Harmony on the second dose of measles vaccine.

Abstract

Since 1989 the disparate recommendations of the Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics' (AAP) Committee on Infectious Diseases (COID), “The Redbook Committee,” regarding the age at which the second dose of measles vaccine (usually measles, mumps, rubella [MMR]) should be given has posed a dilemma for pediatricians. Although the goals of each group were identical, the pragmatic aspects considered by the respective committees differed. The ACIP, focusing primarily on the public health community, knew that immunizing the “captive audience” at school entry would be the most efficient way of assuring administration of a second dose. The COID, focusing primarily on the practicing clinician, judged that the second dose at 10 to 12 years would more rapidly provide protection for those youngsters who had been primary failures in the second year of life and were now approaching secondary school and university where many of the “breakthrough” cases of measles were occurring in the mid-1980s. Additionally, the AAP was encouraging the adoption of a “routine” adolescent visit during which the MMR could be administered.The resurgence of measles during 1989–1991 with >55 000 cases and 150 deaths alerted the nation to the major problem residing in populations of inner-city, indigent minority children who never received a first dose of vaccine. The issue of second doses faded to a lower priority. With the mobilization of national efforts to overcome the poor immunization status of these populations, primary measles vaccination by age 2 years reached all-time heights in 1995 and 1996 with 80% to 90% achievement. For the first time since measles reporting was initiated, there have been <1000 cases each year since 1993. Of equal importance has been the absence since 1993 of any “US strain” of measles virus circulating in the country. Molecular epidemiology has demonstrated the foreign origin of all strains submitted for analysis to the Centers for Disease Control and Prevention. A third element contributing further to a lowered rate of importation to the United States has been the Pan American Health Organization's success in eliminating measles from much of the remainder of the western hemisphere.1In their study of 26 550 youngsters in the Oakland and Seattle areas, Davis et al2 have reviewed the reactions and adverse events noted after a second dose of MMR administered at 4 to 6 years compared with a dose administered at 10 to 12 years. Their data indicate a more likely clinical event in the 30 days after vaccination of 10- to 12-year-olds rather than 4- to 6-year-olds but none was of major significance.What is the pediatrician to do? The ACIP and COID have now agreed that the second MMR may be administered anytime after the first (given at 12 to 15 months of age) as long as a minimum of 1 month separates the two. Because of requirements for school entry, the majority of children will undoubtedly receive their second dose at the earlier age. In those states where such requirements do not exist, pediatricians may use their own judgment as to when a second dose is given. It is important to remember that the primary failure rate after initial MMR is approximately 5%. A second dose given after the proper interval will result in successful immunization of 95% of these initial 5% failures. Previous concern regarding waning immunity (secondary failures) that might be prevented by delaying the second dose is obviated by studies showing the rate of waning immunity after measles vaccine is <0.2%.34 The data accumulated by Davis et al2 add further justification for the earlier age of second dose administration. The goal of measles elimination early in the 21st century should be attainable and may render this question moot.