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Physician Knowledge of Catch-up Regimens and Contraindications for Childhood Immunizations

Nicole J. Cohen, MD^*, Diane S. Lauderdale, PhD, Priya B. Shete, BA^*, John B. Seal, MA^* and Robert S. Daum, MD^*

^* Pediatric Immunization Program, the Department of Pediatrics
Department of Health Studies, University of Chicago, Chicago, Illinois

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	ABSTRACT

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
Objectives. To determine physician success at designing catch-up regimens for children delayed in immunizations and physician knowledge regarding contraindications to immunization.

Methods. A self-administered survey was completed by pediatricians, general practitioners, and family practitioners in Cook County, Illinois. Surveys included 6 open-ended vignettes describing hypothetical children delayed in immunization for whom participants were asked to design catch-up regimens. Bivariate and multivariate logistic regression were used to determine predictors of correct response. The surveys also inquired about management of scenarios that might be perceived as contraindications to immunize with the Haemophilus influenzae type b or measles-mumps-rubella vaccines.

Results. The mean score of correct responses was 1.83 of a possible 6.0. Almost one third of respondents answered all 6 vignettes incorrectly. The proportion of incorrect responses was high for all 6 vignettes (39%–86%), but higher for questions that addressed the immunization of children older than 12 months. Errors in vaccine administration were most commonly attributed to omitted vaccines, with varicella-zoster vaccine and pneumococcal conjugate vaccine omitted most frequently. Pediatricians were >4 times more likely to answer correctly than were family practitioners. Participants in the Vaccines for Children (VFC) program were more than twice as likely to answer correctly than were non-VFC providers. Knowledge of contraindications was inconsistent, particularly for measles-mumps-rubella vaccine.

Conclusions. Childhood vaccine providers have substantial knowledge deficits of recommended immunization schedules and vaccine contraindications that may contribute to missed opportunities to immunize. Pediatricians and participants in the VFC program were more successful at designing catch-up regimens for children with immunization delay.

Key Words: vaccination • immunization • immunization delay • children • provider practices • vaccine contraindications

Abbreviations: AAP, American Academy of Pediatrics • ACIP, Advisory Committee on Immunization Practices • VFC, Vaccines for Children • AMA, American Medical Association • Hib, Haemophilus influenzae type b • MMR, measles-mumps-rubella • HIV, human immunodeficiency virus • VZV, varicella-zoster vaccine • DTaP, diphtheria-tetanus-acellular pertussis • PCV, pneumococcal conjugate vaccine • IPV, inactivated polio vaccine

	INTRODUCTION

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A secondary effect of our highly successful immunization program is the increasing complexity of the schedule for receipt of recommended immunizations. A child immunized according to the current recommendations of the American Academy of Pediatrics (AAP) and the Advisory Committee on Immunization Practices (ACIP)^1,2 will receive up to 23 injectable doses of single or combination vaccines before school entry. The complexity of the vaccine schedule creates a difficult task for the clinician faced with an underimmunized child. Crucial factors in correcting vaccination delay are the availability of the child’s immunization record, as well as the physician’s knowledge of the immunization schedule, recognition of immunization delay, and willingness to administer vaccines when the opportunity presents itself. In addition, physicians must have information regarding appropriate strategies for vaccine catch-up.

Missed opportunities for immunization occur most commonly at acute illness visits, often associated with provider misconceptions of contraindications for immunization.^3–6 In this instance, no vaccines are given.

Visits during which some but not all vaccines required for catch-up are administered have been demonstrated to contribute to immunization delay in an inner-city reminder-recall program.⁷ The occurrence of such incomplete vaccine administration suggests that physicians may have difficulty constructing catch-up regimens, particularly when children are delinquent in multiple vaccines. Alternatively, physicians may face parental resistance toward a large number of simultaneous injections. This issue becomes especially important in a child with known vaccine noncompliance, as the physician has no assurance that the child will return if a catch-up plan is formulated that requires >1 visit.

