Childhood Immunizations: A Model for Preventive Health

Because prevention is rarely addressed in medical training, many medical students never systematically learn how to practice preventive medicine. As a result, effective preventive measures such as the routine immunization of children and adults are sometimes overlooked in day-to-day clinical practice despite overwhelming evidence of their utility.

• Who has not been immunized?
• Why don't doctors vaccinate all appropriate patients?
• Can public interventions raise immunization levels?
• How can medical students address underimmunization?

Immunization of both the very young and the elderly is one of the most effective ways to contain morbidity and mortality from infectious disease. Despite low cost and widespread availability of vaccines, however, outbreaks of vaccine-preventable diseases continue to occur. This was illustrated dramatically during the measles epidemic of 1989-1991, when 55,000 cases of measles were reported. According to the National Vaccine Advisory Committee, low immunization rates in many communities, particularly among individuals under two years of age, were the primary cause of the outbreaks.1

In response to outbreaks and reports of low immunization levels, public and primary health care providers intensified efforts to deliver vaccines to preschool children who were not receiving vaccines on time. In 1989, a two-dose measles vaccine schedule was instituted. Grass-roots organizations recruited children for enrollment in preventive and well-child services. Immunization rates began to rise; in 1996, 78% of 2-year-olds received a full series of childhood immunizations on time (see Figure 1). Correspondingly, the number of measles cases declined from a peak of 27,000 in 1989 to 433 seven years later.2 However, new outbreaks of diseases continue to occur. Morbidity statistics show recent increases in cases of whooping cough, a disease that can be prevented by pertussis vaccine. Among adults, particularly the elderly, influenza and pneumococcal disease continue unabated (see Figure 2).

Morbidity and mortality from preventable diseases will continue until all eligible individuals are appropriately immunized. Medical students are in a position to promote universal vaccination and deliver effective, preventive health care through intervention at many levels. Many public health inadequacies can be addressed through legislative and local advocacy. Barriers to immunization within communities may be assessed and changes implemented through outreach activities. Most importantly, students can begin an educational dialogue in preventive health among peers and faculty, with the aim of administering immunizations to all appropriate children and adults.

STUDENT ORGANIZERS GUIDE

Suggested Activities

• Educate yourself and your peers! This Project-in-a-Box examines the status of childhood and adult immunizations within the last few years and suggests how medical student can become involved in the delivery of immunization services. Ideas include giving a presentation to peers and faculty during primary care ward rotations, distributing fact cards on immunizations for students and residents to carry in their white coats, and organizing a panel discussion about public health and immunization delivery.
• Activate your community! Form an alliance with your local health department to learn where local deficits exist in immunizing children and adults. Assist public clinics in following up on children who have fallen behind on immunizations. Promote adult immunization by visiting nursing homes and passing out flyers at colleges and shopping malls.

Figure 1. Immunization Rates: What 78% Actually Means
In 1996, 78% of two-year-olds in America had received the primary immunization series recommended by the American Academy of Pediatrics, the American Association of Family Practitioners and the Advisory Committee on Immunization Practices. This series includes four doses of diphtheria, tetanus and pertussis (DTP) vaccine; three doses of polio virus vaccine, which is either live (OPV) or inactivated (IPV); one dose of measles, mumps and rubella (MMR) vaccine; and three doses of Haemophilus influenzae b (Hib) vaccine.2 Hepatitis and varicella immunization levels are not included in this figure.

• The immunization rate is determined by a Centers for Disease Control and Prevention (CDC) audit of hundreds of thousands of clinic records.
• Immunization rates may predict disease incidence. In one study, a population with 50% of children immunized against measles experienced 11.6 cases of measles per 1000 people. A population with 80% of children immunized against measles experienced no cases of measles.24 "Coverage of 80% or less may be sufficient to prevent sustained measles outbreaks in an urban community," wrote the study authors. However, little supporting data exists. Few studies have looked at how specific immunization rates correlate with incidence of disease.
• Incidence of preventable diseases is just as important as immunization rates for assessing child health in America.

