LESSONS FROM CUBA - MASS CAMPAIGN ADMINISTRATION OF TRIVALENT ORAL POLIOVIRUS VACCINE AND SEROPREVALENCE OF POLIOVIRUS NEUTRALIZING ANTIBODIES

The immunogenicity of trivalent oral poliovirus vaccine (TOPV), which is less effective in tropical than in temperate areas, may potentially be improved in several ways, including increasing the number of doses . Little information is available on TOPV when more than 6 doses are g iven. The situation in Cuba provides a unique opportunity to relate th e seroprevalence of neutralizing antibodies to the dose of TOPV becaus e Cuba has not reported culture-confirmed poliomyelitis since 1973 and TOPV is only administered in twice yearly 1-week mass immunization ca mpaigns. Sera from 2000 children nationwide were studied for neutraliz ing antibody among children who received 0, 2, 4, 6 and 8 doses of TOP V. These doses were administered in the period 1989-91, when TOPV (fro m the USSR) was being used with 500 000, 200 000, and 300 000 median t issue-culture-infecting doses (TCID50) for types 1, 2 and 3, respectiv ely-the 5:2:3 formulation. Seroprevalence of neutralizing antibody aft er two TOPV doses was 91.5% for type 1, 90.8% for type 2, and 45.9% fo r type 3. Seroprevalence of type-3 neutralizing antibody after 6 doses remained low (73.4%), but increased to 83.5% after 8 doses (P < 0.05) . Although 16.5% of the children remained unprotected for type-3 infec tion even after 8 doses, mass campaign immunization strategies were su fficient to eradicate the transmission of wild poliovirus in Cuba. Bec ause the seroprevalence of type-1 neutralizing antibody was high (91.5 %) after two campaign doses, additional studies using different formul ations are needed to determine whether simultaneous improvement in the type-3 response to two campaign doses can be achieved.