RESUMEN
Longini and Halloran and Halloran et al. recently developed a method for estimation of parameters related to the efficacy of a vaccine and to the transmission of an infectious disease from time-to-event (disease or infection) data. This work uses their method to evaluate the individual and population effectiveness of a vaccination programme (Haber et al.). Data from an outbreak of measles in Chad illustrates the new methods.
Asunto(s)
Inmunidad , Modelos Estadísticos , Vacunación , Estudios de Evaluación como Asunto , Humanos , Funciones de Verosimilitud , Sarampión/inmunología , Sarampión/prevención & controlRESUMEN
A nationwide sample survey was conducted in Chad to establish the prevalence of iodine deficiency disorders (IDD). The country was stratified into the Sahel zone and the Sudan zone, the latter including the city of N'Djamena. The analysis followed a stratification whereby the city of N'Djamena was also separately analysed. A total of 1171 people between 10 and 20 years of age were included in the survey. The overall weighted prevalence of goitre, evaluated by a clinical examination, was 63%. In the Sudan zone the prevalence was 70%, in the Sahel zone 64% and for the capital, N'Djamena, 25%. There were significant differences in the frequency of goitre between the three zones. Females-as established in surveys from other areas and countries-had goitre significantly more often. The prevalence of cretinism varied between 0 and 1.2%, and was highest in the Sahel zone. Amongst the sampled population of the Sudan zone, 33% had less than 20 micrograms/l of urinary iodine, indicating severe iodine deficiency. In the Sahel zone and in N'Djamena the figures reached 8 and 1%. There were high levels of thiocyanate anions in urine reaching medians between 21 and 27 mg/l in the geographical stratas. This probably decreases the bio-availability of iodine. These data show that there is a high endemicity of goitre in Chad and provide a basis for interventions as part of a national action plan against IDD, which will be adapted to the social, cultural and economic situation of the country and to available health services.
Asunto(s)
Hipotiroidismo Congénito/epidemiología , Bocio/epidemiología , Yodo/deficiencia , Adolescente , Adulto , Chad/epidemiología , Niño , Métodos Epidemiológicos , Femenino , Humanos , Yodo/orina , Masculino , PrevalenciaRESUMEN
In N'Djamena, capital of Chad, measles vaccination coverage of 12-23-month-old children fell from 61% in 1990 to 15% in 1993. A community survey of measles after an outbreak in 1993 showed that among children < 5 years of age, the mean monthly attack rate was 37 per 1,000 (95% CI, 32-43) and the mean case fatality rate was 7.4%. Measles incidence was highest (77/1,000/month) in children aged 9-11 months and fell among children > 3 years of age. Incidence rates were high (56/1,000/month) among 6-8-month-old children, but only 3 deaths occurred in this age group. Measles vaccine efficacy, estimated by comparing attack rates in unvaccinated and vaccinated children, was 71% (95% CI, 59-80%). Extrapolation of the results to the city population indicated that an estimated 19,000 cases and > 1,000 measles-associated deaths occurred in 1993. This preventable morbidity and mortality, in a city where coverage was formerly among the highest in Africa, shows the need for sustained global commitment to preventive health care.
Asunto(s)
Brotes de Enfermedades , Vacuna Antisarampión , Sarampión/epidemiología , Sarampión/prevención & control , Distribución por Edad , Chad/epidemiología , Preescolar , Femenino , Humanos , Incidencia , Lactante , Masculino , Vigilancia de la Población , Factores de Riesgo , Estaciones del Año , Salud Urbana , Vacunación/estadística & datos numéricos , Vacunación/tendenciasRESUMEN
A concurrent prospective study was conducted in Rwanda to compare the immunogenicity and safety of live, attenuated measles vaccine in ill and well children. Five hundred and eighteen children aged 8 to 19 months were selected from children attending the acute care and immunization services of two clinics. Two hundred and sixty-seven ill children and 251 well children were enrolled and examined. Serological tests were performed on blood samples obtained before and 40 days after measles immunization. Among the 208 ill children and 215 well children who were seronegative at baseline and had unequivocal follow-up serological results, seroconversion rates were 81% and 80%, respectively. Side effects were modest and were equally frequent in the two study groups (15.4% among ill children versus 15.1% among well children). These results support a change in measles immunization policy in developing countries with respect to immunization of children with acute illnesses. Such a change would make a great contribution to decreasing the enormous burden of measles in the developing world through increased immunization coverage.