Global Vaccination Coverage Research Articles

Strengthening routine immunization systems to improve global vaccination coverage.

Global coverage with the third dose of diphtheria-tetanus-pertussis vaccine among children under 1 year of age stagnated at ∼ 83-84% during 2008-13. Annual World Health Organization and UNICEF-derived national vaccination coverage estimates. Incomplete vaccination is associated with poor socioeconomic status, lower education, non-use of maternal-child health services, living in conflict-affected areas, missed immunization opportunities and cancelled vaccination sessions. Vaccination platforms must expand to include older ages including the second year of life. Immunization programmes, including eradication and elimination initiatives such as those for polio and measles, must integrate within the broader health system. The Global Vaccine Action Plan (GVAP) 2011-20 is a framework for strengthening immunization systems, emphasizing country ownership, shared responsibility, equity, integration, sustainability and innovation. Immunization programmes should identify, monitor and evaluate gaps and interventions within the GVAP framework.

Next generation vaccines: single-dose encapsulated vaccines for improved global immunisation coverage and efficacy.

Vaccination is considered the most successful health intervention; yet incomplete immunisation coverage continues to risk outbreaks of vaccine preventable diseases worldwide. Vaccination coverage improvement through a single-dose prime-boost technology would revolutionise modern vaccinology, impacting on disease prevalence, significantly benefiting health care and lowering economic burden of disease. Over the past 30 years, there have been efforts to develop a single-dose delayed release vaccine technology that could replace the repeated prime-boost immunisations required for many current vaccines. Biocompatible polymers have been employed to encapsulate model vaccines for delayed delivery in vivo, using either continuous or pulsed release. Biomaterial considerations, safety aspects, particle characteristics and immunological aspects of this approach are discussed in detail. Despite many studies showing the feasibility of vaccine encapsulation for single-dose prime-boost administration, none have been translated into convincing utility in animal models or human trials. Further development of the encapsulation technology, through optimising the particle composition, formulation, antigen loading efficacy and stability, could lead to the application of this important approach in vaccine deployment. If successful, this would provide a solution to better global vaccination coverage through a reduction in the number of immunisations needed to achieve protection against infectious diseases. This review provides an overview of single-dose vaccination in the context of today's vaccine needs and is derived from a body of literature that has not been reviewed for over a decade.

Maternal Education and Immunization Status Among Children in Kenya.

Child morbidity and mortality due to infectious diseases continues to be a major threat and public health concern worldwide. Although global vaccination coverage reached 90 % for diphtheria, tetanus and pertussis (DTP3) across 129 countries, Kenya and other sub-Saharan countries continue to experience under-vaccination. The purpose of this study was to examine the association between maternal education and child immunization (12-23 months) in Kenya. This study used retrospective cross-sectional data from the 2008-2009 Kenya Demographic and Health Survey for women aged 15-49, who had children aged 12-23 months, and who answered questions about vaccination in the survey (n = 1,707). The majority of the children had received vaccinations, with 77 % for poliomyelitis, 74 % for measles, 94 % for tuberculosis, and 91 % for diphtheria, whooping cough (pertussis), and tetanus. After adjusting for other covariates, women with primary, secondary, and college/university education were between 2.21 (p < 0.01) and 9.10 (p < 0.001) times more likely to immunize their children than those who had less than a primary education. Maternal education is clearly crucial in ensuring good health outcomes among children, and integrating immunization knowledge with maternal and child health services is imperative. More research is needed to identify factors influencing immunization decisions among less-educated women in Kenya.

Overview of global, regional, and national routine vaccination coverage trends and growth patterns from 1980 to 2009: implications for vaccine-preventable disease eradication and elimination initiatives.

