Serologic testing to verify the immune status of internationally adopted children against vaccine preventable diseases

Abstract

Definitive immunization guidelines for internationally adopted children are lacking. We examined whether these children had serologic evidence of protection against vaccine-preventable diseases. For children with ≥3 vaccine doses, overall protection was high for diphtheria (85%), tetanus (95%), polio (93%), hepatitis B (77%), and Hib (67%). For children ≥12 months of age with ≥1 dose of measles, mumps, or rubella vaccines, 95%, 72%, and 94% were immune, respectively. Children without immunization documentation had lower immunity. Serologic testing was useful in verifying the immunization status in internationally adopted children with and without documentation of immunizations.

Introduction

In 2008, 17,443 children were internationally adopted by families in the United States (US) and more than 200,000 children were adopted in the past decade [1]. The American Academy of Pediatrics (AAP) recommends that children undergo a comprehensive health assessment shortly after arrival to the US, including an assessment of previously administered vaccines [2]. While the Advisory Committee on Immunization Practices (ACIP) [3], the Infectious Disease Society of America (IDSA) [4], and the AAP [2] provide several options for assuring that internationally adopted children are properly immunized, no clear consensus exists about which strategy is optimal. Written records may be accepted as valid if: the vaccines, dates of administration, numbers of doses, intervals between doses, and patient's age at the time of immunization are all consistent with the current US or World Health Organization schedule. Serologic testing may also be used to verify the child's immunizations. Another option provided is to give one dose of vaccine and do serologic testing one month later. If there are concerns about whether vaccines were administered properly or were immunogenic, repeat administration of immunizations is recommended.

The lack of definitive recommendations for immunization decisions in internationally adopted children is likely due to the varied results from previously published studies [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. The interpretation and comparison of results from these studies may differ due to differences in laboratory methods and definitions of protection. In addition, many of these studies have small sample sizes, minimal country-specific data, and evaluated only a few vaccine antigens. Serologic testing has been used in research settings in vaccine development and post-licensure surveillance to verify response to vaccine antigens and to provide a surrogate for protection [16]. In addition, many health care providers, employers, and public health agencies utilize serology in populations such as military recruits, health care workers, and pregnant women to document their immune status and to determine their potential need for immunization [3], [4]. Since serum antibody testing is widely accepted as a method to verify immunity [3], [4], [16], we have routinely used serologic testing to guide our recommendations for immunization in internationally adopted children. To assist in providing data for evidence-based guidelines, the objective of our study was to determine whether internationally adopted children had serologic evidence of protection against vaccine preventable diseases and to determine if documentation of immunization was associated with protective antibody levels.