PERSISTENCE OF IMMUNITY TO POLIOMYELITIS AMONG A SOUTHERN-POPULATION THAT RECEIVED 4 DOSES OF OPV 5 TO OVER-15 YEARS BEFORE

The immune status against polioviruses was investigated in a populatio n of 545 students aged 11-20 years residing in the Neapolitan area, wh o had completed the vaccination cycle with four doses of OPV 5 to over 15 years before. Assuming as unprotected those individuals without de tectable neutralizing antibodies at the dilution 1:2, nobody resulted without protection against all types of poliovirus; 0.7% lacked antibo dies only against type 1, 0.6% only against type 3 and none against ty pe 2. A very slight decreasing trend was observed for GMT values in fu nction of the distance from the last dose of OPV for polio 1 and 2, bu t not for polio 3. As expected, GMT values for polio 2 resulted higher than those for polio 1 and both were higher than those for polio 3, w hen calculated by age groups as well as by distance groups. The last f our Italian cases of autoctonous paralytic poliomyelitis, occurred in the period 1981/83, regarded unvaccinated children aged 6 months - 2 y ears, residing in the same geographical area to which the study popula tion belong. In the same area a delay of immunization practices was al so ascertained in the recent past. Results of this study confirm that a priority for public health services is to devote their human and eco nomic resources to reduce the vaccination delay more than administrate a further fifth dose of OPV at the age of twelve.