Since the early 1990s, local health departments and the federal government have implemented programs to remove economic barriers to childhood immunization. The Vaccines for Children (VFC) program was established in 1994 to provide vaccines free of charge to physicians and clinics caring for children of Native American or Alaskan descent, Medicaid recipients, children who are uninsured, or those whose health insurance does not cover immunizations.⁸ Evaluations of the VFC program to date suggest that VFC providers are less likely to refer children to public vaccine clinics.^8–11 Since the program’s inception, rates of immunization coverage have improved, mirroring the decrease in public health referrals.⁸

Because visits where some but not all required vaccines were given occurred frequently in an underimmunized population that we had studied,⁷ we hypothesized that some physicians may experience difficulty in determining appropriate strategies for correcting immunization delay for a given child. Therefore, the primary objectives of this study were 1) to determine the success of physicians at designing catch-up regimens for children delayed in immunizations and 2) to determine the knowledge of physicians regarding contraindications to immunization. We also examined provider approaches to correcting immunization delay and the types of errors made by physicians when designing catch-up regimens.

	METHODS

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Subjects and Survey Administration
We obtained a list of all pediatricians and family/general practitioners, including MDs and DOs practicing in Cook County, Illinois, from the American Medical Association (AMA) in June 2001. From 2270 names, a random two thirds sample was drawn (n = 1513) to receive a self-administered survey that was mailed to participants with a cover letter explaining its purpose. A second mailing was sent 5 months later to nonrespondents. Surveys were coded numerically to allow respondent anonymity. The survey protocol was approved by the Institutional Review Board of the University of Chicago, which indicated that neither written or oral informed consent was required for this study.

Questions
The survey instrument was modeled on that used by Wood et al¹² in 1992. They solicited the design of catch-up regimens for 3 hypothetical children (ages 5, 9, and 12 months) delinquent in immunizations, and presented 6 scenarios addressing possible contraindications to receipt of specific vaccines. Our survey used the 3 vignettes of Wood et al and an additional 3 that addressed catch-up immunization regimens for older children (15 months, 2 and 5 years), as well as 5 possible contraindication scenarios (Table 1) created by one of us (R.S.D.).

A second set of questions addressed immunization contraindications with regard to Haemophilus influenzae type b (Hib) and measles-mumps-rubella (MMR) vaccines, representative of bacterial component and live viral vaccines, respectively. Five scenarios described commonly encountered situations that might incorrectly be considered contraindications to administration of either or both vaccines. Three scenarios described situations relating to the immune status of the child (inhaled steroids) or a family member (human immunodeficiency virus [HIV] infection or chemotherapy). Two scenarios described temporary situations (fever or receipt of antibiotics for an acute infection) where a physician might elect to defer immunization due to personal judgment or parental preference.

Scoring of Responses
We used recommendations of the AAP and ACIP to evaluate responses,^1,2 scoring each vignette according to the completeness and timing of vaccine administration. Since the vignettes provided for 2 patient encounters, we anticipated use of 2 different approaches to design a catch-up regimen. A more aggressive approach would administer all delinquent vaccines (up to 7 injections in some scenarios) at the initial visit, with subsequent doses administered at an appropriately spaced second visit. A less aggressive approach would use 2 visits to administer all relevant vaccines and specify a temporally proximate interval between them. Both approaches were scored correct if all required vaccines were included in the 2 visits. We allowed up to 8 weeks to complete vaccine administration using the less aggressive strategy.

Responses were scored as incorrect if physicians made any of the following errors: omission of any age-appropriate vaccine in the 2 encounters; administration of unnecessary doses, for example, 2 doses of Hib after 15 months of age; administration of age-inappropriate vaccines, for example, varicella-zoster vaccine (VZV) or MMR before 1 year of age; administration of sequential doses separated by an inappropriate time interval, for example, 2 doses of diphtheria-tetanus-acellular pertussis (DTaP) vaccine <4 weeks apart; or nonsimultaneous administration of 2 live virus vaccines (MMR or VZV) <4 weeks apart. Since the recommended immunization schedule is flexible in the age of administration for certain vaccines (for example, VZV may be given at 12–18 months), we did not count as incorrect any omission before the upper limit of the age range.