Review of the historical growth in annual vaccination coverage across countries and regions can better inform decision makers' development of future goals and strategies to improve routine vaccination services. Using the World Health Organization (WHO) and the United Nations Children's Fund estimates of annual national third dose of diphtheria-tetanus-pertussis-containing vaccine (DTP3) and third dose of polio vaccine (POL3) coverage for 1980-2009, we calculated the mean absolute annual rate of change in national DTP3 coverage among all countries (globally) and among countries within each WHO region, as well as the number of years taken by each region to reach specific regional coverage levels. Last, we assessed differences in mean absolute annual rate of change in DTP3 coverage, stratified by baseline level of DTP3 coverage. During the 1980s, global DTP3 coverage increased a mean of 5.3 percentage points/year. Annual rate of change decreased to 0.5 percentage points/year in the 1990s and then increased to 0.9 percentage points/year during the 2000s. Mean annual rate of change in coverage across all countries was highest (9.2 percentage points) when national coverage levels were 26%-30% and lowest (-0.9 percentage points) when national coverage levels were 96%-100%. Regional differences existed as both WHO South-East Asia Region and WHO African Region countries experienced mean negative DTP3 coverage growth at lower coverage levels (81%-85%) than other regions. The regions that have achieved 95% DTP3 coverage (Americas, Western Pacific, and European) took 25-29 years to reach that level from a level of 50% DTP3 coverage. POL3 coverage change trends were similar to described DTP3 coverage change trends. Mean national coverage growth patterns across all regions are nonlinear as coverage levels increase. Saturation points of mean 0 percentage-point growth in annual coverage varies by region and require further investigation. The achievement of >90% routine coverage is observed to take decades, which has implications for disease eradication and elimination initiatives.

Global immunization through the lens of development.

Supporting global immunization programs is a profound way to control disease and improve the lives of many, particularly in the developing world. In 1974, the World Health Organization (WHO) created the Expanded Programme on Immunization (EPI), a worldwide effort mobilized to help countries increase immunization coverage of basic childhood vaccines—diphtheria, measles, pertussis, polio, tetanus, and tuberculosis—using the third dose of diphtheria, tetanus, and pertussis (DTP3) as a measure of progress. Building on the historical success of smallpox eradication, the WHO sought to increase global vaccination coverage (which was <5% in 1974) among children younger than one year of age. However, one-fifth of the world's children, especially those who live in low-income countries, are not fully vaccinated with these traditional vaccines during their first year of life.1 The Global Vaccine Action Plan (GVAP) for 2011–2020 has established immunization coverage targets of at least 90% DTP3 coverage nationally and at least 80% DTP3 coverage in every district.2 Countries can take a variety of actions to attain these targets, depending on their needs and the current status of their health system and immunization program. This year, on the 40th anniversary of EPI, through the collective work of many partners, we are witnessing a time of unprecedented support and commitment to ending preventable child and maternal deaths within a generation, a top priority of the U.S. Agency for International Development (USAID). In this Decade of Vaccines,2 we join global efforts to extend the full benefits of immunization to all people, regardless of where they are born, who they are, or where they live. And USAID continues its long-standing partnership with the U.S. Department of Health and Human Services (HHS) and other actors on the global stage. Our work as a development agency contributes to global efforts outlined in this report by the National Vaccine Advisory Committee (NVAC) Global Immunizations Working Group, “Enhancing the Work of the Department of Health and Human Services National Vaccine Program in Global Immunization: Recommendations of the National Vaccine Advisory Committee.”3 The challenges and recommendations in the report highlight holistic approaches to technical and financial investments in health as well as increased coordination among the partnership of actors. We support these efforts, particularly through a developmental lens, emphasizing support to national governments toward investing in health, immunization programs, and human and institutional resources.

