Seroprevalence of antibody against poliovirus in inner-city preschool children. Implications for vaccination policy in the United States.

OBJECTIVES

To assess susceptibility to poliomyelitis in selected inner-city preschool children in the United States and to estimate the contribution of secondary spread of live attenuated oral poliovirus vaccine virus to type-specific immunity.

DESIGN

Cross-sectional seroprevalence study.

METHODS

Serum neutralizing antibody levels against poliovirus types 1, 2, and 3 were analyzed according to vaccination status, age, and other sociodemographic variables.

SETTING

Hospital and satellite clinics serving inner-city populations in Houston, Tex, and Detroit, Mich, 1990 to 1991.

PARTICIPANTS

A total of 526 children aged 12 to 47 months seeking medical care were enrolled in the seroprevalence study; 144 children aged 12 to 35 months without a history of previous oral poliovirus vaccination were enrolled in the secondary spread study.

RESULTS

Seropositive rates were similar in children in both cities, ranging from about 80% for types 1 and 3 in 12- to 23-month-old children to more than 90% in those aged 36 to 47 months. The most important predictor of seropositivity was the number of doses of oral poliovirus vaccine received (P < .01), with levels approximately 90% for all 3 serotypes among children who had received 3 or more doses. In children likely to have been unvaccinated, seropositive rates ranged from 9% to 18% for poliovirus types 1 and 3 and from 29% to 42% for type 2; secondary spread of vaccine virus appeared to have occurred among children who had previously received 1 dose or less but not those with 2 or more doses.

CONCLUSIONS

Levels of immunity to poliovirus among inner-city preschoolers are high and may be predicted by the number of doses of oral poliovirus vaccine received. Secondary spread of the vaccine virus plays a modest role in increasing polio immunity in inner-city populations, especially against types 1 and 3. This role will decrease in importance if the recently attained high levels of immunization coverage in the United States are sustained and if the risk of importation of wild poliovirus continues to diminish.