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that intramuscular injections administered during the per cent of children aged one to seven years old were incubation period of wild-type poliovirus infection reported to have received a dose of trivalent oral polio increased the risk of paralytic disease (a phenomenon vaccine. The authors concluded that the mass known as ‘provocation’ poliomyelitis). We conducted a vaccination campaign may only have been partially case-control study to explore the association between successful in ending the epidemic. intramuscular injections and vaccine-associated Wyatt (1987) addressed another well-known problem poliomyelitis in Romania. of provocation poliomyelitis caused by injections of DPT “Of the 31 children with vaccine-associated disease, together with OPV in The Gambia. This phenomenon 27 (87 percent) had received one or more intramuscular was addressed in the above section on Romania. injections within 30 days before the onset of paralysis, compared with 77 of the 151 controls (51 percent) _ Paralytic poliomyelitis outbreak in Namibia (matched odds ratio, 31.2; 95 percent confidence Van Niekerk et al. (1994) described an outbreak of interval, 4.0 to 244.2). Nearly all the intramuscular paralytic poliomyelitis in Namibia. They wrote: "The injections were antibiotics, and the association was last confirmed cases of poliomyelitis in Namibia had strongest for the patients who been reported in 1988. However, received 10 or more injections between November 8, 1993, and (matched odds ratio for more or equal anuary 7, 1994, 27 cases of paralytic 10 injections as compared with no poliomyelitis were confirmed in the injections, 182.1; 95 percent The same situation country. The outbreak was limited to confidence interval)." . as he south health region; at least 80% So, the risk of paralysis was strongly of poliomyelitis of infants in this region have received associated with injections given after occurring in fully our doses of oral poliovaccine (OPV) the oral polio vaccine, but not with by the age of | year. The patients injections given before or at the same time vaccinated ranged from 13 months to 12 years; 24 as the vaccine. However, in a cases, children, usually were younger than 5 years. ol the 26 was given simultaneously wi : patients whose vaccine status was DPT vaccine. straight after mass nown, 14 had received four doses of Interestingly, as reported by Strebel vaccination drives OPV, 6 had one or two doses, and 6 no b] vaccine." The normal health services and hence vaccination in the north had been severely disrupted by a long war. Interestingly, the authors reasoned that since due to poor vaccination efforts the wild poliovirus was circulating freely in the northern health region, children developed — solid immunity to it (without developing paralysis). This interesting and important information was repeated by Poliomyelitis epidemic in The Gambia Biellik et al. (1994), who wrote: "In late 1993 a Otten et al. (1992) and Deming et al. (1992) reported on poliomyelitis epidemic occurred almost exclusively in he epidemic in The Gambia of poliomyelitis associated residents of the south health region [the area that was with type | poliovirus involving 305 cases (estimated ighly vaccinated]. We speculate, therefore, that 986 population of 768,995) from May to November endemic wild poliovirus circulation continued 986, following a six-year non-epidemic period with only uninterrupted in Angola and the two north regions of ive reported cases. The highest attack rate was in one- amibia across the well-travelled border since 1989, year-old children: 394 cases per 100,000 of population. | when cases were last reported. Although OPV coverage The national attack rate was 40 per 100,000 of _ was fairly low in northern compared with southern et al. (1995), the timing of the onset of paralysis, with IM injections given after DPT and OPV, was 9-30 with a median of 16 days (the highest risk being at 8-14 days, 15-21 days and 22-30 days), and 0-7 days and 15-21 days with DPT and OPV injections given before the onset of paralysis. This reflected the phenomenon of critical days as discovered and defined by Scheibner (2004). has occurred in many other countries, both developed and developing. population. A vaccination coverage survey showed that amibia, a higher proportion of northern children may 64 per cent of one- to two-year-old children were ave been protected, at least to type I, by natural vaccinated with at least three doses of trivalent oral immunity, thus suppressing epidemics. In 1993 OPV3 polio vaccine at the beginning of the epidemic. Fifty; | coverage among infants aged less than | year was seven cases became paralysed more than two weeks igher in the south than the north. However, evidence after a national mass vaccination campaign, in which 95 suggests that a substantial pool of susceptibles, per cent of children aged one to seven years old were reported to have received a dose of trivalent oral polio vaccine. The authors concluded that the mass vaccination campaign may only have been partially successful in ending the epidemic. Wyatt (1987) addressed another well-known problem of provocation poliomyelitis caused by injections of DPT together with OPV in The Gambia. This phenomenon was addressed in the above section on Romania. of poliomyelitis occurring in fully vaccinated children, usually straight after mass vaccination drives, many other countries, both developed and developing. Poliomyelitis epidemic in The Gambia Otten et al. (1992) and Deming et al. (1992) reported on the epidemic in The Gambia of poliomyelitis associated with type | poliovirus involving 305 cases (estimated 1986 population of 768,995) from May to November 1986, following a six-year non-epidemic period with only five reported cases. The highest attack rate was in one- year-old children: 394 cases per 100,000 of population. The national attack rate was 40 per 100,000 of population. A vaccination coverage survey showed that 64 per cent of one- to two-year-old children were vaccinated with at least three doses of trivalent oral polio vaccine at the beginning of the epidemic. Fifty- seven cases became paralysed more than two weeks after a national mass vaccination campaign, in which 95 NEXUS ¢ 29 The same situation has occurred in OCTOBER - NOVEMBER 2009 www.nexusmagazine.com