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Mass Vaccination (mass + vaccination)

Distribution by Scientific Domains

Medical Sciences	60%

Selected Abstracts

Effect of Small-World Networks on Epidemic Propagation and Intervention

GEOGRAPHICAL ANALYSIS, Issue 3 2009
Zengwang Xu
The small-world network, characterized by special structural properties of high connectivity and clustering, is one of the highlights in recent advances in network science and has the potential to model a variety of social contact networks. In an attempt to better understand how these structural properties of small-world networks affect epidemic propagation and intervention, this article uses an agent-based approach to investigate the interplay between an epidemic process and its underlying network structure. Small-world networks are derived from a network "rewiring" process, which readjusts edges in a completely regular two-dimensional network by different rewiring probabilities (0,1) to produce a spectrum of modified networks on which an agent-based simulation of epidemic propagation can be conducted. A comparison of simulated epidemics discloses the effect of small-world networks on epidemic propagation as well as the effectiveness of different intervention strategies, including mass vaccination, acquaintance vaccination, targeted vaccination, and contact tracing. Epidemics taking place on small-world networks tend to reach large-scale epidemic peaks within a short time period. Among the four intervention strategies tested, only one strategy,the targeted vaccination,proves to be effective for containing epidemics, a finding supported by a simulation of the severe acute respiratory syndrome epidemic in a large-scale realistic social contact network in Portland, OR. Las redes de mundo de pequeño (,small-world networks'), caracterizadas por sus propiedades estructurales especiales de alta conectividad y aglomeración (,clustering') son uno de los ejemplos más destacados de los avances más recientes de la ciencia de redes, y tiene el potencial de modelar una gran variedad de redes sociales de contacto. En un intento de comprender mejor como estas propiedades estructurales de redes ,small-world' afectan la propagación e intervención de epidemias, el estudio presente emplea un enfoque basado en modelos multi-agente (,agent based') para investigar la interacción entre el proceso epidémico y la estructura de redes en la que estan integrados. Las redes de mundo pequeño se derivan del proceso de recableado (,rewiring') el cual reajusta los límites en una red 2-D de acuerdo a varias probabilidades de reconexión (0-1) para producir un abanico de posibles de redes modificadas sobre los cuales se condujo una simulación multi-agente de la propagación de la epidemia. El efecto de las redes ,small world' y de las diferentes estrategias de intervención (por ejemplo, diferentes estrategias de vacunación) son evidenciadas mediante la comparación entre varias simulaciones de la epidemia. Las epidemias que ocurren en redes de tipo ,small-world' tienden a alcanzar picos de gran escala epidémica en un corto periodo de tiempo. Entre las estrategias evaluadas, sólo una ,vacunación dirigida a una población objetivo (,targeted vaccination')- demostró ser efectiva en la contención de la epidemia. Dicho resultado se obtuvo vía la simulación de la epidemia de SRAS (Síndrome Respiratorio Agudo Severo ,SARS') realiada en Portland, Oregon (EEUU). [source]

Epidemiology of varicella-zoster virus in England and Wales

JOURNAL OF MEDICAL VIROLOGY, Issue S1 2003
M. Brisson
Abstract Many countries are studying currently the possibility of mass vaccination against varicella. The objective of this study was to provide a complete picture of the pre-vaccine epidemiology of the Varicella-Zoster Virus in England and Wales to aid in the design of immunisation programs. Population-based data including general practitioner sentinel surveillance, hospitalisation data, and death certificates from England and Wales were analysed. The average incidence rates for varicella and zoster between 1991 and 2000 were 1,291 and 373 per 100,000 years, respectively. Overall hospitalisation rates were equal for varicella and zoster (4.5 vs. 4.4 hospitalisation per 100,000 population) with 5 and 8%, respectively, having underlying immunosuppressive conditions. The age-specific proportion of cases hospitalised and length of stay were similar between the two diseases. However, the overall burden of disease is considerably higher for zoster. The number of inpatient days and case-fatality due to zoster are roughly 4 to 6 times greater than for varicella (11 vs. 3 days and 25 vs. 4 deaths per 100,000 case). These results provide base-line estimates should mass varicella vaccination be introduced in England and Wales. J. Med. Virol. 70:S9,S14, 2003. © 2003 Wiley-Liss, Inc. [source]

Differences in hepatitis A seroprevalence among geographical regions in Turkey: a need for regional vaccination recommendations

JOURNAL OF VIRAL HEPATITIS, Issue 2008
M. Ceyhan
Summary., Hepatitis A is a worldwide vaccine-preventable infection. Recommendation of vaccination depends on the endemicity of the disease. The World Health Organization recommends universal hepatitis A vaccination in intermediate areas; however, there is no need of mass vaccination in high and low endemicity regions. Therefore, most of the countries are using a vaccination policy according to the endemicity characteristic representing the whole of the country. The endemicity of this infection varies due to sanitary and hygiene conditions and socioeconomic differences among the countries and in various regions of the same country. A sample of 1173 persons between the age of 0 and 91 years from nine randomly selected medical centres from five different geographical centres of Turkey were tested for the level of anti-hepatitis A virus (anti-HAV) immunoglobulin-G antibodies using an enzyme-linked immunosorbent assay. The overall prevalence of anti-HAV antibodies was 64.4% (1142/1173). While the rate of sero-positivity was over 80% in the 5,9 age group and more than 90% after 14 years of age in south-eastern and eastern regions, it was lower than 50% at the age of 5,9 years in central and western regions and remains under 80% in those areas. We conclude that the differences observed in HAV sero-positivity among various geographical regions in Turkey support a universal HAV immunization policy for children currently living in regions of intermediate endemicity. [source]

Multiple sclerosis incidence in the era of measles-mumps-rubella mass vaccinations

ACTA NEUROLOGICA SCANDINAVICA, Issue 5 2009
C. Ahlgren
Background,,, Viral childhood infections may be involved in the multiple sclerosis (MS) pathogenesis. Following national Swedish vaccination programs, measles sharply declined in the 1970s, and measles, mumps, and rubella were virtually eliminated in cohorts born from 1981. Objectives,,, To examine whether the vaccination induced reduction in these infections influences the MS incidence. In addition, the public health aspect justified an early evaluation of beneficial as well as harmful effects of mass vaccinations. Materials and methods,,, From an incidence material of 534 MS patients, born 1959,1990, we selected one unvaccinated cohort and four cohorts, each corresponding to a vaccination program (MS patients = 251). Results,,, With the ability to detect a decrease by 30,35%, and an increase by 37,48% in the MS incidence in the first three cohorts, we found no vaccination related MS incidence changes. The background MS incidence showed a significant gradual age dependent increase. Conclusions,,, While the present follow-up provided limited power in the last cohort, there is no evidence as yet that the radical decline in three viral infections influenced the MS incidence. However, the increasing background MS incidence of unknown cause may have concealed a reduction in MS risk associated with mass vaccinations. [source]