Statistical Analysis
The study population was described with respect to demographic characteristics provided by the AMA database and practice-related variables included in the survey.

We categorized correct responses to each vignette as using the more aggressive or less aggressive strategies. For incorrect responses, we classified errors as those of omission, unnecessary or age-inappropriate administration, or inappropriate interval timing, and analyzed them for each vaccine individually and all vaccines combined. Using vignette 5 (Table 1), we determined the number of vaccines physicians were willing to administer at 1 visit. Vignette 5 required the highest number of vaccines (7). We performed a subanalysis of this vignette excluding pneumococcal conjugate vaccine (PCV) and VZV, the 2 vaccines added most recently to the recommended immunization schedule. The purpose was to determine if error rates were much lower if these 2 vaccines were excluded.

For each respondent, the number of correct vignettes was summed to create a single score ranging from 0 to 6. Participants were then divided according to whether they scored above (2) or below (1) the mean correct score. This variable was analyzed as the outcome in a logistic regression model to determine if demographic or practice-related variables predicted a higher score. First, bivariate analyses tested the association between scoring above or below the mean and each demographic or practice-related variable. Variables evaluated included gender, location, year of medical school graduation, medical school location, academic affiliation, specialty, percentage of patients younger than 5 years, proportion of uninsured patients and those receiving Medicaid, level of participation in the VFC program, and the number of patient encounters in a typical day that resulted in administration of vaccines. The dichotomized score was also tested in a multivariate logistic regression model, including the above variables. Each variable’s significance in the model was tested using either the likelihood ratio or Wald test. We were concerned that some variables were highly correlated with each other and would be colinear if entered simultaneously in a regression model. Specifically, the degree of participation in the VFC program was highly correlated with the proportion of patients receiving Medicaid (Spearman’s rank correlation coefficient = 0.75), and the number of vaccine encounters in a typical day was correlated with the proportion of patients younger than 5 years (Spearman’s = 0.66). Since participation in VFC and the number of vaccine encounters in a typical day were of greater interest, the other 2 variables were omitted from the multivariate model. We did not find a high correlation between participation in VFC and either the proportion of uninsured patients (Spearman’s = 0.36) or the number of vaccine encounters in a typical day (Spearman’s = 0.16).

For the 5 possible contraindication scenarios, we determined the proportion of physicians who would choose not to give either MMR or Hib vaccines under the described circumstances.

Nonresponse Analysis
To determine if respondents differed from nonrespondents with respect to vaccine knowledge, we performed 3 analyses. First, respondents and nonrespondents were compared using demographic variables provided by the AMA. Second, respondents to the first and second mailings were compared according to the mean number of correct responses to the catch-up vignettes. Comparisons were performed using either ² or Student t test. Also, a randomly chosen subsample of nonrespondents was contacted by telephone and asked to complete a shortened version of the demographic portion of the survey and a single vignette, to ascertain whether immunization knowledge of nonrespondents differed substantially from respondents. Vignette 5 was selected for this purpose as it was the question containing the fewest details of vaccine history, and provided sufficient variability in preliminary analysis.

Data were analyzed using STATA 7 (STATA Corporation, College Station, TX).

	RESULTS

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Study Participants
We received completed surveys from 550 physicians, 457 after the first mailing and 93 after the second mailing. One hundred and twenty-two surveys were returned uncompleted. Most of these were undeliverable by the postal service, or included a self-imposed reason for ineligibility (eg, retired, subspecialist, does not see children). Therefore, the response represents 40% of the adjusted survey sample (1391 recipients).

