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OffLine Summer 1998

Volume 12 Number 1

"Not immune to complacency." That headline in last month's USA Today alludes to the need to remain vigilant about childhood immunizations. A nationwide priority in recent years, childhood immunization rates have reached all-time highs in the United States. Scientists, however, are concerned that this success will lull policymakers and parents into a sense of complacency that will be disturbed only by drops in coverage or an outbreak of another epidemic. Of course, other factors can cause sub-optimal vaccination rates, including parental fears, misguided provider beliefs and uncoordinated patient tracking systems.

Group Health Center for Health Studies' Immunization Studies Program is doing its part to maintain a public vigilance toward both childhood and adult vaccinations by rigorously assessing coverage rates in a variety of situations and sub-populations, such as low birth weight babies. Documenting coverage problems is a first step toward implementing interventions designed to boost immunization adherence. In addition, the ISP and collaborators are laying the groundwork for a proposed HEDIS performance measure intended to increase pneumococcal vaccination rates among adults. This second issue of Off-Line dedicated to the ISP describes this research related to vaccination coverage, as well as that dealing with immunization effectiveness and infectious disease epidemiology.

Much of the ISP's original work concentrated on children. While this continues to be an important focus, investigators have more recently initiated research related to adult issues. Lisa Jackson and colleagues are collaborating with the Centers for Disease Control and Prevention (CDC) to develop a HEDIS performance measure to assess pneumococcal vaccination coverage in managed care organizations. Pneumococcal disease, responsible for 40,000 deaths annually, is the most common cause of vaccine-preventable disease deaths in the United States. The vaccine is estimated to be 60 percent effective in reducing hospitalization or death in the target population, defined as people over age 65 and adults under age 65 with chronic illnesses, such as cardiovascular disease. However, in 1994, only 30 percent and 15 percent of people in these 2 groups received the vaccination, far below the Healthy People 2000 goal of 60 percent coverage.

HEDIS was created to improve the quality of health care by standardizing the way in which health plans calculate and report information about performance. The challenge of including pneumococcal vaccination rates as a HEDIS outcome measure lies in calculating the appropriate numerator and denominator. Estimating the numerator, or the number of people receiving a pneumococcal vaccination, is complicated because they could have received the shot before enrolling in the HMO (it is usually a one-time shot). Thus, the HMO's automated immunization data would be incomplete for a substantial subset of the target population. Calculating the denominator, or the number of people eligible for the vaccination, is complicated by the fact that the target population is defined by age 65 or greater, which is straightforward, or, for those under 65, by the presence of chronic conditions, which is less so. That is, algorithms are needed to identify adult enrollees under age 65 with these conditions. According to Jackson, any final HEDIS performance measure will most likely rely on hybrid methodology using data from automated systems which are validated by chart review and/or member survey.

While not reaching the level of a HEDIS performance measure, guidelines at Group Health recommend screening all pregnant women for rubella and hepatitis B. Because a subset of women who receive prenatal care would not otherwise engage the health care system, pregnancy-related visits represent a unique opportunity to screen women at risk for vaccine-preventable diseases and to provide preventive care in appropriate instances. Compliance with these prenatal screening guidelines is not well documented, prompting Jackson to collaborate with the CDC to assess screening rates and whether appropriate steps are taken after delivery, if applicable.

The fact that rubella infection during pregnancy can lead to congenital malformations provides the rationale for prenatal screening. If a pregnant woman tests positive for rubella, the guidelines call for her to be immunized post-delivery before leaving the hospital. The health of the baby is the impetus behind the hepatitis B guideline. A woman who is a chronic carrier can transmit this blood-borne viral infection to her newborn infant. Perinatal transmission is largely preventable; however, if infants are born to women testing positive for hepatitis b are given immunoprophylaxis and an accelerated vaccination series beginning at birth, followed by blood testing. Effective implementation of both the rubella and hepatitis B guidelines requires systematic and centralized management and tracking systems. Improvement of these systems could be a goal of future interventions if Jackson and colleagues find less than optimal compliance with these prenatal screening guidelines.

Jackson recently worked with Group Health's Pregnancy Roadmap team to implement a new prenatal screening guideline for varicella, the chicken pox virus. Complications due to infection are much more common in adolescents and adults, providing incentive for implementing preventive measures in the older population.

The varicella vaccine was not available in the U.S. until 1995. Its relative recency raises interesting questions about its long-term effect on the epidemiology of chicken pox that could have implications for both children and adults. In a recent grant application, Jackson and ISP Research Associate Kari Bohlke proposed to address some of these issues, including changes in overall rates of the disease as well as shifts in relative distribution between age groups.

Pre-vaccine, chicken pox was essentially a universal childhood disease characterized by generally mild symptoms. In contrast, the rare adolescent or adult who contracted the disease often suffered far more serious complications. Post-vaccine, one possible scenario goes like this. The varicella vaccine causes drops in circulation of the chicken pox virus, meaning that susceptible persons (those not vaccinated, or not protected by the vaccination) will be less likely to be exposed to the disease during childhood. Consequently, the odds are increased that they will contract the disease later in life when the symptoms are much more serious. According to this possible scenario, the varicella vaccine may reduce the overall number of cases of chicken pox but increase the relative seriousness of the disease.