Heterologous prime-boost immunization with live attenuated B. pertussis BPZE1 followed by acellular pertussis vaccine in mice

Pertussis is a severe and life-threatening infectious disease. Two successive generations of vaccines have strongly reduced its incidence over the last 70 years. However, despite excellent global vaccine coverage, it is still not under control and constitutes today the most frequent vaccine-preventable childhood disease. New vaccination approaches are therefore needed. Here, we provide preclinical proof of concept for a heterologous prime-boost strategy, using the live attenuated Bordetella pertussis vaccine candidate BPZE1 to prime infant and neonatal mice intranasally and a currently available acellular pertussis vaccine (aPV) as a booster. Intranasal vaccination with BPZE1 provided strong protection against challenge in neonatal mice, which could be boosted with a single dose of aPV. Furthermore, BPZE1 priming induced a strong Th1/Th17 response, which was maintained after repeated aPV administrations, in contrast to non-primed mice, in which aPV administrations resulted in Th2 skewing. In addition to T cell responses, intranasal administration of BPZE1 to infant or neonatal mice also primed antibody responses to B. pertussis antigens, with a strong preference of the IgG2a over the IgG1 isotypes, which was not seen in non-primed animals. Finally, neonatal BPZE1 priming strongly enhanced aPV-induced protection against B. pertussis challenge. These results lend support for a heterologous prime-boost strategy to control pertussis by using BPZE1 early in life and considering the current aPV administrations as booster vaccinations, thereby bridging the gap from birth to the first aPV immunizations and avoiding aPV-mediated Th2 skewing. A first-in-man clinical trial on BPZE1 has recently been successfully completed, which provides hope that these findings may be translated into human applications in the future.

Langerin negative dendritic cells promote potent CD8 + T-cell priming by skin delivery of live adenovirus vaccine microneedle arrays

Stabilization of virus protein structure and nucleic acid integrity is challenging yet essential to preserve the transcriptional competence of live recombinant viral vaccine vectors in the absence of a cold chain. When coupled with needle-free skin delivery, such a platform would address an unmet need in global vaccine coverage against HIV and other global pathogens. Herein, we show that a simple dissolvable microneedle array (MA) delivery system preserves the immunogenicity of vaccines encoded by live recombinant human adenovirus type 5 (rAdHu5). Specifically, dried rAdHu5 MA immunization induced CD8(+) T-cell expansion and multifunctional cytokine responses equipotent with conventional injectable routes of immunization. Intravital imaging demonstrated MA cargo distributed both in the epidermis and dermis, with acquisition by CD11c(+) dendritic cells (DCs) in the dermis. The MA immunizing properties were attributable to CD11c(+) MHCII(hi) CD8α(neg) epithelial cell adhesion molecule (EpCAM(neg)) CD11b(+) langerin (Lang; CD207)(neg) DCs, but neither Langerhans cells nor Lang(+) DCs were required for CD8(+) T-cell priming. This study demonstrates an important technical advance for viral vaccine vectors progressing to the clinic and provides insights into the mechanism of CD8(+) T-cell priming by live rAdHu5 MAs.

Global measles vaccine coverage improving, but still less than ideal

Global measles vaccine coverage improving, but still less than ideal

디프테리아 백신의 진화와 물리화학적, 분자생물학적, 면역학적 지식의 진보에 따른 새로운 백신의 개발에 관한 고찰연구

This review article provides an overview of the evolution of diphtheria vaccine, its value and its future. Diphtheria is an infectious illness caused by diphtheria toxin produced by pathogenic strains of Corynebacterium diphtheriae. It is characterized by a sore throat with membrane formation due to local tissue necrosis, which can lead to fatal airway obstruction; neural and cardiac damage are other common complications. Diphtheria vaccine was first brought to market in the 1920s, following the discovery that diphtheria toxin can be detoxified using formalin. However, conventional formalin-inactivated toxoid vaccines have some fundamental limitations. Innovative technologies and approaches with the potential to overcome these limitations are discussed in this paper. These include genetic inactivation of diphtheria toxoid, innovative vaccine delivery systems, new adjuvants (both TLRindependent and TLR-dependent adjuvants), and heat- and freeze-stable agents, as well as novel platforms for producing improved conventional vaccine, DNA vaccine, transcutaneous (microneedle-mediated) vaccine, oral vaccine and edible vaccine expressed in transgenic plants. These innovations target improvements in vaccine quality (efficacy, safety, stability and consistency), ease of use and/or thermal stability. Their successful development and use should help to increase global diphtheria vaccine coverage.

