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 related to vaccination coverage among adults and children. National health objectives for 2010 include achieving an influenza vaccination coverage level of 90% for persons aged >65 years and among nursing home residents (279,280), but new strategies to improve coverage are needed to achieve these objectives (281-282). Increasing vaccination coverage among persons who have high-risk conditions and are aged <65 years, including children at high risk, is the highest priority for expanding influenza vaccine use.

On the basis of preliminary data from the National Health Interview Survey (NHIS), estimated national influenza vaccine coverage in the second quarter of 2006 among persons aged >65 years and 50-64 years was 66% and 32%, respectively (283). Compared with coverage estimates from the 2005 NHIS, coverage in these age groups has increased (Table 5) (283). In early October 2004, one of the influenza vaccine manufacturers licensed in the United States announced that it would be unable to supply any vaccine to the United States, causing an abrupt and substantial decline in vaccine availability and prompting ACIP to recommend that vaccination efforts target certain groups at higher risk for influenza complications. The inability of this manufacturer to produce vaccine for the United States reduced by almost one half the expected supply of TIV available for the 2004-05 influenza season (284,285). Although vaccine supply was adequate for the 2005-06 influenza season, recent trends in vaccination coverage are difficult to interpret until analyses of recent NHIS vaccination coverage data are completed.

During 1989-1999, influenza vaccination levels among persons aged >65 years increased from 33% to 66% (286,287), surpassing the Healthy People 2000 objective of 60% (281). Possible reasons for increases in influenza vaccination levels among persons aged >65 years include 1) greater acceptance of preventive medical services by practitioners; 2) increased delivery and administration of vaccine by health-care providers and sources other than physicians; 3) new information regarding influenza vaccine effectiveness, cost-effectiveness, and safety; and 4) initiation of Medicare reimbursement for influenza vaccination in 1993 (129,160,166,167,288,289). However, since 1997, increases in influenza vaccination coverage levels among the elderly have slowed markedly, with coverage estimates during years without vaccine shortages since 1997 ranging between 63% and 66%.

In 2004, estimated vaccination coverage levels among adults with high-risk conditions aged 18-49 years and 50-64 years were 26% and 46%, respectively, substantially lower than the Healthy People 2000 and Healthy People 2010 objectives of 60% (Table 5) (279,280). In 2005, vaccination coverage among persons in these groups decreased to 18% and 34%, respectively; vaccine shortages during the previous influenza season likely contributed to these declines in coverage.

Opportunities to vaccinate persons at risk for influenza complications (e.g., during hospitalizations for other causes) often are missed. In a study of hospitalized Medicare patients, only 31.6% were vaccinated before admission, 1.9% during admission, and 10.6% after admission (290). A study conducted in New York City during 2001-2005 among 7,063 children aged 6-23 months determined that 2-dose vaccine coverage increased from 1.6% to 23.7%. 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 (291). Using standing orders in hospitals increases vaccination rates among hospitalized persons (292). In one survey, the strongest predictor of receiving vaccination was the survey respondent's belief that he or she was in a high-risk group. However, many persons in high-risk groups did not know that they were in a group recommended for vaccination (293).

Reducing racial and ethnic health disparities, including disparities in influenza vaccination coverage, is an overarching national goal that is not being met (279). Although estimated influenza vaccination coverage for the 1999-00 season reached the highest levels recorded among older black, Hispanic, and white populations, vaccination levels among blacks and Hispanics continue to lag behind those among whites (287,294). Estimated vaccination coverage levels in 2005 among persons aged >65 years were 68% for non-Hispanic whites, 47% for non-Hispanic blacks, and 49% for Hispanics (283). Among Medicare beneficiaries, unequal access to care might not be the only factor in contributing toward disparity levels; other key factors include having patients that actively seek vaccination and providers that recommend vaccination (295,296). 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 (297).

Reported vaccination levels are low among children at increased risk for influenza complications. Coverage among children aged 2-17 years with asthma for the 2004-05 influenza season was estimated to be 29% (298). One study reported 79% vaccination coverage among children attending a cystic fibrosis treatment center (299). During the first season for which ACIP recommended that all children aged 6 months-23 months receive vaccination, 33% received >1 dose of influenza vaccination, and 18% received 2 doses if they were unvaccinated previously (300). Among children enrolled in HMOs who had received a first dose during 2001-2004, second dose coverage varied from 29% to 44% among children aged 6-23 months and from 12% to 24% among children aged 2-8 years (301). A rapid analysis of influenza vaccination coverage levels among members of an HMO in Northern California demonstrated that during 2004-2005, the first year of the recommendation for vaccination of children aged 6-23 months, 1-dose coverage was 57% (302). Data collected in February 2005 indicated a national estimate of 48% vaccination coverage for >1 doses among children aged 6-23 months and 35% coverage among children aged 2-17 years who had one or more high-risk medical conditions during the 2004-05 season (303). 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 (304). 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 (305). Implementation of a reminder/recall system in a pediatric clinic increased the percentage of children with asthma or reactive airways disease receiving vaccination from 5% to 32% (306).

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 (307-309), national survey data demonstrated a vaccination coverage level of only 42% among HCP (CDC, unpublished data, 2006). Vaccination of HCP has been associated with reduced work absenteeism (251) and with fewer deaths among nursing home patients (257,258) and elderly hospitalized patients (260). 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 previous year. Non-Hispanic black HCP were less likely than non-Hispanic white HCP to be vaccinated (310).

Limited information is available regarding influenza vaccine coverage among pregnant women. In a national survey conducted during 2001 among women aged 18-44 years without diabetes, those who were pregnant were significantly less likely to report influenza vaccination during the previous 12 months (13.7%) than those women who were not pregnant (16.8%) (311). Only 16% of pregnant women participating in the 2005 NHIS reported vaccination, excluding pregnant women who reported diabetes, heart disease, lung disease, and other selected high-risk conditions (CDC, unpublished data, 2006) (Table 5). In a study of influenza vaccine acceptance by pregnant women, 71% of those who were offered the vaccine chose to be vaccinated (312). 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's risk for influenza-related morbidity and mortality increases during the last two trimesters (313).

Data indicate that self-report of influenza vaccination among adults, compared with determining vaccination status from the medical record, is both a sensitive and specific source of information (314). Patient self-reports should be accepted as evidence of influenza vaccination in clinical practice (314). However, information on the validity of parents' reports of pediatric influenza vaccination is not yet available.

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