should be accepted as evidence of influenza vaccination in clinical practice. However, information on the validity of parents"e; reports of pediatric influenza vaccination is not yet available.

Vaccination coverage estimates for the influenza A (H1N1) 2009 monovalent vaccines indicate that most doses were administered to the initial target groups, and that, by January 2, 2010 (approximately 90 days after vaccine first became available), an estimated 20% of the U.S. population (61 million persons) had been vaccinated, including 28% of persons in the initial target groups. An estimated 30% of U.S. children aged 6 months–18 years had been vaccinated, including 33% of children aged 6 months–4 years. Estimated coverage for specific initial target groups was 38% for pregnant women, 22% for HCP, and 12% for adults aged 25–64 years with medical conditions that confer a higher risk for influenza complications. Estimates of 2009 H1N1 vaccination coverage levels generally were higher among non–Hispanic whites than among non–Hispanic blacks. These coverage estimates were in the same approximate range as estimates for seasonal vaccination coverage, suggesting that concerns about the pandemic were not sufficient to overcome some barriers to influenza vaccination among persons at higher risk for influenza complications.

TABLE 3. Influenza vaccination* coverage levels for the 2006–07, 2007–08, and 2008–09 influenza seasons, among population groups — National Health Interview Survey (NHIS), United States, 2007–2009, and National Immunization Survey (NIS), 2006–2008.