Assessment of national strategies for control of high-pathogenicity avian influenza and lowpathogenicity notifiable avian influenza in poultry, with emphasis on vaccines and vaccination

Twenty-nine distinct epizootics of high-pathogenicity avian influenza (HPAI) have occurred since 1959. The H5N1 HPAI panzootic affecting Asia, Africa and Eastern Europe has been the largest among these, affecting poultry and/or wild birds in 63 countries. A stamping-out programme achieved eradication in 24 of these epizootics (and is close to achieving eradication in the current H5N2 epizootic in South African ostriches), but vaccination was added to the control programmes in four epizootics when stamping out alone was not effective. During the 2002 to 2010 period, more than 113 billion doses of avian influenza (AI) vaccine were used in at-risk national poultry populations of over 131 billion birds. At two to three doses per bird for the 15 vaccinating countries, the average national vaccination coverage rate was 41.9% and the global AI vaccine coverage rate was 10.9% for all poultry. The highest national coverage rate was nearly 100% for poultry in Hong Kong and the lowest national coverage was less than 0.01% for poultry in Israel and The Netherlands. Inactivated AI vaccines accounted for 95.5% and live recombinant virus vaccines for 4.5% of the vaccines used. Most of these vaccines were used in the H5N1 HPAI panzootic, with more than 99% employed in the People's Republic of China, Egypt, Indonesia and Vietnam. Implementation of vaccination in these four countries occurred after H5N1 HPAI became enzootic in domestic poultry and vaccination did not result in the enzootic infections. Vaccine usage prevented clinical disease and mortality in chickens, and maintained rural livelihoods and food security during HPAI outbreaks. Low-pathogenicity notifiable avian influenza (LPNAI) became reportable to the World Organisation for Animal Health in 2006 because some H5 and H7 low-pathogenicity avian influenza (LPAI) viruses have the potential to mutate to HPAI viruses. Fewer outbreaks of LPNAI have been reported than of HPAI and only six countries used vaccine in control programmes, accounting for 8.1% of the total H5/H7 AI vaccine usage, as compared to 91.9% of the vaccine used against HPAI. Of the six countries that have used vaccine to control LPNAI, Mexico, Guatemala, El Salvador and Italy have been the biggest users. In countries with enzootic HPAI and LPNAI, development and implementation of exit strategies has been difficult.

Implementation and impact of a meningococcal C conjugate vaccination program in 13- to 25-year-old individuals in Galicia, Spain

BackgroundIn response to increased case numbers of meningococcal group C disease, catch-up vaccination strategies have been shown to be successful. This paper describes the results of a repeat vaccination program in Galicia, Spain, and the strategy used for it.Methods and resultsThree vaccination waves were performed: first, in 1996/1997 with a meningococcal group A and C polysaccharide vaccine in individuals aged 18 months to 19 years; second, in 2000 with a conjugate serogroup C polysaccharide vaccine in children born since 1993 and all children and adolescents up to 19 years not previously vaccinated; third, a campaign in 2006 that became necessary because of the development of a new Neisseria strain and an increase in both the incidence and lethality of meningococcal C disease. The conjugate vaccine de-O-acetylated group C meningococcal polysaccharide coupled to tetanus toxoid was used (GCMP-TT; brand name, NeisVac-C). Results: Applying a strategy based on model calculations derived from the UK setting and focusing on a population aged 13–25 years, including students, employees of companies, and underage individuals, a total of 286,000 subjects were vaccinated, resulting in global vaccination coverage of 82.2% (all age groups over 74%). Only 17 adverse events in 17 individuals were reported, which all were mild. Incidence of meningococcal disease serogroup C by season was reduced from 0.84 cases per 100,000 in 2004/05 to 0.76 cases per 100,000 in 2005/2006 to 0.18/100,000 in 2007/08. In parallel, mortality was also decreased from 8 cases during 2005/06 (0.29 per 100,000) to 1 case in 2007/2008 (0.03 per 100,000). No cases of breakthrough disease occurred in the vaccinated population.ConclusionIn Galicia, a series of vaccination campaigns, particularly focusing on high-risk groups, has shown high effectiveness, with a marked reduction in the disease incidence in the vaccination cohort accompanied by a relevant reduction in the overall population.