Demographic characteristics of respondents and nonrespondents are compared in Table 2. A higher proportion of female recipients, pediatricians, and US medical school graduates completed the survey. Respondents graduated from medical school more recently than nonrespondents. Practice characteristics of respondents are presented in Table 3. More than half the respondents were pediatricians. Fifty percent reported administering vaccines in >5 patient encounters in a typical day, and 61% reported some participation in the VFC program.

View larger version (37K): [in this window] [in a new window]   Fig 1. Vignette 5 subanalysis—number of doses administered at a single visit.

View larger version (29K): [in this window] [in a new window]   Fig 2. Vignette 5 subanalysis with exclusion of PCV and/or VZV.

Factors associated with an above average score using bivariate analysis included female gender, specialization in pediatrics, academic affiliation, urban location, higher proportion of patients younger than 5 years, more vaccine encounters in a typical day, participation in the VFC program, and higher proportion of patients receiving Medicaid (Table 6). When the predictors were entered into a multivariate logistic regression model (Table 7), VFC providers were more than twice as likely to achieve an above average score. Pediatricians were 4.3 times more likely than family practitioners and 2.9 times more likely than practitioners in other fields to score above average. Female physicians were 50% more likely to score above average than were male physicians. Although a higher number of vaccine encounters in a typical day was strongly predictive of correct response in the bivariate analysis, this variable was confounded in the multivariate model by specialty and participation in the VFC program.

View larger version (50K): [in this window] [in a new window]   Fig 3. Proportion of respondents considering scenarios a contraindication for MMR or Hib. indicates MMR; , Hib.

	DISCUSSION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
We found that physicians are not proficient at designing catch-up regimens for children with immunization delay. Furthermore, correct responses were less frequent for scenarios involving older children. Previous studies have shown that problems maintaining on time immunization compliance typically worsen after the first year of life.^13–15 Our data provide a possible clue as to one reason why this occurs, ie, physicians may be less familiar with immunization recommendations for older children. Catch-up regimens for older children are likely more difficult to design because of greater divergence from the standard schedule of administration and the complex recommendations for Hib and PCV for older children. In response to our opinion question, 81% of respondents agreed that the catch-up regimens were difficult or very difficult to design.

Except for the case of the 5-month-old child, physicians tended to use the less aggressive strategies when designing catch-up regimens. We previously found that the rate of on-time compliance with all age-appropriate immunization recommendations could have been 20% to 44% higher had all doses required for catch-up been administered at visits where at least 1 of the missing immunizations were administered.⁷ Thus, provider difficulty in constructing catch-up immunization regimens and/or decisions to implement less aggressive catch-up strategies may have a relatively unappreciated impact on immunization rates. The less aggressive catch-up strategies still fell within the recommended ACIP/AAP guidelines. However, choosing to defer immunizations in a child with known immunization delay results in a missed opportunity to immunize if the child fails to return for the follow-up necessary to complete a "less aggressive" strategy.

Among respondents, pediatricians were more likely to design correct catch-up regimens than were family practitioners. Such differences in correct responses may be attributed to differences in training or experience with pediatric patients and well child care. A study based on data by the National Immunization Survey found that children immunized solely by pediatricians were 1.63 times more likely to be up to date than those immunized by family practitioners.¹⁶

Physicians providing immunizations through the VFC program were significantly more successful at designing catch-up regimens than those not participating in the program. The association of participation in the VFC program and knowledge of immunization catch-up is difficult to explain. It is possible that VFC providers are more likely to encounter children with immunization delay, and thus have greater familiarity with catch-up regimen design. However, data from the National Immunization Survey did not demonstrate increased immunization coverage among patients immunized by VFC providers.¹⁶

Individual errors in creating catch-up regimens were predominantly due to the omission of vaccines. VZV and PCV, the 2 newest vaccines recommended for routine pediatric administration, were omitted most frequently. Routine administration of VZV has been controversial, with a number of physicians choosing not to recommend the vaccine for their patients, and a high proportion of parents refusing it.¹⁷ It is likely that the extreme newness of PCV and physician unfamiliarity with the vaccine contributed to the high omission rate of this vaccine.

