Vaccine Extraimmunization—Too Much of a Good Thing?

The article by Feikema and colleagues¹ in this issue of THE JOURNAL suggests that extraimmunization of children occurs considerably more often than previously appreciated. Using data from the National Immunization Survey, Feikema et al examined the immunization histories of more than 22,000 children aged between 19 and 35 months. The National Immunization Survey used 2 steps to collect information: in the first, parents with eligible children were identified, and in the second, the child's immunization records were obtained from their health care provider. The proportion of children who received extra immunization doses ranged, by individual vaccine, from 2.5% for measles-containing vaccine to more than 14% for poliovirus vaccine. Taken together, up to 21% of all children were reported to have received at least 1 extra immunization before their third birthday. In the multivariate analysis of risk factors for extraimmunization, Feikema and colleagues found that children with more than 1 health care provider were almost 3 times more likely to be extraimmunized compared with children with a single provider. Extraimmunization not only wastes vaccine, money, and labor, but unnecessary doses add to a child's stress and discomfort, increase the risk for adverse events following vaccination, and may lead to confusion among parents and health care providers about what vaccines have, and have not, actually been administered. The authors conclude that more attention needs to be focused on the problem of duplicate immunization.

Although these findings are striking, it is important to consider whether the rates of extraimmunization have been overestimated before they prompt changes in physician practice. Documentation errors occur in immunization records, as in other medical records, and can be substantial.² When records from different health care providers (or multiple records from the same provider) are combined for the purposes of research, some errors, such as date transpositions, would cause a single immunization to appear more than once and thus be counted as an extra immunization. Other errors, such as misinterpretation of vaccine trade names while transcribing historical records, also could lead to errors in documentation. While these errors would have been counted in the current study as extraimmunization, in fact, extra vaccinations may not have been administered.

It is important to realize that not all extraimmunization is necessarily inappropriate. In recent years, the immunization schedule has become considerably more expanded; up to 16 injections currently are recommended during the first 2 years of life.³ At some visits, up to 4 separate injections may be indicated, and this number will increase if the new pneumococcal conjugate vaccine is added to the schedule later this year, as anticipated. To reduce the number of injections a child receives during clinic visits, pharmaceutical companies have developed combination vaccines, but these present challenges to clinicians faced with patients in need of only 1 of the antigens at a single visit. In a report to help guide physicians on the use of combination vaccines, the Advisory Committee on Immunization Practices, the American Academy of Pediatrics, and the American Academy of Family Physicians recognized the problems and expense of stocking all available vaccine types or products.⁴ The report concluded that it is acceptable for physicians to administer extra antigens when a combination vaccine would reduce the required number of injections, or if it is the only means of delivering the indicated antigen.

Feikema et al also suggest that immunization registries would improve the quality of immunization data and help physicians vaccinate each child appropriately and on time. These registries would gather data from those who deliver vaccinations and supply this information to physicians, clinics, health departments, health maintenance organizations, and others involved with immunizations. A centralized registry also might help eliminate duplicate documentation and reduce time spent acquiring immunization history. Furthermore, registries could prepare call-back reports for children who are behind on immunizations, identify high-risk groups for targeted outreach, prepare coverage reports for medical practices or plans, and expedite the documentation of vaccination status for patients entering schools, daycare, or new jobs.^{5 - 6}

However, immunization registries face a number of challenges, primarily those of technology, data, confidentiality, beliefs, and money.⁷ Registries have to accommodate a diverse assortment of equipment, data transferring capabilities, and computer savvy. Getting participants successfully connected has turned out to be far more complex, time-consuming, and expensive than originally anticipated.⁸ Data accuracy and confidentiality are another hurdle; even with complete names and birth dates it is challenging to rapidly link vaccines to individuals using automated means, making rapid access to historical vaccine data difficult. The attitudes and beliefs of some physicians present another barrier, because physicians notoriously overestimate the immunization coverage levels in their own patient panels.⁹ Hence, some physicians may not agree with the need for a new registry, especially one that incurs additional cost. Moreover, the issue of long-term financing of population-based registries is still largely unresolved in most communities, and it is not clear whether federal or state governments will be willing to allocate the considerable amount of money necessary for sustained funding of such registries.

The study by Feikema and colleagues has several important larger implications. The National Immunization Survey was performed in 1997, around the time that the American Academy of Pediatrics initially recommended the expanded use of inactivated poliovirus vaccine for routine childhood immunization.¹⁰ The findings by Feikema et al raise the intriguing question of whether changing the recommended schedule confused physicians and led to extraimmunization with polio vaccine. It would have been instructive if the investigators had looked at the frequency of extraimmunization over time. Doing so could have helped determine whether the pronounced excess in poliovirus immunization was clustered in the period immediately following the release of the new recommendations or has been an ongoing, yet unrecognized, problem. A clear finding of extraimmunization associated with vaccine schedule changes would have important policy implications and would suggest the need for monitoring this type of impact with future immunization schedule changes. Such a finding also would highlight the need for special educational campaigns for physicians and nurses about new vaccines or vaccine schedule changes.

Although the data reported by Feikema et al are important, they are not sufficient to prompt changes in current immunization practice. In the United States, immunization coverage today is higher, and mortality due to vaccine-preventable diseases is lower, than ever before.¹¹ However, trust in the vaccine delivery system can be easily disturbed, as demonstrated in the United Kingdom when unproven allegations linking measles-mumps-rubella (MMR) vaccine to autism led to lower MMR vaccine coverage.^{12 - 13} When coverage falls, the consequences can be severe, as seen in the recent massive diphtheria epidemics in the former Soviet Union republics,¹⁴ and in the pertussis epidemics of the 1970s and 1980s in various countries.¹⁵

While continued research into the extent and causes of extraimmunization is needed to help formulate proper intervention strategies, additional work can be done now. Proper immunization practice is grounded in the availability of accurate and timely information about the vaccination history. There is a clear need for a nationally standardized, easily used immunization form to reduce confusion and error. Additionally, the study by Feikema et al highlights the difficulty of tracking all the vaccines a child receives over his or her lifetime. For lasting solutions it will be important to continue to develop registries that help link children's immunization histories across multiple providers. Technologic solutions (such as the use of barcodes) will likely be necessary to create rapid and highly accurate means to enter data on administered vaccines into medical records or immunization registries.⁵

For parents and physicians who need to decide what to do with this new information now, it is important to recognize that the risk of withholding vaccinations still far outweighs concerns about cost or the small added risk of adverse events associated with extraimmunization. Clinicians should continue to use each health care visit as an opportunity to immunize every child. However, the study by Feikema et al provides a timely reminder that more attention needs to be paid to extraimmunization, and that a concerted effort is needed to secure a complete and accurate immunization history for each child.