Cost-effectiveness of novel vaccines for tuberculosis control: a decision analysis study.

BackgroundThe development of a successful new tuberculosis (TB) vaccine would circumvent many limitations of current diagnostic and treatment practices. However, vaccine development is complex and costly. We aimed to assess the potential cost effectiveness of novel vaccines for TB control in a sub-Saharan African country - Zambia - relative to the existing strategy of directly observed treatment, short course (DOTS) and current level of bacille Calmette-Guérin (BCG) vaccination coverage.MethodsWe conducted a decision analysis model-based simulation from the societal perspective, with a 3% discount rate and all costs expressed in 2007 US dollars. Health outcomes and costs were projected over a 30-year period, for persons born in Zambia (population 11,478,000 in 2005) in year 1. Initial development costs for single vaccination and prime-boost strategies were prorated to the Zambian share (0.398%) of global BCG vaccine coverage for newborns. Main outcome measures were TB-related morbidity, mortality, and costs over a range of potential scenarios for vaccine efficacy.ResultsRelative to the status quo strategy, a BCG replacement vaccine administered at birth, with 70% efficacy in preventing rapid progression to TB disease after initial infection, is estimated to avert 932 TB cases and 422 TB-related deaths (prevention of 199 cases/100,000 vaccinated, and 90 deaths/100,000 vaccinated). This would result in estimated net savings of $3.6 million over 30 years for 468,073 Zambians born in year 1 of the simulation. The addition of a booster at age 10 results in estimated savings of $5.6 million compared to the status quo, averting 1,863 TB cases and 1,011 TB-related deaths (prevention of 398 cases/100,000 vaccinated, and of 216 deaths/100,000 vaccinated). With vaccination at birth alone, net savings would be realized within 1 year, whereas the prime-boost strategy would require an additional 5 years to realize savings, reflecting a greater initial development cost.ConclusionsInvestment in an improved TB vaccine is predicted to result in considerable cost savings, as well as a reduction in TB morbidity and TB-related mortality, when added to existing control strategies. For a vaccine with waning efficacy, a prime-boost strategy is more cost-effective in the long term.

Childhood vaccination in informal urban settlements in Nairobi, Kenya: Who gets vaccinated?

BackgroundRecent trends in global vaccination coverage have shown increases with most countries reaching 90% DTP3 coverage in 2008, although pockets of undervaccination continue to persist in parts of sub-Saharan Africa particularly in the urban slums. The objectives of this study were to determine the vaccination status of children aged between 12-23 months living in two slums of Nairobi and to identify the risk factors associated with incomplete vaccination.MethodsThe study was carried out as part of a longitudinal Maternal and Child Health study undertaken in Korogocho and Viwandani slums of Nairobi. These slums host the Nairobi Urban Health and Demographic Surveillance System (NUHDSS) run by the African Population and Health Research Centre (APHRC). All women from the NUHDSS area who gave birth since September 2006 were enrolled in the project and administered a questionnaire which asked about the vaccination history of their children. For the purpose of this study, we used data from 1848 children aged 12-23 months who were expected to have received all the WHO-recommended vaccinations. The vaccination details were collected during the first visit about four months after birth with follow-up visits repeated thereafter at four month intervals. Full vaccination was defined as receiving all the basic childhood vaccinations by the end of 24 months of life, whereas up-to-date (UTD) vaccination referred to receipt of BCG, OPV 1-3, DTP 1-3, and measles vaccinations within the first 12 months of life. All vaccination data were obtained from vaccination cards which were sighted during the household visit as well as by recall from mothers. Multivariate models were used to identify the risk factors associated with incomplete vaccination.ResultsMeasles coverage was substantially lower than that for the other vaccines when determined using only vaccination cards or in addition to maternal recall. Up-to-date (UTD) coverage with all vaccinations at 12 months was 41.3% and 51.8% with and without the birth dose of OPV, respectively. Full vaccination coverage (57.5%) was higher than up-to-date coverage (51.8%) at 12 months overall, and in both slum settlements, using data from cards. Multivariate analysis showed that household assets and expenditure, ethnicity, place of delivery, mother's level of education, age and parity were all predictors of full vaccination among children living in the slums.ConclusionsThe findings show the extent to which children resident in slums are underserved with vaccination and indicate that service delivery of immunization services in the urban slums needs to be reassessed to ensure that all children are reached.

