THE EFFECT OF EPIDEMIC MEASLES ON IMMUNIZATION RATES

Objective.-To evaluate whether immunization against a vaccine-preventa ble disease is sought to avoid the naturally occurring disease itself, we hypothesized that the rate of ''on-time'' measles immunization wou ld increase during an epidemic of that disease. If such an effect occu rred, we wondered whether it would have an impact on on-time administr ation of other recommended immunizations. Design.-Retrospective evalua tion of immunization rates of children at their second birthday with t he use of computerized health records for children entering kindergart en in an 8-year interval spanning the onset of epidemic measles in Chi cago, III, in 1989 and 1990. Setting.-Children entering Chicago public schools. Main Outcome Measures.-Rates of receipt of measles-containin g vaccine (MCV), 1 to 4 doses of a diphtheria toxoid-tetanus toxoid-pe rtussis (DTP) or diphtheria toxoid-tetanus toroid (DT) vaccine, 1 to 3 doses of oral or inactivated polio vaccine (OPV/IPV), and the full se ries of these vaccines (4:3:1) that are required to be ''up-to-date'' by the second birthday. Results.-The rate of on-time MCV receipt incre ased from 56% to 58% in the years prior to the epidemic to 70% during the epidemic (1989 and 1990). A similar increase did not occur for DTP /DT 4 or OPV/IPV 3. Moreover, among older children delayed in MCV rece ipt, evidence of catch-up immunization also occurred during the epidem ic years; similar catch-up for delayed DTP/DT 4 or OPV/IPV 3 immunizat ion did not occur. Conclusions.-Dramatic increases in on-time and catc h-up MCV receipt occurred during the Chicago measles epidemic of 1989 and 1990. The lack of similar increases in DTP/DT 4 and OPV/IPV 3 sugg ests MCV receipt was not associated with receipt of other recommended immunizations during that time.