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Am J Public Health. 2002 February; 92(2): 266–270.
PMCID: PMC1447054

Childhood Vaccination Providers in the United States

Abstract

Objectives. This study sought to provide a characterization of US childhood vaccination providers.

Methods. The state was used as the analytic unit in examining 1997 data from the National Immunization Survey and the Vaccines for Children program, state immunization reports, and natality records.

Results. Overall, 57% of children were vaccinated in the private sector, 18% were vaccinated in the public sector, and 25% were vaccinated by a mixture of providers. Of the 50 883 immunization sites, 81% were private and 19% public. Average patient load was 77 infants per site. Private-sector patient loads were lower than public-sector loads.

Conclusions. US childhood vaccination provider capacity is adequate. Efforts to raise coverage rates should focus on increasing preventive care use among children, improving the vaccination performance of providers, and ensuring continuity of care.

Well-child care may be the most important opportunity for prevention in the clinical health care system, and vaccination is commonly regarded as a core function.1 However, US immunization providers have never been characterized: How many practices and clinics provide vaccinations to children? How many children are served in the public and private sectors? What is the overall capacity of the system to deliver vaccinations to the birth cohort? How evenly is this capacity distributed? Two programs that had their first full year of implementation in 1995, the National Immunization Survey and the Vaccines for Children (VFC) program, made it possible to estimate provider counts on a state-by-state basis and thus answer these questions for the first time.

METHODS

We sought to estimate 3 variables on a state-specific basis.

(1) Proportion of children vaccinated in the public and private sectors. Following guidelines of the VFC program, we defined the public sector as including health care facilities under government chain of command. Public providers were categorized as health departments, community/migrant health centers, and “other” (e.g., city hospitals, the Indian Health Service, military clinics). We defined the private sector as comprising other facilities not under government chain of command (e.g., private practices, private hospital clinics). Thus, a county clinic was considered public even if it received most of its funds from private insurance reimbursement, whereas a physician in solo practice was considered private even if most of his or her income was derived from Medicaid.

(2) Number of vaccination provider sites. Following VFC guidelines, we defined a vaccination provider site as a health care facility where routine vaccinations were administered to children and medical records were kept. An individual site might have multiple physicians or no physicians (e.g., a public clinic staffed by nurse practitioners). A satellite site was counted separately if it maintained its own vaccination records.

(3) Average infant patient load per site.

Data Sources

All of the data collected for this study were for the year 1997.

National Immunization Survey (NIS).

The NIS furnishes annual population-based estimates of provider-verified immunization rates for children aged 19 to 35 months; methods used in calculating these estimates have been described in detail elsewhere.2 Briefly, telephone interviews based on random-digit dialing are completed for 440 children in each state. All health care providers for each child are contacted to verify immunizations, categorize the type of site in which they practice, and determine whether their site is enrolled in VFC. Final data are adjusted to account for nonresponse; the nonresponse rate in 1997 was 31% (range 11%–44%).3

VFC reports.

The VFC program supplies health care providers with federally purchased vaccines to be administered to children who are uninsured, eligible for Medicaid, Native American, or Alaska Native. From each state's annual VFC report, we obtained site counts categorized by vaccine distribution system: (1) universal (distribution to all providers of all vaccines approved for routine childhood use by the US Public Health Service Advisory Committee on Immunization Practices), (2) VFC public and private (VFC program enrollment open to all public and private providers), or (3) VFC public (VFC program enrollment open only to public providers).

State immunization reports.

From each state's annual immunization report, we abstracted counts of public clinics and then confirmed these counts with the state immunization program.

State natality data.

These data were derived from the National Center for Vital Statistics.4

Public–Private Proportions

To assess the proportion of children vaccinated in each sector, we analyzed NIS data and allocated children into one of 3 categories: (1) public (vaccinated entirely at public sites), (2) private (vaccinated entirely at private sites), or (3) mixed (vaccinated in both sectors or by providers whose sector was unknown).

