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PubMedDate not supplied

Economic evaluation of vaccination programs: the impact of herd-immunity.

The unique characteristic of vaccination is that it not only reduces the incidence of disease in those immunized but also indirectly protects nonvaccinated susceptibles against infection (produces herd-immunity). The bulk of economic evaluations of vaccination programs continue to use models that cannot take into account the indirect effects produced by herd-immunity. Here, the authors illustrate the importance of incorporating herd-immunity externalities when assessing the cost-effectiveness of vaccination progams. To do this, they compare 2 methods of estimating the benefits of routine mass vaccination: one that includes herd-immunity (dynamic approach) and one that does not (static approach). Finally, they use the results to clarify a number of misconceptions that are common in the literature concerning herd-immunity and dynamical effects produced by models.

Adolescent↗
PubMed2005

Scaling properties of childhood infectious diseases epidemics before and after mass vaccination in Canada.

The goal of this paper is to analyse the scaling properties of childhood infectious disease time-series data. We present a scaling analysis of the distribution of epidemic sizes of measles, rubella, pertussis, and mumps outbreaks in Canada. This application provides a new approach in assessing infectious disease dynamics in a large vaccinated population. An inverse power-law (IPL) distribution function has been fit to the time series of epidemic sizes, and the results assessed against an exponential benchmark model. We have found that the rubella epidemic size distribution and that of measles in highly vaccinated periods follow an IPL. The IPL suggests the presence of a scale-invariant network for these diseases as a result of the heterogeneity of the individual contact rates. By contrast, it was found that pertussis and mumps were characterized by a uniform network of transmission of the exponential type, which suggests homogeneity in the contact rate or, more likely, boiled down heterogeneity by large intermixing in the population. We conclude that the topology of the network of infectious contacts depends on the disease type and its infection rate. It also appears that the socio-demographic structure of the population may play a part (e.g. pattern of contacts according to age) in the structuring of the topology of the network. The findings suggest that there is relevant information hidden in the variation of the common contagious disease time-series data, and that this information can have a bearing on the strategy of vaccination programs.

Canada↗
PubMedDate not supplied

The integration of family planning and childhood immunization services in Togo.

Improvements in the constellation of services in the African context are largely addressed through attaining better measures of service integration, which can be achieved through improved referral across categories of health programs. The use of an unobtrusive referral message that linked family planning and the Expanded Program of Immunizations (EPI) services was tested in an operations research study in Togo. The introduction of the referral message was accompanied by an 18-percent increase in awareness of available family planning services and an increase in the average monthly number of new family planning clients of 54 percent. These positive results indicate that the use of referral can have a significant and dramatic impact on family planning services in a relatively short time. In Togo, no evidence existed of a negative impact on EPI services, and a majority of the EPI providers reported satisfaction with the effect of the referral message at the close of the study.

Child Health Services↗
PubMed1984

The future of measles in highly immunized populations. A modeling approach.

Little is known about how an intensive measles elimination program changes the overall immune status of the population. A computer model was created to study the effect of the measles elimination program in the United States on the number of susceptibles in the population. The simulation reveals that in the prevaccine era, approximately 10.6% of the population was susceptible to measles, most of whom were children less than 10 years of age. With the institution of the measles immunization program, the proportion of susceptibles in the population fell to 3.1% from 1978 through 1981, but then began to rise by approximately 0.1% per year to reach about 10.9% in the year 2050. The susceptibles at this time were distributed evenly throughout all age groups. The model did not consider the potential effect of waning immunity. The results of this study suggest that measles elimination in the United States has been achieved by an effective immunization program aimed at young susceptibles combined with a highly, naturally immunized adult population. However, despite short-term success in eliminating the disease, long-range projections demonstrate that the proportion of susceptibles in the year 2050 may be greater than in the prevaccine era. Present vaccine technology and public health policy must be altered to deal with this eventuality.

Adolescent↗
PubMed2003

Preparation and characterization of group A meningococcal capsular polysaccharide conjugates and evaluation of their immunogenicity in mice.

Epidemic and endemic meningitis caused by group A Neisseria meningitidis remains a problem in sub-Saharan Africa. Although group A meningococcal capsular polysaccharide (GAMP) vaccine confers immunity at all ages, the improved immunogenicity of a conjugate and its compatibility with the World Health Organization's Extended Program on Immunization offers advantages over GAMP alone. Conjugates of GAMP bound to bovine serum albumin (BSA) were synthesized, characterized, and evaluated for their immunogenicities in mice. Two methods, involving adipic acid dihydrazide (ADH) as a linker, were used. First, ADH was bound to GAMP activated with cyanogen bromide (CNBr) or with 1-cyano-4(dimethylamino)-pyridinium tetrafluoroborate (CDAP) to form GAMP(CNBr)AH and GAMP(CDAP)AH. These derivatives were bound to BSA by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) to form GAMP(CNBr)AH-BSA and GAMP(CDAP)AH-BSA. Second, ADH was bound to BSA with EDC to form AHBSA. AHBSA was bound to activated GAMP to form GAMP(CNBr)-AHBSA and GAMP(CDAP)-AHBSA. The yield of GAMP(CDAP)-AHBSA (35 to 40%) was higher than those of the other conjugates (5 to 20%). GAMP conjugates elicited immunoglobulin G (IgG) anti-GAMP in all mice after three injections of 2.5 or 5.0 microg of GAMP: the geometric mean (GM) was highest in recipients of GAMP(CDAP)-AHBSA (11.40 enzyme-linked immunosorbent assay units). Although the difference was not statistically significant, the 5.0- microg dose elicited a higher GM IgG anti-GAMP than the 2.5- microg dose. Low levels of anti-GAMP were elicited by GAMP alone. GAMP(CDAP)-AHBSA elicited bactericidal activity roughly proportional to the level of IgG anti-GAMP.

Adipates↗
PubMed2000

Vaccine procurement and self-sufficiency in developing countries.

This paper discusses the movement toward self-sufficiency in vaccine supply in developing countries (and countries in transition to new economic and political systems) and explains special supply concerns about vaccine as a product class. It traces some history of donor support and programmes aimed at self-financing, then continues with a discussion about self-sufficiency in terms of institutional capacity building. A number of deficiencies commonly found in vaccine procurement and supply in low- and middle-income countries are characterized, and institutional strengthening with procurement technical assistance is described. The paper also provides information about a vaccine procurement manual being developed by the United States Agency for International Development (USAID) and the World Health Organization (WHO) for use in this environment. Two brief case studies are included to illustrate the spectrum of existing capabilities and different approaches to technical assistance aimed at developing or improving vaccine procurement capability. In conclusion, the paper discusses the special nature of vaccine and issues surrounding potential integration and decentralization of vaccine supply systems as part of health sector reform.

Developing Countries↗