Ineffectiveness of historical data in predicting measles susceptibility.

The Immunization Practices Advisory Committee ( ACIP ) has devised noninvasive, historical criteria for determining individuals who are susceptible to measles. These criteria, which involve proof of vaccination, are incorporated into school entrance regulations and are used to indicate people who require vaccination during outbreaks. In a recent measles epidemic in El Paso , TX, 120,000 records were screened using these criteria, and as a result 13,000 students were vaccinated. During this outbreak, 91 adolescents, who were susceptible to measles by ACIP criteria, were serologically tested for measles antibody. Although none of these students had documentation of vaccination, only 11.0% of them lacked measles hemagglutination-inhibiting (HAI) antibody at a titer of 5. Assuming a minimum cost for vaccine of +2.60 per dose, a conservative estimate of the cost to the El Paso Health Department for 20,000 doses of measles vaccine would be +52,000. If these data can be extrapolated to the total student population, then upwards of 85% of vaccinated students were already immune. Thus, +44,200 was spent unnecessarily. In addition, as the ACIP criteria did not select for measles susceptibility, an estimated 12,000 students in El Paso were not protected against measles. Other methods to determine measles susceptibility should be developed for optimal control of future outbreaks.