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Publications (10)79.37 Total impact

  • M. Elizabeth Halloran · Preziosi M.P · Haitao Chu
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    ABSTRACT: Epidemiologists have used secondary attack rates (SARs) to estimate the protective effects of vaccination since the 1930s. SARs can also be used to estimate the effect of vaccination on reducing infectiousness in breakthrough cases. The conventional SAR approach has been to pool the denominators and numerators across transmission units, then to use a confidence interval for a simple relative risk. We demonstrate appropriate model-based methods to estimate vaccine efficacy (VE) from SARs using generalized estimating equations taking correlation within transmission units into account. The model-based procedures require transformation of the parameter estimates to the SAR scale to obtain vaccine efficacy estimates. Appropriate confidence intervals are then based on the bootstrap, with resampling done by transmission unit. We show that the usual confidence intervals are too narrow. We estimated the effect of pertussis vaccination on person-to-person transmission. The results show that pertussis vaccination reduces the ability of a breakthrough clinical case to produce other clinical cases. The methods can be used in evaluating VE for susceptibility and infectiousness from SARs in other infectious diseases.
    Journal of the American Statistical Association 02/2003; 98(1):38-46. DOI:10.1198/016214503388619076 · 2.11 Impact Factor
  • M.-P. Preziosi
    American Journal of Epidemiology 01/2002; 155(10):891-896. DOI:10.1093/aje/155.10.891 · 4.98 Impact Factor
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    V Delaunay · J F Etard · M P Préziosi · A Marra · F Simondon
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    ABSTRACT: In spite of an improving trend, childhood mortality in rural sub-Saharan Africa remains high and has recently risen in some countries. The factors associated with the long-term decline in childhood mortality are poorly known, due to a lack of data. A Senegalese rural population has been under demographic surveillance since 1963. Infant and under-5 mortality rates were calculated for different periods to generate a long-term trend in childhood mortality. Evolution of age and seasonal patterns of mortality were observed. During the observation period (1963-1999), infant and under-5 mortality rates decreased from 223 per thousand to 80 per thousand and 485 per thousand to 213 per thousand , respectively, with a constant annual rate of decline in the probability of dying since the 1960s (-3.7% and -3.1%, respectively). The age pattern of the under-5 mortality changed drastically, with a large decrease in the death rate between 6 and 24 months of age (from 321 per thousand to 87 per thousand ). This change took place during the 1970s. The seasonal variation, characterized by a greater proportion of deaths during the rainy season, was very marked during the 1960s, then decreased during the 1980s but it has tended to increase again in the 1990s, particularly among children 1-4 years old. This study confirms the long-term trend of decrease in child mortality in rural West Africa. Historical knowledge on healthcare developments suggests that immunizations have contributed to the decrease and the change in the age pattern. The re-emergence of malaria seems the most likely explanation for the recent rebound in seasonal variation. Attention to immunization and malaria should continue to be a priority.
    International Journal of Epidemiology 01/2002; 30(6):1286-93; discussion 1294-5. · 9.20 Impact Factor
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    ABSTRACT: Following a study in Senegal (1990-1995) in which the relative efficacy of a diphtheria-tetanus-acellular pertussis vaccine (DTaP) was compared with that of a diphtheria-tetanus-whole-cell pertussis vaccine in children given a simultaneous injection of Bacille Calmette-Guérin (BCG) vaccine, this subsequent study was conducted to evaluate the possible adjuvant effect of the BCG vaccine on acellular pertussis vaccine components. A second objective was to compare the immunogenicity of these components when administered in accordance with a 2-4-6-month (spaced) schedule or an accelerated 2-3-4-month schedule. In all, 390 healthy Senegalese infants were randomly divided into three groups of 130 infants. Antibodies to acellular pertussis components were measured in serum samples obtained within 2 days of the first DTaP dose and 1 month after the third dose. BCG vaccine, given simultaneously with the DTaP vaccine, did not influence the immunogenicity of the acellular pertussis vaccine components when compared with separate administration of the two vaccines. Infants immunised according to a 2-4-6-month schedule had a significantly higher immune response than those immunised according to a 2-3-4-month schedule with respect to the response to pertussis toxoid assessed by seroneutralisation on Chinese hamster ovary cells (P<0.0001). These results suggest that BCG and DTaP vaccines can be given simultaneously without interference or enhancement and that more optimal immunogenicity is achieved with an extended than with an accelerated schedule.
    European Journal of Clinical Microbiology 02/1999; 18(1):23-9. DOI:10.1007/s100960050221 · 2.67 Impact Factor
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    ABSTRACT: Over 12 years, from 1984 to 1995, we conducted a prospective study of overall and malaria specific mortality among three rural populations in the Sahel, savanna and forest areas of Senegal. The emergence of chloroquine resistance has been associated with a dramatic increase in malaria mortality in each of the studied populations. After the emergence of chloroquine resistance, the risk of malaria death among children 0-9 years old in the three populations was multiplied by 2.1, 2.5 and 5.5, respectively. This is the first study to document malaria mortality at the community level in Africa before and after the emergence of chloroquine resistance. Findings suggest that the spread of chloroquine resistance has had a dramatic impact on the level of malaria mortality in most epidemiological contexts in tropical Africa.