Underimmunization in America: A Problem of Access to Care
Underlying problems of access to immunizations is the question of who will pay for services rendered. In 1982, it cost $6.69 to fully immunize a child in the public sector. Ten years later, the cost for recommended immunizations was $128.79 in the public sector and $243.90 in the private sector.3 New additions to the vaccine schedule, such as the Haemophilus influenzae b and Hepatitis B vaccines, a second dose of the measles, mumps, and rubella (MMR) vaccine, as well as the addition of a federal excise tax, pushed up the price drastically. Rising costs presented a clear stumbling block to uninsured and underinsured children, many of whom lived near the poverty level and could not afford to pay for vaccines. Questions about vaccine safety arose and skyrocketing liability added to operating costs for providers and vaccine manufacturers. Vaccine development and manufacturing was threatened as pharmaceutical companies faced reduction of the relatively low profit margin offered by the vaccine market; many companies stopped manufacturing vaccines altogether. In an attempt to preserve vaccine affordability and persuade pharmaceutical companies not to abandon production of vaccines, Congress passed the National Childhood Vaccine Injury Compensation Act in 1986. This act protected providers and pharmaceutical companies from some lawsuits, compensated families of injured children, and designated a vaccine excise tax to fund these activities.

Outbreaks of measles in the late 1980s demonstrated that immunization services were not being utilized by some children. Between 1989 and 1991, there were 55,000 cases, 11,000 hospitalizations and 130 deaths related to measles.4 Poverty played a large role in these outbreaks. During the 1980s, enrollment in Medicaid and Aid to Families with Dependent Children (AFDC) began declining5; as a result, many AFDC children went unimmunized. Social factors associated with poverty also had a hand in reduced health care availability. Parents sometimes doubted the benefit of medical care in preventing disease.6 Family characteristics such as race, family size and maternal education were associated with reduced access to immunizations7 as were logistical concerns such as lack of transportation and child care. Inability to pay for care also directly affected health care services; in one study, pediatricians in Washington state were more likely to refer children to the public health sector for immunizations when cost was perceived as an issue.8 This meant a break in continuity of care for children who already faced numerous other health-related disadvantages.

One of the outstanding problems with this system of health care was the failure to establish a medical home, most significantly for children living in poverty. In a medical home, the child is followed by a provider who knows the child's medical history and has established a relationship with the child's family. A medical home provides ongoing health care, which includes preventive services like screening for lead poisoning and anemia, as well as administration of immunizations.

Recent studies suggest that private offices make better medical homes than public health clinics. Public clinics often have poor continuity of care characterized by delays between immunizations, more missed appointments and increased missed opportunities when compared with private practices.9 A missed opportunity occurs when a child eligible for an immunization is seen by a health care provider but is not immunized. Children of low socioeconomic status followed in private settings had higher immunization rates than similar children seen in public clinics.10

At President Clinton's urging, Congress passed the Vaccines for Children bill (VFC) in 1994, and federally purchased vaccines for all Medicaid-enrolled, underinsured and uninsured children became available in private as well as public clinics. Providers in 48 states now receive vaccines directly from the manufacturer or the local health department; the remaining two states plan to begin shipping vaccines to providers soon. In one study, VFC vaccines reduced the number of missed opportunities among physicians; providers using VFC vaccines were eight times more likely to offer immunizations to their patients.11 More importantly, VFC vaccines appear to help children to establish a medical home, as 70% of the provider sites are in the private sector.11

Health care providers play perhaps the most crucial role in underimmunization of children. Recent literature suggests that "many -- if not most -- undervaccinated patients are seen an adequate number of times in physicians' offices."12 Missed opportunities to vaccinate often occur when a physician decides against immunization based on a medically invalid reason. Common reasons that vaccination is incorrectly postponed include upper respiratory infections, gastroenteritis and resolving minor illness. Missed opportunities in a study in Baltimore, Maryland, occurred in one-third of office visits.13 If all immunizations had been appropriately administered in this setting, 73% of children would have been fully immunized by age two. In actuality, only 55% of these patients were up-to-date on immunizations.