Jackson and Bohlke's grant application also builds on current ISP work examining the impact of the varicella vaccine on the epidemiology of herpes zoster. Commonly known as shingles, herpes zoster is a painful inflammation of the nerves caused by a reactivation of the chicken pox virus which may have lain dormant for decades. With symptoms that can span weeks or months and recur repeatedly, zoster is estimated to affect one-half of adults at some point in their lifetime. Preventing chicken pox in the first place should theoretically reduce rates of zoster. Among older people who have already had chicken pox, some experts speculate that immunity to zoster is boosted somewhat by exposure to the chicken pox virus circulating among the population. With the varicella vaccine causing a decrease in the ubiquity of the virus, it is possible that older people will be more prone to zoster after the vaccine's introduction. Alternatively, if this same group were vaccinated as adults, their immunity to zoster may actually increase.

Like herpes zoster, influenza viruses adversely impact a large segment of the population each year. While flu takes its biggest toll on the elderly and chronically ill, it accounts for substantial work absenteeism and health care visits among health, working adults. In an effort to identify an effective, easy-to-administer vaccine for use among this sub-group, Jackson and colleagues from 12 other sites across the U.S. tested a live, intranasal influenza vaccine against an intranasally-administered placebo.

Investigators found that while recipients of the live intranasal vaccine were just as likely to experience any flu-like illness relative to placebo recipients, they were less likely to experience serious influenza-like illness. Further, the live influenza vaccine reduced work absenteeism, health care use, use of prescription antibiotics and over-the-counter medications and illness days compared to placebo. The placebo and vaccine groups did not differ in the prevalence of serious adverse events, although vaccine-recipients were more likely to have a runny nose or sore throat in the week following vaccination. The investigators conclude that the intranasal vaccine was safe and effective among working , healthy adults.

Although the above study evaluated intranasally-administered influenza vaccine, injection is by far the more common form of administration. Another possible alternative to needles and syringes are jet injectors, compressed gas-powered appliances that "spray" the vaccine. This "spray" impacts more cells than does vaccine delivered via traditional injection, leading researchers to hypothesize that jet injectors could confer increased protection against influenza compared with needles. If jet injectors provide improved immunity over needles, a lower dose of vaccine could possibly be administered. This would be desirable given that the supply of influenza vaccine is limited.

Meanwhile on the child front, a number of surveys have shown that health care providers often delay immunization for low birth weight babies until they reach a certain weight (e.g., 10 pounds), even though vaccines are recommended at the same chronological age for premature infants as for those carried to term. Such delays are a concern because premature babies are particularly susceptible to vaccine-preventable diseases such as pertussis. Seeking to qualify this issue, ISP investigator Bob Davis and colleagues from 2 other HMOs recently conducted the first population-based study assessing immunization rates among low birth weight babies.

Investigators from the 3 HMOs examined rates of common childhood vaccinations from birth through 24 months for babies in 3 strata of birth weights: 1)less than 1500 grams; 2)1500–2500 grams; and 3)premature infants born at less than 38 weeks with birth weights exceeding 2500 grams. The specific vaccines examined were diphtheria-tetanus-pertussis (DTP), measles-mumps-rubella (MMR), oral polio (OPV) and haemophilus influenza type b(Hib). The investigators found that the lowest birthweight babies babies (LT 1500 grams) consistently had less up-to-date immunization status than did babies in the other two birth weight groups, but that the gap narrowed as the infants aged. That is, the biggest discrepancy between groups in immunization coverage existed in the first few months of life. At 2 years, the lowest birthweight babies had coverage rates of about 80 percent—rates approaching those of the general population but still significantly lower than those for the other 2 birthweight groups. The investigators suggest that outreach programs to physicians might help reduce this discrepancy. (This study was published in the August 11, 1999 edition of the Journal of the American Medical Association.)

Davis also spearheaded a study examining coverage levels of routinely recommended childhood vaccinations following implementation of change in the polio immunization schedule. Before 1997, most children received 4 doses of the polio vaccine in oral form (OPV). Because of adverse events associated with the initial 2 doses of OPV (at 2 and 4 months), experts recommended that the first 2 doses of vaccine be given by injection (IPV). This recommended schedule change meant that the number of injections for children aged 2 months would increase from three to four—IPV plus DTP, MMR, and Hib—which raised concerns that physicians or parents might be reluctant to subject children to 4 shots. Reassuringly, Davis and colleagues found that children who received IPV as their first polio vaccination were as likely to be up-to-date on their routine immunizations at age 12 months as children who received the OPV as their initial polio shot.

The last two issues of Off Line have described Group Health Center for Health Studies' extensive research program centered around immunizations. This work could not have been possible without the coordinated efforts of the Group Health clinic staff, the Immunization Clinical Roadmap Team (CRT), the Center for Health Promotion and the Committee on Prevention. In the face of downsizing and increasing workloads over the last several years, clinic staff have continued to make immunizations a priority by entering data and working a continually expanding immunization exception registry. Staff from CHP and CRT, particularly Roadmap Coordinator Angela Salazar, have overseen this work. In addition, the Committee on Prevention has provided oversight for policy development and consultation regarding implementation planning. The upshot is that Group Health is recognized as a national leader in this area, with some of the highest childhood immunization rates in the U.S. These Coop-wide efforts contribute greatly to the success of CHS' immunization research program.

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