    Comptes Rendus de l Académie des Sciences - Series III - Sciences de la Vie 09/1998; 321(8):689-97. DOI:10.1016/S0764-4469(98)80009-7
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    François Simondon · Isabelle Iteman · Marie Pierre Preziosi · Abdoulaye Yam · Nicole Guiso
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    ABSTRACT: The enzyme-linked immunosorbent assay is widely employed for the serological diagnosis of pertussis. It is generally concluded that a significant increase in specific immunoglobulin G (IgG) or IgA against the pertussis toxin (PT) or against filamentous hemagglutinin (FHA) in paired sera correlates with Bordetella pertussis infection. However, this type of diagnosis of pertussis has mainly been applied to unvaccinated children, with timely sampling of acute- and convalescent-phase sera. In current practice and in epidemiological studies, such criteria are not always fulfilled. The aim of this study was to analyze the significance of decreases in IgG antibody titers against PT and FHA between paired sera observed in suspected cases of pertussis infection. Serological results from paired sera were available for 460 children experiencing at least 8 days of cough. An anti-PT IgG decrease was observed in 25% of the children, more frequently than the anti-FHA IgG decrease. Fourteen percent of the serologic decreases were observed in children with culture-confirmed infection, and 59% of the decreases were observed in children with confirmation criteria according to World Health Organization recommendations. Most of the decreases were observed when serum samples were collected according to a standard recommended schedule. Serologic decreases were observed more frequently among vaccinated children than among unvaccinated children. This difference, which was highly significant (P < 0.00001), was explained by the different kinetics of the antibody responses between vaccinated and unvaccinated children. The importance of the antibody response for the evaluation of vaccine efficacy, namely a bias toward higher absolute vaccine efficacy when this response is not taken into account, is discussed. This study supports an earlier recommendation that a significant decrease in PT or FHA should be added to the diagnostic criteria for pertussis.
    Clinical and Diagnostic Laboratory Immunology 03/1998; 5(2). · 2.51 Impact Factor
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    ABSTRACT: A randomized, double-blind trial comparing a diphtheria-tetanus-acellular pertussis vaccine (DTaP) (pertussis toxoid and filamentous hemagglutinin) with a whole-cell vaccine (DTwP) was conducted. A case-contact study was nested in the trial to estimate absolute efficacy. From 1990 through 1994, 4181 children were randomized to receive one of the vaccines at 2, 4, and 6 months. Severe adverse events were monitored weekly during two visits after vaccination. Fewer serious adverse events were observed after DTaP. Surveillance for cough illnesses persisting more than 7 days, in children under 15 years of age, was made by weekly home visits. Examining physicians, blind to vaccination status, took samples for culture and serologic testing. Pertussis was defined as 21 or more days of cough confirmed by culture, serology, or contact with a culture-confirmed person. Beginning 28 days after the third vaccine dose, the overall ratio of pertussis incidence in the DTaP group relative to the DTwP group (RRac/wc) was 1.54 (95% CI, 1.23-1.93). In children younger than 18 months of age, RRac/wc was 1.16 (95% CI, 0.77-1.73) and 1.76 (95% CI, 1.33-2.33) in children older than 18 months, which suggests a shorter duration of protection with the acellular vaccine (P = 0.090). Absolute efficacy estimates derived from the case-contact study confirmed the lower protection afforded by the acellular vaccine compared with the whole-cell vaccine: 31% (95% CI, 7-49) versus 55% against the protocol case definition, and 85% (95% CI, 66-93) versus 96% for the more severe WHO case definition. Although vaccination with DTaP provided a lower degree of protection than the highly effective DTwP, this difference was less prominent before 18 months of age, the customary age for a fourth dose. The safer DTaP vaccine may prove a valuable substitute for whole-cell vaccines when used in a schedule that includes a booster-dose.
    Vaccine 11/1997; 15(15):1606-12. DOI:10.1016/S0264-410X(97)00100-X · 3.49 Impact Factor
  • New England Journal of Medicine 02/1997; 336(5):370-3. DOI:10.1056/NEJM199701303360511 · 54.42 Impact Factor
  • M P Preziosi · M Ndiaye · A Coll-Seck · F Simondon
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    ABSTRACT: In the Senegal pertussis trial, common adverse reactions were actively monitored during the pilot phase II study, while the frequency of severe adverse reactions was monitored as a secondary objective within the phase III efficacy trial. Since the trial was conducted in Niakhar, an area in rural West Africa under intensive surveillance, the safety monitoring during the study was incorporated within the general surveillance system. This was a two-step procedure: detection of a potential reaction by a field worker, followed by confirmation report by a physician. The frequency of severe reactions was low among both pertussis vaccine groups, receiving either the two-component acellular vaccine or the whole-cell vaccine currently used in the Senegal Expanded Programme on immunisation. Among severe reactions, only persistent crying was found to be at a significantly higher rate in the whole-cell group. Common adverse reactions were more frequent in the whole-cell group.
    Developments in biological standardization 02/1997; 89:91-7.