Numbers of Provider Sites

For public sites, we used exact counts from state reports. In the case of private sites, 3 methods were employed. For states categorized as universal (n = 15), we used exact counts from the vaccine distribution program. For states categorized as VFC public and private (n = 14), we estimated the total number of private provider sites by dividing the count of private VFC sites by the state-specific proportion of private providers who, according to the NIS, were enrolled in the VFC. We tested the accuracy of this method in universal states; the estimate varied from the true count by less than 0.1% (5786 vs 5780).

Finally, for VFC public states (n = 2), we lacked any counts of private sites (VFC or otherwise), so we imputed numbers by assuming that the average private-sector infant patient load in these 2 states was the same as the average for the other states (53.7 infants per site). We then divided the state-specific number of infants vaccinated in the private sector (according to the NIS) by this average patient load. Again, we tested the accuracy of this method in universal states; the imputation varied from the true count by 7% (5375 vs 5780).

Infant Patient Load per Site

To estimate the average infant patient load per site, we divided the birth cohort by the number of vaccination sites in each state. To examine public–private site patient loads, we divided the number of infants vaccinated in each sector by the number of sites in each sector.

Statistical Analysis

While this study was primarily descriptive, we evaluated several associations using the state as the unit in an ecological analysis; SAS (version 6.12) was used in conducting this analysis. We examined the relationship of vaccine distribution system to proportion of children vaccinated in the private sector, and to proportion of sites in the private sector, using Wilcoxon rank sum tests. Using these same tests, we assessed the difference between public and private infant patient loads. To evaluate the extent to which the proportion of children vaccinated in the public sector correlated with the proportion of total sites in the public sector, we used the Spearman test.

RESULTS

Proportions of Infants Vaccinated

The majority (57%) of children were vaccinated solely in the private sector, but the range was wide (18%–79%; Table 1 [triangle]). More children were vaccinated in the mixed sector than solely in the public sector (25% vs 18%), although state-to-state variability was high (mixed sector: 13%–41%; public sector: 4%–56%). The 10 states with the highest private-sector proportions were contiguously located in the Northeast, and the 2 states with the lowest proportions were contiguously located in the South, but geographic patterns were not otherwise marked. Vaccine distribution system was not significantly associated with sector proportions.

Table 1
—Infants Vaccinated in Public and Private Sectors, Based on 1997 National Immunization Survey Data

Childhood Vaccination Providers

Of the 50 883 sites, 19% were public (range: 4%–72%), a percentage almost identical to the 18% of the birth cohort vaccinated in the public sector (Table 2 [triangle]). Also, proportion of public sites correlated positively with proportion of children vaccinated in the public sector (r = .572, P < .001). A similar correlation for the private sector (r = .553, P = .001) became stronger when mixed-sector children were assigned to the private sector as their probable medical home (r = .572, P < .001). Vaccine distribution system was not associated with sector proportions. Excluding the 2 states that did not offer the VFC program to private providers, private-sector VFC enrollment rates were high and were slightly elevated in states with vs without universal vaccine distribution (means of 89% and 86%, respectively, P = .025).

Table 2
—Childhood Vaccination Providers: United States, 1997

Infant Patient Loads

Overall, there was a ratio of 77 infants to each childhood vaccination site (3 894 968 infants at 50 883 sites), with an 11-fold range among states (17–191). Excluding mixed-sector infants, the patient load was significantly lower (P < .001) for private practices (average: 54; range: 12–136) than for public clinics (average: 73; range: 5–267). When mixed-sector infants were allocated to the private sector as their probable medical home, private–public patient loads became equivalent (i.e., 77 vs 73). When, instead, these infants were assumed to have been vaccinated in the public sector because they could not obtain vaccinations in the private sector, the discrepancy became very large (private: 54; public: 176; P < .001). States with high private patient loads tended to have high public patient loads (r = .405, P = .003). Universal vaccine distribution was associated with lower patient loads (P = .015).

DISCUSSION

In summary, we found that approximately 50 000 sites provided childhood vaccinations in the United States in 1997, of which 20% were public and 80% private, producing an average infant patient load of 77 per site with wide variability among states and between sectors. Overall, 57% of children were vaccinated in the private sector in 1997, consistent with the results of a preliminary 1995 study.5 If we assume that children vaccinated in the mixed sector had a private primary care provider, 82% of children could be considered the private sector's responsibility. If instead we assume that children vaccinated in the mixed sector went to public clinics to receive vaccinations that the private sector was unwilling to provide, then 43% of the birth cohort would fall into the public safety net. Although apparently contradictory, these interpretations have convergent implications: public-sector savings may be achieved through policies that support private-sector continuity of care.

