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Polio eradication

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    Perhaps it's too early for a full throated crow but we're nearly there, you know: polio should soon go the way of smallpox. In 1999 there were just over 7000 cases of poliomyelitis in the world and during the first half of 2000 there were under 700 cases and 154 isolates of wild poliovirus. The virus is now transmitted in only 30 countries, in South Asia and West and Central Africa (T Jacob John. New England Journal of Medicine 2000;343:806–7 [editorial]).  In many developing countries antibody responses to oral poliovaccine (OPV), especially to type 1 and 3 virus, are less than in richer countries. Since 1990, infants in Oman have routinely been given five doses of OPV, at birth, at 40 days and at 3, 5, and 7 months. Of 1025 nine month old infants studied in 1992–93 (Roland W Sutter and colleagues. New England Journal of Medicine 2000;343:767–73) 97% were seropositive for type 1 poliovirus, 98% for type 2, and 88% for type 3. They were randomly assigned to one of four supplemental, single dose vaccine options: inactivated poliovirus vaccine (IPV), American-made trivalent OPV, European-made trivalent OPV, or monovalent type 3 OPV. After 30 days none of the OPV options had had any significant effect on type 3 virus antibody titres or seroprevalence but in the infants given IPV, type 3 virus seroprevalence had increased to 97% and median type 3 antibody titre from 1 in 228 to 1 in 1448. The rapid increase in titre was taken to indicate a secondary immune response.  It is suggested that once wild poliovirus has been eliminated from a country or region, IPV should be used until global eradication is confirmed. A single dose of IPV costs more than a dose of OPV but IPV vaccination is cheaper because fewer doses are needed. In his editorial, T Jacob John points to the occurrence of vaccine related poliomyelitis and states that polio eradication should mean the elimination of any poliovirus, wild or vaccine strain, from people everywhere. He does not comment directly about the implications for vaccination programmes in the richer countries although he refers, with approval, to experience with IPV in Scandinavia.

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