Global immunization: status, progress, challenges and future.

Vaccines have made a major contribution to public health, including the eradication of one deadly disease, small pox, and the near eradication of another, poliomyelitis.Through the introduction of new vaccines, such as those against rotavirus and pneumococcal diseases, and with further improvements in coverage, vaccination can significantly contribute to the achievement of the health-related United Nations Millennium Development Goals.The Global Immunization Vision and Strategy (GIVS) was developed by WHO and UNICEF as a framework for strengthening national immunization programmes and protect as many people as possible against more diseases by expanding the reach of immunization, including new vaccines, to every eligible person.This paper briefly reviews global progress and challenges with respect to public vaccination programmes.The most striking recent achievement has been that of reduction of global measles mortality from an estimated 750,000 deaths in 2000 down to 197,000 in 2007. Global vaccination coverage trends continued to be positive. In 2007 most regions reached more than 80% of their target populations with three doses of DPT containing vaccines. However, the coverage remains well short of the 2010 goal on 90% coverage, particularly in the WHO region of Africa (estimated coverage 74%), and South-East Asia, (estimated coverage 69%). Elements that have contributed to the gain in immunization coverage include national multi-year planning, district-level planning and monitoring, re-establishment of outreach services and the establishment of national budget lines for immunization services strengthening.Remaining challenges include the need to: develop and implement strategies for reaching the difficult to reach; support evidence-based decisions to prioritize new vaccines for introduction; strengthening immunization systems to deliver new vaccines; expand vaccination to include older age groups; scale up vaccine preventable disease surveillance; improve quality of immunization coverage monitoring and use the data to improve programme performance; and explore financing options for reaching the GIVS goals, particularly in lower-middle income countries.Although introduction of new vaccines is important,this should not be at the expense of sustaining existing immunization activities. Instead the introduction of new vaccine introduction should be viewed as an opportunity to strengthen immunization systems, increase vaccine coverage and reduce inequities of access to immunization services.

The unfinished measles immunization agenda.

Despite achieving and sustaining global measles vaccination coverage of about 80% over the past decade, worldwide measles remains the fifth leading cause of mortality among children aged <5 years. In May 2002, the United Nations Special Session on Children endorsed the goal of reducing measles deaths by half by 2005. Countries and World Health Organization (WHO) regions that adopted aggressive measles control or elimination strategies have shown excellent results. In 2001, countries in the Americas reported an all time low of 537 confirmed measles cases. Substantial progress in measles control has also been achieved in the WHO Western Pacific Region, in seven southern African countries, and in selected countries in WHO European, Eastern Mediterranean, and Southeast Asian regions. The ongoing measles disease burden and availability of safe and effective measles mortality reduction strategies make a compelling case to complete the unfinished agenda of measles immunization.

Measles: a disease that has to be eradicated.