Is the capacity of the US childhood vaccination provider system adequate? Because 4 adequately spaced visits can bring an infant to series completion,6 our data suggest that if each site were to appropriately vaccinate about 1 infant per workday (77 infants per site × 4 visits/250 workdays per year = 1.2 infants per workday), the US birth cohort would be age-appropriately vaccinated. If each US infant were to receive the 7 well-child-care (health supervision) visits recommended by the American Academy of Pediatrics,7 2 infants each day would need to be seen per site.

We have previously shown8 that a well-child-care visit, including vaccination, physician, and nurse time, averages about 20 minutes in duration. This suggests that preventive care for all US infants could be achieved by an average investment of less than 45 minutes per day per site. Even with the most extreme patient load revealed in our data (267 infants per clinic), vaccination of 4 children per day and health supervision for 8 children per day would achieve immunization and health supervision goals for the population served. Thus, capacity does not appear to be the rate-limiting step in US preventive care.

Capacity analysis, however, does not address issues of barriers to receipt of care. Increasing families' use of preventive services (e.g., reducing costs and dropout rates) and improving provider preventive care (e.g., reducing missed opportunities) may require more resources than are involved in actually providing vaccinations.

Our study has many limitations. The NIS estimates of public–private and VFC enrollment proportions were based on provider self-reports in a context of variable response rates. Although exact counts were available for all public sites, all VFC sites, and all private sites in universal states, we estimated private site numbers in 34 states and imputed them in 2 states. We did not obtain data on level of vaccination activity; thus, small, inactive sites were categorized together with large, active sites.

Nevertheless, our study indicates that the capacity of US childhood vaccination providers is adequate to achieve immunization goals.9 Efforts to raise coverage levels should focus on increasing use of preventive services, improving provider vaccination performance, and ensuring continuity of care.

Notes

C. W. LeBaron planned the study, analyzed the data, and wrote the paper. B. Lyons assisted in study design and analysis and was primarily responsible for study execution. M. Massoudi and J. Stevenson assisted in study conception, design, execution, and analysis.

Peer Reviewed

References

1. US Preventive Services Task Force. Guide to Clinical Preventive Services. 2nd ed. Baltimore, Md: Williams & Wilkins; 1996.
2. Zell ER, Ezzati-Rice TM, Battaglia MP, Wright RA. National Immunization Survey: the methodology of a vaccination surveillance system. Public Health Rep. 2000;115:65–67. [PMC free article] [PubMed]
3. Centers for Disease Control and Prevention. National, state, and urban area vaccination coverage levels among children aged 19–35 months—United States, 1997. MMWR Morb Mortal Wkly Rep. 1998;47:547–554. [PubMed]
4. Ventura SJ, Anderson RN, Martin JA, Smith BL. Births and deaths: preliminary data for 1997. Natl Vital Stat Rep. 1998;47:13 (Table 4). [PubMed]
5. Maes EF, Rodewald L, Coronado VG, et al. Who is immunizing children in the US: public or private providers? In: Program and abstracts of the 1998 Pediatric Academic Societies' Annual Meeting, May 1998, New Orleans, La. Abstract 112.
6. Centers for Disease Control and Prevention. Recommended childhood immunization schedule—United States, 2001. MMWR Morb Mortal Wkly Rep. 2001;50:7–19. [PubMed]
7. Guidelines for Health Supervision. 3rd ed. Elk Grove Village, Ill: American Academy of Pediatrics; 1997.
8. LeBaron CW, Rodewald LE, Humiston SG. How much time is spent on well-child care and vaccinations? Arch Pediatr Adolesc Med. 1999;153:1154–1159. [PubMed]
9. Healthy People 2000: National Health Promotion and Disease Prevention Objectives—Full Report With Commentary. Washington, DC: US Dept of Health and Human Services; 1991. DHHS publication PHS 91-50212.

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