Factors influencing immunization rates

Measles (shown) can be prevented by a combination vaccine.
Measles (shown) can be prevented by a combination vaccine.
  • There is a direct correlation between the rates of infant immunization in a community and the rates of vaccine-preventable diseases.
  • The complexity of the immunization schedule has posed challenges for both families and providers.
  • Missed opportunities present a significant barrier to adequate immunization by the age of 2 years.
  • The personal and philosophical beliefs of the parents are the most influential in the vaccination decision.

Immunization programs have had a dramatic impact on reducing the number and severity of communicable disease outbreaks. Such diseases as smallpox and polio have been completely eradicated in the United States. However, many other vaccine-preventable diseases persist and in some cases have increased in prevalence because of lowered immunity in the general population. Childhood vaccines do much to provide lifetime immunity to certain diseases, but for other diseases, such as pertussis, additional doses of vaccine are now recommended to protect individuals with waning immunity.1 Experience has taught us that there is a direct correlation between the rates of infant immunization in a community and the rates of vaccine-preventable diseases.

A national goal of Healthy People 2010 is to “achieve and maintain effective vaccination coverage levels for universally recommended vaccines among young children.”2 The specific goal is for 90% of all children to have completed the recommended series of immunizations by age 2 years. Vaccination rates of 90% are generally sufficient to prevent the spread of communicable disease via “herd immunity.”

Herd immunity is conferred when most of the individuals within a community have developed immunity either from receiving a vaccination against a particular disease or from having contracted the disease. In communities with herd immunity, vulnerable individuals are protected because the majority of persons with whom they come into contact are immune to and incapable of spreading the disease. Effective vaccination programs are important in raising the levels of herd immunity in communities.

Unfortunately, as we near the target year 2010, studies reveal that we as a nation are falling short of this important goal. Nurse practitioners and physician assistants have a unique opportunity to assure immunization adequacy in their patients. Many people may be unaware of the vaccine recommendations for their age group or may not have had access to vaccine services or information. In addition, adult patients and parents of young children may have difficulty making sense of the conflicting stories about vaccine safety. To reach the goal of providing herd immunity in communities requires diligence in using each and every patient encounter as an opportunity to determine vaccination status.3

A number of factors have been identified as impacting immunization rates in the United States. Kimmel et al have categorized these barriers as systems barriers, provider barriers, and parent or patient barriers.4

Systems barriers

Barriers to immunization that involve health-care organizations and economics are considered systems barriers. Some of the factors that impact national immunization rates include incomplete use of a centralized vaccine registry, lack of a universal vaccination record, vaccine shortages, vaccine costs, and complexity of the immunization schedule.

Centralized vaccination registries: Immunization information systems (IIS) or immunization registries have been federally funded in the United States since 1994.5,6 For the health-care provider, an IIS can be a complete record of the vaccines previously received by a patient, not just through a specific practice but from all other sources, including health department clinics and other providers. That information can assist the PA or NP in determining if vaccines should be offered while the individual is in the office. This can reduce missed opportunities for administering vaccines during nontraditional visits, such as a “sick” or urgent-care appointment, and avoid the need to reschedule an appointment to receive vaccines.

IIS can also benefit patients and parents by providing an accurate, accessible vaccine record. Many individuals are unsure about when a vaccine was last given, the type of vaccine received, and when additional vaccines are needed.

Most states have a centralized vaccine registry system in place, but a number of factors can interfere with its effective utilization. For example, the value of an IIS is limited by the number of providers who regularly and accurately upload vaccination information into the system. Subsequently, shortages in office staff may cause delays in information retrieval. When an accurate, up-to-date record is unavailable, patients can receive duplicate, invalid, or mistimed vaccine doses, or they can miss needed vaccines altogether. Many state registries record only vaccines given to children and may not store information on adults.

Vaccine shortages: Limited amounts of vaccine are another systems barrier that can impact vaccination rates. Reasons for vaccine shortages include dwindling numbers of manufacturers, delays caused by the manufacturing process, and situations in which demand exceeds supply.

The number of licensed vaccine manufacturers in the United States continues to decrease as many companies choose to develop more lucrative vaccines or move their operations overseas. A number of manufacturers have ceased production of some or all vaccines because of their lack of profitability or the high costs associated with vaccine liability.

When vaccines have only a single manufacturer, that manufacturer may from time to time struggle to keep up with demand and shortages can develop. Shortages can also be precipitated by changes in vaccine requirements, e.g., to include an additional age cohort that needs to receive the vaccine. In addition, newer vaccines may gain popularity very quickly, and the supply may be depleted before additional vaccine can be manufactured. In 2001, eight of the 11 universal childhood vaccines were either unavailable or in short supply.7

Several vaccines for adults have also been in short supply, such as the combined tetanus, diphtheria, and pertussis (Tdap) vaccine and the herpes zoster, or shingles, vaccine. When vaccines are unavailable, patients may reschedule their appointment to receive the missing vaccines or they may delay receiving any vaccines until the entire series is available. In many cases, individuals either fall behind or forget to return once the vaccines are available.

Socioeconomic factors have been a primary concern in assuring that all children have access to vaccines. The rates of uninsured children are at historic highs. Even when families are covered by an insurance program, deductibles or co-pays may be very high or coverage for vaccines may be incomplete. National programs, such as Vaccines for Children (VFC), provide vaccines for uninsured or underinsured children, but few programs provide free vaccines to adults.

Appointments for well-child examinations are a traditional time for vaccine administration during the first two years of life. Some families exceed the allowance for well-child care or immunizations before completing all the recommended visits or vaccines. This may result in families' postponing vaccines because of cost. Older children and adults are less likely to receive well-care examinations and may not see a primary-care provider for years except for acute-care or urgent-care visits. Unless the NP or PA asks about vaccine status at these visits, individuals may not receive needed vaccines.

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