The incidence of measles is on the decline but it still claims the lives of one million children annually worldwide. The devastating effects of the disease on the health and nutrition of children in developing countries and its high mortality are well documented. The rapid decay of maternal antibodies in infants in developing countries results in early susceptibility to the disease and hence the general recommendation to vaccinate at the age of 9 months. Sustained international efforts have raised global vaccination coverage rates to around 80% at which level it has remained static. Many countries in the western hemisphere have eliminated the disease by adopting aggressive strategies, which include one-off 'catch-up' mass campaigns to vaccinate all children aged 1-14 years, 'mop-up' campaigns targeting children who were missed during the 'catch-up' campaign, efficient routine vaccination services capable of reaching 90% of infants, strong surveillance activities, prompt outbreak response, and 'follow-up' campaigns every 2-4 years which target 1-4-year-old children. This success story coupled with the fact that measles has many biological features favouring eradication, and considering that it is a severe and lethal disease still prevailing in many areas, calls for immediate international adoption of eradication goals within a specified period of time.

The miracle of vaccination.

Among all medical procedures, vaccination ranks at the forefront in lives saved and disabling illnesses prevented. Jenner's first experiments with vaccination, 200 years ago, culminated in the eradication of smallpox at the conclusion of a ten–year World Health Organization programme begun in 1967. Two million lives were saved each year and tens of thousand of blindness cases. In 1974, the smallpox campaign was expanded to include six additional vaccines (poliomyelitis, measles, diphtheria, tetanus, pertussis and tuberculosis). By 1990, global vaccination coverage had risen from less than 5% to 80% poliomyelitis was eradicated from the Americas; and a global eradication campaign was launched. Prospects for more dramatic achievements are bright. Research and development in new vaccines is gaining momentum. More than 150 new vaccines are now in human testing and vaccines against such as malaria, dengue fever and AIDS can be foreseen. Challenges remain in assuring adequate research funds for diseases of the developing world and in supplying needed quantities of assured, high quality vaccines. However, the threat of new and emerging infections and the fact that vaccines are the front line of defense reinforce the need for further strengthening of vaccine research, development and production. * Commemorative bicentenary lecture delivered on 15 May 1996 in the Royal Society.

Towards eradication of measles virus: global progress and strategy evaluation

Despite an increase in global measles vaccine coverage from under 20% in 1980 to around 80% in 1990, measles remains a major cause of morbidity and mortality world-wide. This paper addresses a number of issues relating to efforts to control measles, namely, (i) at the global level, how might we assess the impact of measles vaccination on the incidence of infection and associated disease, and, (ii), at the strategic level, how can we utilise an understanding of the transmission dynamics of childhood viral infections to aid the design of optimal immunisation programmes? Based on WHO vaccine coverage data, and organising countries according to similarities in demographic and epidemiological parameters, an age-structured model of measles transmission is used to capture the non-linear dynamics of infection and mass vaccination and to generate projections of the impact of measles immunization world-wide. The results provide a crude indication of the percentage reduction in measles cases by year 2000 (compared with no immunization) and suggest an approximately 70% reduction in cases over all ages, and 77% reduction in cases under 5 years (where there is the greatest risk of case fatality); these suggest that WHO targets for 1995 are unlikely to be achieved. In the second part of the paper, examples are given to illustrate the usefulness of a modelling approach in evaluating measles immunization policy. The introduction of MMR vaccine in the UK in 1988 has resulted in measles incidence falling to an all time low and attention has turned to the requirements of elimination. A realistic age structured model, validated using extensive serological data, is used to compare the merits of single or two dose strategies. Based upon recent estimates of vaccine efficacy (90%) and coverage (92% by end of second year of life) it is suggested that a two-dose policy with a pre-school second dose given irrespective of vaccine history is required to prevent the build up of susceptibles to epidemic proportions in the longer term. In a second example, prompted by the success of the campaign approach to polio and measles elimination in Central and South America, simple models are used to explore and quantify the process by which pulse vaccination programmes (i.e. repeated application across a wide age range) act to control transmission.