There are very few reasons to withhold immunizations; these include anaphylactic reactions to certain antibiotics and previous doses of vaccines, or encephalopathy following vaccine administration. (See Figure 4.) Failure to screen immunization records also results in missed opportunities. Parental recall is an ineffective method of screening for missed immunizations; only 27% of parents in a 1994 study were able to correctly identify whether their child was due for immunizations.14 Doctors' own estimates of immunization rates in their practices tend to be overly optimistic; one study found that on average, doctors overestimated their immunization rates by 10%,15 suggesting that physicians may not be aware of which patients are due for immunizations. Another cause of missed opportunities is failure to administer all recommended vaccines simultaneously.16

Physical administration of vaccines is not the only way that physicians contribute to the public health. They are vital to enrolling patients in a system of care that educates parents on well-child issues and recalls patients to the office when they fall behind on preventive measures, including immunizations. Surveillance, which involves recognizing and reporting infectious diseases to the local health department, is difficult without providers. Furthermore, providers can improve their own services and reduce missed opportunities through consultation with the CDC.

Fragmentation of health care delivery into the public health structure and individual provider units underlies many of the problems of childhood underimmunization. Providers often are independent actors who lack good communication channels with the public health system. This two-way communication is absolutely essential to maintain the public's health. Government agencies like the CDC and state and local health departments collect and interpret enormous amounts of data to determine who needs augmented health services. In turn, health officials plan interventions to interfere with disease outbreaks and raise immunization levels. Implementing interventions is impossible without the participation of health care providers. Thus, frequent interaction between individuals in private practice and public health departments is required for maintenance and upkeep of the public health.

Figure 2. Adult Immunization: A Long-Neglected Prevention Tool
Adult immunizations have recently begun attracting attention. Little is known about who is at risk for underimmunization, what role providers play in undervaccination, and if interventions in private offices and at the public health level can boost immunization levels.

Barriers to adult immunization are reminiscent of barriers children have faced in accessing vaccines over the past 15 years:

• Providers often miss opportunities to vaccinate, especially at hospital admission and discharge. Missed opportunities to vaccinate hospitalized adults occurred 80% of the time with pneumococcal vaccine and 65% of the time with influenza vaccine.25
• Public and private insurers reimburse inadequately.
• Federal support for vaccine delivery is lacking.26
• Influenza (the Flu): Causes an estimated 4 million excess respiratory illnesses per year. Immunization rate in 1995 was 58%.27
• Pneumococcus: Most common cause of bacterial pneumonia requiring hospitalization, accounts for an estimated 40,000 deaths per year. Immunization rate in 1995 was 36%.27
• The greatest risk for morbidity and mortality from influenza and pneumococcus occurs in patients older than age 65, so all of these individuals should be appropriately vaccinated!

Removing Obstacles to Preventive Care
Intervention occurs in the public health arena as well as in the offices of private practitioners. Public health interventions include formulation of immunization goals, standards, entitlements and providers' education and assessment. In 1991, the National Vaccine Advisory Committee (NVAC) published 18 standards for immunization services, calling for low cost, readily available vaccines, and instruction for physicians on how to ensure delivery of quality services to patients.1 (See Figure 5 and The Measles Epidemic: Problems, Barriers and Recommendations, appendix.) The Childhood Immunization Initiative, passed in 1993, outlined six goals to improve immunization services at a public health level. These goals include: 1) improving quality and quantity of vaccine-delivery services, 2) increasing community participation and education, 3) reducing vaccine cost for parents, 4) improving surveillance for immunization levels and disease outbreaks, 5) forming and strengthening public-private partnerships and 6) improving vaccines.17

Entitlements, which are government payments to individuals and organizations, fund some of these goals. The most prominent public entitlement for childhood immunizations is VFC, which purchases vaccines for Medicaid-enrolled, underinsured and uninsured individuals. As of 1995, 14 states also had universal purchase programs that purchase vaccines for all children within a state. Like VFC, universal purchase reduces costs for families and providers, reduces missed opportunities, and encourages establishment of a medical home.

When implemented in private settings, publicly formulated interventions have impressive results. In Georgia, the CDC assessed immunization rates and gave feedback on immunization practices to physicians during a six-year period. This effort resulted in an increase from 53% to 89% of children immunized at age two.18 Employment of the NVAC's Standards, formulated in response to the measles outbreaks (see Figure 5), resulted in a 40% improvement in immunization rates.19 Linking the receipt of immunizations with Women, Infant and Children (WIC) voucher provision also resulted in a fivefold increase in immunizations administered.20 The potential for WIC to affect unvaccinated children is enormous, as WIC reaches 44% of the nation's birth cohort, many of whom live near the poverty level and are at risk for undervaccination.

