Immunity to poliovirus among children and the elderly in north-east Italy

Italy and Europe were declared polio-free in June 2002, but increasing migration, even from undeveloped countries where polio still exists, may lead to a come-back of circulating poliovirus (PV) and infection in previously polio-free areas. It is consequently advisable to continue to monitor the immunity of the population in polio-free areas. The aim of this study was to assess the current prevalence of neutralizing antibodies in recently-immunized children and in elderly people who were never vaccinated.

Sera from 511 healthy subjects resident in the Veneto Region were examined to assay their antibody titer for PV 1, 2 and 3, using the microneutralization test. Data were analyzed by chi-squared test, Student's t-test and linear regression analysis, using EPI-Info 2000 supplied by the Centers for Disease Control and Prevention (Atlanta, GA, USA).

Neutralizing antibodies in group A (231 subjects aged 1-17 years) showed significantly higher geometric mean titers (GMTs) than in group B (280 subjects aged 65-100 years) for all three PV serotypes (P < 0.001). Nobody simultaneously lacked neutralizing antibodies for all three serotypes. There were no difference between the two groups in terms of male/female GMTs for the three PV Antibodies decreased with time since vaccination, but the difference was only significant for PV 3. GMTs were lower in the elderly, with no significant difference among the three PV.

The population examined showed a good level of protection against the three PV strains: both groups A (vaccinated) and B (naturally immunized) revealed a valid immunity to poliovirus.

Immunization programs and immunity status population screening are still advisable until polio has been world-wide eradicated.