Immunogenicity of a supplemental dose of oral versus inactivated poliovirus vaccine.

In many developing countries, the immunogenicity of three doses of live, attenuated, oral poliovirus vaccine (OPV) is lower than that in industrialised countries. We evaluated serum neutralising antibody responses in 368 children aged 6 months and 346 children aged 9 months in Côte d'Ivoire who had previously received three doses of OPV at 2, 3, and 4 months of age, and who were then randomised to receive a supplemental dose of OPV or enhanced-potency inactivated poliovirus vaccine (IPV) at the time of measles vaccination. Although both vaccines increased seroconversion to all three poliovirus types, antibody responses were greater in the IPV group. Among children with no detectable antibody at baseline, IPV was 2 to 14 times more likely than OPV to induce seroconversion (type 1, 80% vs 40% at 6 months [p < 0.001] and 81% vs 14% at 9 months [p < 0.001]; type 3, 76% vs 22% at 6 months [p < 0.001], and 67% vs 5% at 9 months [p < 0.001]. Among children with detectable antibody at baseline, IPV was 1.4 to 7 times more likely than OPV to elicit 4-fold or more rises in antibody titre (p < 0.01). Geometric mean titres (GMTs) to all three poliovirus types were also consistently higher among IPV recipients than in OPV recipients when measured 4-6 weeks and 13-17 months after vaccination. Administration of a supplemental dose of IPV or OPV, which requires no additional visits or changes in the existing immunisation schedule, might improve protection against paralytic poliomyelitis in communities with suboptimum seroconversion rates after three doses of OPV.

Evaluation of an intervention program in the control of an urban outbreak of shigellosis.

Community-wide outbreaks of shigellosis are a persistent public health problem. We evaluated the effect of a household-based intervention program on the control of an urban outbreak of S. sonnei gastroenteritis. During the intervention we attempted to contact all households with culture-confirmed S. sonnei and provide education in methods to prevent spread of Shigella. Subsequently we conducted a survey of intervention (n = 43) and nonintervention (n = 33) households. We also conducted a serosurvey of children three to five years of age. The number of new cases of S. sonnei infection declined steadily over several months after the intervention began. Members of the intervention households were more knowledgeable about handwashing (rate ratio [RR] 4.7, 95% confidence interval [CI] = 2.1-10.8) and others methods of S. sonnei transmission and control than members of nonintervention households. However, intervention households had higher attack rates of Shigella-associated diarrhea in susceptible household members (RR 1.4, 95% CI = 1.0-2.0). During the intervention we were able to contact only 25% of households by the eighth day after onset of diarrhea in the index case, when 90% of intrahousehold transmission of Shigella had already occurred. Two months after the outbreak ended, 42% of children in the outbreak community had elevated antibody titers against S. sonnei; an additional 19% had borderline elevated titers. The intervention program improved knowledge but may have occurred too late to prevent intrahousehold transmission of Shigella. Exhaustion of susceptible hosts, rather than the education program, likely accounted for the decline in shigellosis cases.(ABSTRACT TRUNCATED AT 250 WORDS)