Community coalitions play an enormous role in publicizing immunizations and tracking down children to be vaccinated. In coordination with health departments, community coalitions tailor their services to areas of greatest need locally. The Shots by Two Program in Florida opened a "fast track" immunization clinic. Volunteers "adopt" newborns and send a congratulatory card to the parents, a first birthday card and appropriate immunization materials.21 In Alexandria, Virginia, the local hospital and the health department wrote a plan to immunize all children. Community-outreach activities include bookmarks, health fairs, library presentations and clinics in churches.

Figure 3. Quick vaccine facts for medical students on the wards

• Lapsed immunizations: If a child has fallen behind on shots, immunization should occur on the next visit as if the usual interval had elapsed.
• Unknown immunization status: For unknown immunization status, the series should be started over.
• Dosages: All children, including low birthweight and premature infants, should receive full doses of vaccines.

Common side effects:

• DTP--Fever, local irritation in first 48 hrs.
• MMR--Fever and rash 7-10 days later
• Killed vaccines--Sterile abscesses
• Cholera/typhoid--Tenderness, induration

Adverse effects should be reported to VAERS at the Dept. of Health and Human Services: (800) 822-7267.

Source: 1994 Red Book: Report of the Committee on Infectious Diseases. 23rd ed. Elk Grove Village, IL: American Academy of Pediatrics, 1994.

What Medical Students Can Do
As health care providers, medical students see a large number of patients who are eligible for immunizations. On pediatric and family practice clerkships, students have the opportunity to routinely administer vaccines and address preventive issues with patients and their families. Students also encounter adults who are eligible for influenza, pneumococcal and diphtheria-tetanus vaccines during their internal medicine rotations. One of the most effective ways of improving immunization levels is by getting involved in provider education.

Here are some suggestions:

• Educate yourself. Read widely. Seek out lectures on preventive care and attend public health courses. Consider getting an MPH. Several medical schools have opportunities for earning a joint MD-MPH degree, and a few residencies now offer an MPH with residency training.
• Educate your peers. Prepare a presentation during your pediatrics, internal medicine or family practice rotation about missed opportunities, screening for overdue immunizations, interventions to improve immunization rates within your clinic, identifying and reporting vaccine-preventable diseases, and educating parents on immunizations and other preventive issues.
• Educate your teachers. Assist your primary care site in auditing the immunization status of children and adults in its practice.
• Sponsor a brown bag lunch on immunization issues such as the provider's role in administration of vaccines, public health agencies and delivery of immunization services, or important local immunization issues and strategies to improve and sustain immunization levels. Pediatricians and other generalists interested in preventive care, as well as local and state health officials, would make excellent speakers.
• Sponsor a panel discussion on funding for immunizations. Who should pay for vaccines? Parents? Insurance companies? What responsibility do pharmaceutical companies have? How much should and can the government contribute? What is the provider's role? Invite representatives from all of these groups.
• Design and distribute pocket cards on invalid contraindications and adverse reactions to vaccines for medical students and residents to carry around in their white coats. See Figures 3 and 4 for suggestions on what to include.
• Develop a health survey on critical preventive care issues such as lead screening, injury prevention and immunizations for use on pediatric rotations. In one study, the provider's use of prompting sheets to discuss preventive services with the patient was one of the strongest predictors of complete immunization in children.15
• Develop a survey for adults including cholesterol, weight loss, pap smears, stool guiac tests and immunizations.

Provider-education materials are available from the National Immunization Program at the CDC, which publishes the Immunization Action News: (404) 639-8226. Information on assessment services is also available at this number. To learn more about surveillance and vaccine-preventable diseases, the CDC offers a live satellite downlink interactive course. For information, call (404) 639-8225. The National Center for Education in Maternal and Child Health is another excellent source for informational materials: (703) 524-7802. Call the AMSA Resource Center for the Immunization National Project Manual at (703) 620-6600, ext. 217.

Figure 4. Absolute Contraindications for Childhood Immunizations

• General--Anaphylactic reaction to any vaccine precludes further administration of the same vaccine.
• DTP/DTaP --Encephalopathy < 7 days following prior dose
• OPV--HIV infection or immunodeficiency in patient or household contact
• IPV--History of anaphylactic reaction to neomycin or streptomycin
• MMR--History of anaphylactic reaction to neomycin or streptomycin; pregnancy
• Hib--None
• HBV--None

Source: Plotkin and Mortimer. Vaccines, 2nd ed. Philadelphia: Saunders, 1993.994.

