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Vaccination of Internationally Adopted Children

The ability of a clinician to determine that a person is protected on the basis of their country of origin and their records alone is limited. Internationally adopted children should receive vaccines according to recommended schedules for children in the United States. Only written documentation should be accepted as evidence of prior vaccination. Written records are more likely to predict protection if the vaccines, dates of administration, intervals between doses, and the child's age at the time of immunization are comparable to the current U.S. recommendations. Although vaccines with inadequate potency have been produced in other countries (139,140), the majority of vaccines used worldwide are produced with adequate quality control standards and are potent.

The number of American families adopting children from outside the United States has increased substantially in recent years (141). Adopted children's birth countries often have immunization schedules that differ from the recommended childhood immunization schedule in the United States. Differences in the U.S. immunization schedule and those used in other countries include the vaccines administered, the recommended ages of administration, and the number and timing of doses.

Data are inconclusive regarding the extent to which an internationally adopted child's immunization record reflects the child's protection. A child's record might indicate administration of MMR vaccine when only single-antigen measles vaccine was administered. A study of children adopted from the People's Republic of China, Russia, and Eastern Europe determined that only 39% (range: 17%--88% by country) of children with documentation of >3 doses of DTP before adoption had protective levels of diphtheria and tetanus antitoxin (142). However, antibody testing was performed by using a hemagglutination assay, which tends to underestimate protection and cannot directly be compared with antibody concentration (143). Another study measured antibody to diphtheria and tetanus toxins among 51 children who had records of having received >2 doses of DTP. The majority of the children were from Russia, Eastern Europe, and Asian countries, and 78% had received all their vaccine doses in an orphanage. Overall, 94% had evidence of protection against diphtheria (EIA > 0.1 IU/mL). A total of 84% had protection against tetanus (enzyme-linked immunosorbent assay [ELISA] > 0.5 IU/mL). Among children without protective tetanus antitoxin concentration, all except one had records of >3 doses of vaccine, and the majority of nonprotective concentrations were categorized as indeterminate (ELISA = 0.05--0.49 IU/mL) (144). Reasons for the discrepant findings in these two studies probably relate to different laboratory methodologies; the study using a hemagglutination assay might have underestimated the number of children who were protected. Additional studies using standardized methodologies are needed. Data are likely to remain limited for countries other than the People's Republic of China, Russia, and Eastern Europe because of the limited number of adoptees from other countries.

Physicians and other health-care providers can follow one of multiple approaches if a question exists regarding whether vaccines administered to an international adoptee were immunogenic. Repeating the vaccinations is an acceptable option. Doing so is usually safe and avoids the need to obtain and interpret serologic tests. If avoiding unnecessary injections is desired, judicious use of serologic testing might be helpful in determining which immunizations are needed. This report provides guidance on possible approaches to evaluation and revaccination for each vaccine recommended universally for children in the United States (see Table 6 and the following sections).

MMR Vaccine

The simplest approach to resolving concerns regarding MMR immunization among internationally adopted children is to revaccinate with one or two doses of MMR vaccine, depending on the child's age. Serious adverse events after MMR vaccinations are rare (6). No evidence indicates that administering MMR vaccine increases the risk for adverse reactions among persons who are already immune to measles, mumps, or rubella as a result of previous vaccination or natural disease. Doses of measles-containing vaccine administered before the first birthday should not be counted as part of the series (6). Alternatively, serologic testing for immunoglobulin G (IgG) antibody to vaccine viruses indicated on the vaccination record can be considered. Serologic testing is widely available for measles and rubella IgG antibody. A child whose record indicates receipt of monovalent measles or measles-rubella vaccine at age >1 year and who has protective antibody against measles and rubella should receive a single dose of MMR as age-appropriate to ensure protection against mumps (and rubella if measles vaccine alone had been used). If a child whose record indicates receipt of MMR at age >12 months has a protective concentration of antibody to measles, no additional vaccination is needed unless required for school entry.

Hib Vaccine

Serologic correlates of protection for children vaccinated >2 months previously might be difficult to interpret. Because the number of vaccinations needed for protection decreases with age and adverse events are rare (24), age-appropriate vaccination should be provided. Hib vaccination is not recommended routinely for children aged >5 years.

Hepatitis B Vaccine

Serologic testing for HBsAg is recommended for international adoptees, and children determined to be HBsAg-positive should be monitored for the development of liver disease. Household members of HBsAg-positive children should be vaccinated. A child whose records indicate receipt of >3 doses of vaccine can be considered protected, and additional doses are not needed if >1 doses were administered at age >6 months. Children who received their last hepatitis B vaccine dose at age <6 months should receive an additional dose at age >6 months. Those who have received <3 doses should complete the series at the recommended intervals and ages (Table 1).

Poliovirus Vaccine

The simplest approach is to revaccinate internationally adopted children with IPV according to the U.S. schedule. Adverse events after IPV are rare (4). Children appropriately vaccinated with three doses of OPV in economically developing countries might have suboptimal seroconversion, including to type 3 poliovirus (125). Serologic testing for neutralizing antibody to poliovirus types 1, 2, and 3 can be obtained commercially and at certain state health department laboratories. Children with protective titers against all three types do not need revaccination and should complete the schedule as age-appropriate. Alternately, because the booster response after a single dose of IPV is excellent among children who previously received OPV (3), a single dose of IPV can be administered initially with serologic testing performed 1 month later.

DTaP Vaccine

Vaccination providers can revaccinate a child with DTaP vaccine without regard to recorded doses; however, one concern regarding this approach is that data indicate increased rates of local adverse reactions after the fourth and fifth doses of DTP or DTaP (42). If a revaccination approach is adopted and a severe local reaction occurs, serologic testing for specific IgG antibody to tetanus and diphtheria toxins can be measured before administering additional doses. Protective concentration** indicates that further doses are unnecessary and subsequent vaccination should occur as age-appropriate. No established serologic correlates exist for protection against pertussis.

For a child whose record indicates receipt of >3 doses of DTP or DTaP, serologic testing for specific IgG antibody to both diphtheria and tetanus toxin before additional doses is a reasonable approach. If a protective concentration is present, recorded doses can be considered valid, and the vaccination series should be completed as age-appropriate. Indeterminate antibody concentration might indicate immunologic memory but antibody waning; serology can be repeated after a booster dose if the vaccination provider wishes to avoid revaccination with a complete series.

Alternately, for a child whose records indicate receipt of >3 doses, a single booster dose can be administered, followed by serologic testing after 1 month for specific IgG antibody to both diphtheria and tetanus toxins. If a protective concentration is obtained, the recorded doses can be considered valid and the vaccination series completed as age-appropriate. Children with indeterminate concentration after a booster dose should be revaccinated with a complete series.

Varicella Vaccine

Varicella vaccine is not administered in the majority of countries. A child who lacks a reliable medical history regarding prior varicella disease should be vaccinated as age-appropriate (8).

Pneumococcal Vaccines

Pneumococcal conjugate and pneumococcal polysaccharide vaccines are not administered in the majority of countries and should be administered as age-appropriate or as indicated by the presence of underlying medical conditions (26,43).

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