The highest proportion of unnecessary vaccine doses was for Hib, likely reflecting errors in understanding the complexity of age-associated recommendations for this vaccine. Age-associated errors were also evident for DTaP and PCV, including both unnecessary doses for older children and inappropriate timing of sequential doses, again suggesting that physicians are more familiar with vaccine recommendations for infants than for children older than 12 months.

The results of the contraindication scenarios suggest that physicians have substantive knowledge gaps regarding immunization contraindications. The high proportion of physicians who would defer MMR vaccine attributed to immunodeficiency in a family member is particularly concerning. Failure to immunize with MMR in such circumstances is incorrect for 2 reasons: 1) the live attenuated viruses contained in the vaccine are not transmissible to contacts¹; and 2) the immunocompromised family member is at increased risk of infection if exposed to wild-type virus transmitted from an unimmunized contact.

The major limitation of our study is the relatively low survey response rate of 40%. Mailed physician surveys are typically responded to at a rate of 50%.¹⁸ We did not prescreen survey recipients for eligibility; many may have been ineligible because of factors such as retirement, migration, or type of practice. This possibility is supported by the fact that 8% of our survey questionnaires were returned unanswered for these sorts of reasons. Our survey was long and challenging, resulting in a high responder burden. Although limited by sample size, the results of our nonresponse analysis suggest that nonresponders are no more likely than responders to correctly design catch-up regimens. In fact, the higher proportions of responders who were female, pediatricians or US medical graduates were likely, given our findings, to bias our sample toward higher knowledge. Another limitation is the artificiality of the survey situation that may not accurately reflect the resources (for example nursing staff) that a physician may draw on in the design of actual catch-up regimens. We would have liked to compare our results with those of Wood et al¹² to determine if the increased complexity of the immunization schedule has made catch-up regimens more difficult to design. However, we were unable to do so because of the aggregate presentation of their data.

The high error rate in response to our catch-up vignettes, combined with the predominant opinion of survey respondents regarding the difficulty of the task, suggests a need for educational opportunities as well as practice aids to assist physicians in the design of catch-up vaccine regimens. Improving physician knowledge of the recommended immunization schedule as well as contraindications to immunization should reduce the number of missed opportunities to immunize and improve overall immunization coverage among children at high risk for immunization delay.

	ACKNOWLEDGMENTS

 
The Pediatric Immunization Program receives financial support from Aventis, the Chicago Department of Public Health, GlaxoSmithKline, and the University of Chicago Hospitals. Additional nonfinancial support is received from Americorps VISTA.

Note Added in Proof. During the revision of this manuscript, a 5-valent combination vaccine was licensed (PEDIARIX, GlaxoSmithKline). Use of this product might affect provider decisions to construct "more aggressive" or "less aggressive" catch-up scenarios in their responses and might alter some data in the "Required Doses" calculations in Table 4.

	FOOTNOTES

 
Received for publication Jul 19, 2002; Accepted Nov 12, 2002.

Address correspondence to Robert S. Daum, MD, Section of Pediatric Infectious Diseases, University of Chicago Hospitals, 5841 S Maryland Ave, MC 6054, Chicago, IL 60637. E-mail: rdaum{at}peds.bsd.uchicago.edu

	REFERENCES

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 

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This Article Abstract Full Text (PDF) P3Rs: Submit a response Alert me when this article is cited Alert me when P3Rs are posted Alert me if a correction is posted Citation Map Services E-mail this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My File Cabinet Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via ISI Web of Science (12) Citing Articles via Google Scholar Google Scholar Articles by Cohen, N. J. Articles by Daum, R. S. Search for Related Content PubMed PubMed Citation Articles by Cohen, N. J. Articles by Daum, R. S. Related Collections Infectious Disease & Immunity Related AAP Red Book topics: Haemophilus influenzae Infections

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