Community Outreach
Community outreach activities are crucial to boosting and sustaining immunization rates. Your key contact is the immunization specialist at your local health department. In many communities, coalitions of local health officials, business people, community organizations and individuals have a coordinated plan for identifying and vaccinating underserved children. The immunization specialist will help you maximize your efforts by focusing you on active community issues. Another important contact is the local school district, particularly for sixth graders due for measles vaccines. If grassroots activities are not in place in your community, here are some strategies for outreach:

• Assess underimmunization. Join/create a task force to examine deficits in delivery of immunizations in your community; disseminate this information to providers, health officials, members of the community and legislators. Write a plan to immunize all children.
• Promote the medical home. Volunteer at a public clinic to identify children who are behind on immunizations and use mail, telephone or canvassing to bring children back to the clinic. Work with interested obstetrics and pediatrics preceptors in speaking to pre- and postnatal mothers about well-baby care, including immunizations. Give community presentations on preventive care, including immunizations. Be aware that one-day immunization fairs and clinics can hurt the establishment of continuous care in a medical home.
• Promote vaccination in less politically visible populations, such as college students and adults over age 50, through informational fliers on campuses, in grocery stores and at shopping malls. The phone number of your local health department is located in the blue pages under "Local Government." Other organizations that can help you make local contacts and offer suggestions for community-outreach projects include: the Children's Action Network, (202) 338-7227; Every Child By Two (202) 651-7226; Immunization Education and Action Committee with Healthy Mothers, Healthy Babies, (202)863-2458; and the Immunization Action Coalition, (612) 647-9009. For information on activism and adult immunizations, contact the National Coalition for Adult Immunization at (301) 656-0003.

Figure 5. National Vaccine Advisory Committee Standards: formulated in response to the Measles Epidemic, 1989-1991.

1. Immunization services are readily available.
2. There are no barriers or unnecessary prerequisites to the receipt of vaccines.
3. Immunization services are available free or for a minimal fee.
4. Providers utilize all clinical encounters to screen for needed vaccines and, when indicated, to vaccinate children.
5. Providers educate parents and guardians about immunizations in general terms.
6. Providers question parents or guardians about contraindications and, before vaccinating a child, inform them in specific terms about the risks and benefits of the vaccinations their child is to receive.
7. Providers follow only true contraindications.
8. Providers administer simultaneously all vaccine doses for which a child is eligible at the time of each visit.
9. Providers use accurate and complete recording procedures.
10. Providers co-schedule immunization appointments in conjunction with appointments for other child health services.
11. Providers report adverse events following vaccination promptly, accurately and completely.
12. Providers operate a tracking system.
13. Providers adhere to appropriate procedures for vaccine management.
14. Providers conduct semi-annual audits to assess immunization coverage levels and to review immunization records in the
15. patient populations they serve.
16. Providers maintain up-to-date, easily retrievable medical protocols at all locations where vaccines are administered.
17. Providers practice patient-oriented and community-based approaches.
18. Vaccines are administered by properly trained persons.
19. Providers receive ongoing education and training regarding current immunization recommendations.

Influencing Legislation
Underlying legislative debate on childhood immunizations is who should pay for vaccines and associated services. The government currently pays out a number of entitlements; pharmaceutical companies sell vaccines to the government at steep discounts. Should and can each of these players contribute more? Law requires insurers to cover childhood immunizations, and many HMOs cover immunizations in the interest of preventive medicine. However, ERISA plans, which small businesses utilize, are exempt from covering immunizations. Should we require every health insurer (who will profit from reduced morbidity among clients) to fund immunizations?

Lobbying is an effective way for medical students to work for health care reform. Public health and preventive care should be integrated into these reforms. Medical students concerned with improving preventive services can support programs that support surveillance and provider assessment as well as education on vaccines and vaccine-preventable diseases. Programs that purchase vaccines are also helpful in establishing a medical home for children.

The local health department is an excellent source to help identify local legislative priorities. Again, you can find the health department's telephone number in the blue pages of the telephone book under "Local Government."

