In December 1997, 170 hemorrhagic fever-associated deaths were reported in Carissa District, Kenya. Laboratory testing identified evidence of acute Rift Valley fever virus (RVFV). Of the 171 persons enrolled in a cross-sectional study, 31(18%) were anti-RVFV immunoglobulin (Ig) M positive. An age-adjusted IgM antibody prevalence of 14% was estimated for the district. We estimate approximately 27,500 infections occurred in Garissa District, making this the largest recorded outbreak of RVFV in East Africa. In multivariate analysis, contact with sheep body fluids and sheltering livestock in one’s home were significantly associated with infection. Direct contact with animals, particularly contact with sheep body fluids, was the most important modifiable risk factor for RVFV infection. Public education during epizootics may reduce human illness and deaths associated with future outbreaks.
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.
SUMMARYIn N'Djamena, capital of Chad, measles vaccination coverage of 12-23-monthold 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 1000 (95 % CI, 32-43) and the mean case fatality rate was 74%. Measles incidence was highest (77/1000/month) in children aged 9-11 months and fell among children > 3 years of age. Incidence rates were high (56/1000/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 %
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.
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