The effect of epidemic measles on immunization rates.

OBJECTIVE

To evaluate whether immunization against a vaccine-preventable disease is sought to avoid the naturally occurring disease itself, we hypothesized that the rate of "on-time" measles immunization would increase during an epidemic of that disease. If such an effect occurred, we wondered whether it would have an impact on on-time administration of other recommended immunizations.

DESIGN

Retrospective evaluation of immunization rates of children at their second birthday with the use of computerized health records of children entering kindergarten in an 8-year interval spanning the onset of epidemic measles in Chicago, Ill, in 1989 and 1990.

SETTING

Children entering Chicago public schools.

MAIN OUTCOME MEASURES

Rates of receipt of measles-containing vaccine (MCV), 1 to 4 doses of a diptheria toxoid-tetanus toxoid-pertussis (DTP) or diphtheria toxoid-tetanus toxoid (DT) vaccine, 1 to 3 doses of oral or inactivated polio vaccine (OPV/IPV), and the full series 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 increased from 56% to 58% in the years prior to 70% during the epidemic (1989 and 1990). A similar increase did not occur to DTP/DT 4 or OPV/IPV 3. Moreover, among older children delayed in MCV receipt, evidence of catch-up immunization also occurred during the epidemic years; similar catch-up for delayed DTP/DT 4 or OPV/IPV 3 immunization did not occur.

CONCLUSIONS

Dramatic increases in one-time and catch-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 suggests MCV receipt was not associated with receipt of other recommended immunizations during that time.