Medical students can make an impact on legislation by organizing letter-writing campaigns directed at members of state and national legislatures. Effective ways of lobbying your legislator include writing a personal letter or making a scheduled visit explaining who you are, what programs you feel the legislator should support, and why. Follow up these efforts with a phone call to the appropriate staff member. See the GPIT Project-in-a-Box titled Legislative Skills for Future Generalists for more information. More information about writing effective letters and lobbying members of the legislature is available here on AMSA's web page under legislative affairs. Or you can contact AMSA's Legislative Affairs Director at (703) 620-6600, ext. 211, for a package of information on effective lobbying. Your national legislator's office is available through the Capitol switchboard at (202) 224-3121.

Figure 6. Where to get started on the Web

Community Outreach:

Every Child By Two - check out the "Take Action!" at http://www.ecbt.org

Immunization Action Coalition: http://www.immunize.org

National Coalition for Adult Immunization: http://www.medscape.com/ncai

 

Provider Education:

National Immunization Program at the CDC. Download a copy of the Immunization Action News, the CDC's immunization newsletter for providers: http://www.cdc.gov/nip

The Future for Immunizations
Vaccines allow us to work toward eradicating disease for good. The elimination of small pox in 1977 demonstrates that this is a viable, and worthy, goal. During the 1990s, a number of promising changes have resulted in more children than ever having vaccines available at low cost with improved continuity of care. Heightened awareness and administration of adult immunizations is beginning to happen. Combination vaccines are now available that make immunization easier for parents and patients by reducing the number of injections children must receive. Through continued research and development, someday there may be a single, oral vaccine for all preventable diseases.

Following the burst of outbreaks in the late 1980s and subsequent interventions at the public health, community and private provider levels, childhood immunization rates have begun rising and the incidence of preventable disease is now waning. By 1996, all of the vaccine-preventable diseases, with the exception of whooping cough, were experiencing a decrease in the number of cases per annum. A great danger is that these promising pieces of news may result in laxity of action and a shift of attention away from populations such as the elderly, who are at substantial risk for morbidity and mortality from influenza and pneumococcal infections.

By being informed and active as a medical student, you can play a large role in sustaining the level of quality of health care provision by making preventive services more readily available. However, responsibility for medical education and training will rest largely in your hands. You will choose whether or not to pursue further education on immunization and other preventive issues. You will choose whether or not to promote education about these issues among peers. Legislative activity will carry on whether or not you participate in the dialogue.

Hopefully, medical schools will be leaders and not followers in teaching and delivering preventive health care. This will require immediate initiative and sustained change: HMOs, with a prevention-driven agenda and globally lower costs, are beginning to supplant the type of health care delivered in academic settings.22 Without provider input, business people and hospital administrators concerned with costs may become the driving force for change in medical education.

The quality of the public health in America depends on provider participation. Medical students, as health care practitioners, have a chance to form lasting partnerships with public health organizations concerned with immunization services and to deliver excellent care to individual patients that is informed by knowledge of the public health interest. In addition, medical students can champion the cause of preventive care for the underserved. Without vigilance, the poor, particularly young children and the elderly, will become or remain invisible to the health care system. As Phyllis Freeman, an attorney who is active in immunization politics, wrote: "A policy decision to leave some individuals outside the health care system does not remove their contribution to health or disease in the United States."23 This is of great concern to any physician who believes in preventive medicine and who cares for patients who belong to a community.

As informed medical students, we now have the opportunity to contribute to the dialogue on reform in health care delivery and medical education and to help alleviate disease and suffering that is so clearly and simply preventable.

References

1. The National Vaccine Advisory Committee. The measles epidemic: the problems, barriers, and recommendations. JAMA 1991; 266:1547-1552.
2. Centers for Disease Control and Prevention. Status Report on the Childhood Immunization Initiative: reported cases of selected vaccine-preventable diseases - United States, 1996. MMWR 1997; 46:665-671.
3. Plotkin and Mortimer. Vaccines, 2nd ed. Philadelphia: Saunders; 1994.
4. Centers for Disease Control and Prevention, unpublished data, 1993
5. Teitelbaum MA, Franklin, PC. Vaccine-preventable illness in US children 1980-1992. Statistical Bulletin 1994; Oct-Dec:2-9.
6. Bates AS, Fitzgerald JF, Dittus RS, Wolinsky FD. Risk factors for underimmunization in poor urban infants. JAMA 1994; 272:1105-1110.
7. Bobo JK, Gale JL, Thapa PB, Wassilak, SGF. Risk factors for delayed immunization in a random sample of 1,163 children from Oregon and Washington. Pediatrics 1993; 91:308-314.
8. Wright JA, Marcuse EK. Immunization Practices of Washington State Pediatricians-1989. AJDC 1992; 146:1033-1036.
9. Hueston WJ, Mainous AG, Palmer C. Delays in childhood immunization in public and private settings. Archives of Pediatric and Adolescent Medicine 1994; 148:470-473.
10. Marks JS, Halpin TJ, Irvin JJ, Johnson DA, Keller JR. Risk factors associated with failure to receive vaccines. Pediatrics 1979; 64:304-309.
11. Hueston WJ, Mainous AG, Farrell JB. Childhood immunization availability in primary care practices: effects of programs providing free vaccines to physicians. Archives of Family Medicine 1994; 3:605-609.
12. Grabowsky M, Orenstein WA, Marcuse EK. The critical role of provider practices in undervaccination. Pediatrics 1996; 97: 735-737.
13. Holt E, Guyer B Hughart N, Keane V, Viver P, Ross A, Strobino D. The contribution of missed opportunities to childhood underimmunization in Baltimore. Pediatrics 1996; 97:474-80.
14. Rodewald LE. Reliability of vaccination cards and parent-derived information for determining immunization status: lessons from the 1994 National Health Interview Survey (NHIS) provider record check (RC) study. American Pediatric Society/Society for Pediatric Research 1997 Abstract.
15. Bordley WC, Margolis PA, Lannon CM. Delivery of immunizations and other preventive services in private practice. Pediatrics 1996; 97: 467-
16. King GE, Hadler SC. Simultaneous administration of childhood vaccines: an important public health policy that is safe and efficacious. Pediatric Infectious Disease Journal 1994; 13:394-407.
17. Centers for Disease Control and Prevention. Reported vaccine-preventable diseases - United States, 1993, and the Childhood Immunization Initiative. MMWR 1994; 43:57-60.
18. LeBaron CW, Chaney M, Baughman AL, Dini EF, Maes E, Dietz V, Bernier R. Impact of measurement and feedback on vaccination coverage in public clinics, 1988-1994. JAMA 1997; 277:631-635.
19. Pierce C, Goldstein M, Suozzi K, Gallaher M, Dietz V, Stevenson J. The impact of the standards for pediatric immunization practices on vaccination coverage levels. JAMA 1996; 276:626-30.
20. Birkhead GS, LeBarn CW, Parsons P, Grabau JC, Barr-Gale L, Fuhrman J, Brooks S, Rosenthal J, Hadler SC, Morse, DL. The immunization of children enrolled in the special supplemental food program for women, infants, and children (WIC). JAMA 1995; 274: 312-316.
21. Chiu TT. Community mobilization for preschool immunizations: the "Shots by Two" project. Am J Public Health 1997; 87: 462-3.
22. For an excellent discussion of managed care and HMOs, see the GPIT Project-in-a-Box on Academic Medicine and Managed Care: An Uncertain Future. AMSA, Reston, VA, 1997.
23. Freeman P. National health care reform minus public health: a formula for failure. The John W. McCormack Institute of Public Affairs, University of Massachusetts, Boston, 1994.
24. Schlenker TL, Bain C, Baughman AL, Hadler, SC. Measles herd immunity: the association of attack rates with immunization rates in preschool children. JAMA 1992; 267: 823-826.
25. Centers for Disease Control and Prevention. Missed opportunities for pneumococcal and influenza vaccination of Medicare pneumonia inpatients - 12 western states, 1995. MMWR 1997; 46: 919-923.
26. Fedson DS. Adult immunization. Summary of the National Vaccine Advisory Committee Report. JAMA 1994; 272:1133-1137.
27. Centers for Disease Control and Prevention. Pneumococcal and influenza vaccination levels among adults aged > 65 years - United States, 1995. MMWR 1997; 46: 913-919.

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