ArticlesFirst 5 years of measles elimination in southern Africa: 1996–2000
Introduction
Measles is the most contagious disease known to man. Globally, although national immunisation programmes are estimated to prevent 80 million cases and 4·5 million deaths due to measles yearly, it is estimated that more than 30 million cases and 0·9 million deaths still occur every year.1 Approximately half of these deaths occur in Africa.2 Measles is the leading cause of death in children in Africa, even though it is preventable by a vaccine that is currently in widespread use in developing countries. The measles vaccine is highly effective and safe; the major reason for the remaining measles disease burden is failure to vaccinate, not vaccine failure.3
In 1989 and 1990, respectively, the World Health Assembly4 and the World Summit for Children5 set specific goals for the reduction in measles morbidity by 90% and of measles mortality by 95%, as major milestones towards measles eradication in the long-term. Measles elimination is considered technically feasible6, 7 because: current vaccines are sufficiently efficacious; measles is primarily a disease of man—there is no non-human reservoir; there is no carrier state and very few symptom-free cases; and measles immunity acquired by vaccination or natural disease is of very long, possibly life-long, duration.
Strategies currently recommended by WHO to achieve measles elimination include: routine vaccination coverage of 95% or more, with one dose of measles vaccine administered at 9 months of age to immunise most children; implementation of a national catch-up measles vaccination campaign in children aged 9 months to 14 years with coverage of 90% or more, to reduce the residual number of susceptible children; implementation of periodic national follow-up measles campaigns in children aged 9 months to 59 months with coverage of 90% or more, and frequency every 3–4 years depending upon the rate of accumulation of new susceptible children in the population; and the establishment of case-based measles surveillance with laboratory confirmation to monitor and assess impact.
Routine vaccination coverage with one dose of standard measles vaccine at 9 months of age is associated with a vaccine efficacy of approximately 85%.8
A mass vaccination activity lends itself better to reaching children that were not reached by the routine vaccination programme, to immunise measles susceptibles in the population. Therefore, it is more effective to provide a second opportunity for measles vaccination through a single nationwide mass measles catch-up campaign. This campaign should be done among an epidemiologically determined target group, usually children 9 months to 14 years of age regardless of vaccination or disease history.9 Experience in the WHO Americas Region shows that if catch-up campaign coverage of more than 90% can be achieved, measles transmission will be significantly reduced or interrupted.10
Unvaccinated children and children born after the measles catch-up campaign who do not respond to vaccination at 9 months of age will contribute to the gradual accumulation of measles susceptible individuals in the population. This new accumulation is then reduced with periodic mass follow-up campaigns. The timing of follow-up campaigns necessarily depends on coverage achieved during both the routine programme and the catch-up campaign. To achieve maximum effect on measles transmission, all catch-up and follow-up vaccination campaigns should be done in the low season of measles transmission, usually the drier winter months.
During the decade preceding the launching of measles elimination initiatives in the seven southern African countries of Botswana, Lesotho, Malawi, Namibia, South Africa, Swaziland, and Zimbabwe, average routine vaccination coverage with one dose of measles vaccine administered at 9 months of age of approximately 80% was achieved and sustained. This stable high routine coverage had a substantial effect on measles epidemiology.11 Measles morbidity declined substantially, the interval between epidemics lengthened, the average age of measles cases increased, the proportion of primary vaccine failures among measles cases rose, with measles mortality reduced to very low levels.
With these epidemiological pre-conditions in place, and building upon experience gained in implementing the vaccination campaigns and case-based surveillance strategies associated with the polio eradication initiative, political commitment and operational support was obtained for launching measles elimination in the seven countries, in accordance with WHO/African Regional Office recommendations, and with advocacy and technical assistance provided by the WHO Southern African Expanded Programme on Immunisation (EPI) Unit.
The national prevalence rates of HIV-1 infection in southern African countries are among the highest in the world. At present, roughly a third of fertile-age adults in southern Africa are HIV-positive, although prevalance is often much higher in certain high-risk groups such as sex workers, soldiers, and long-distance drivers. From available data, we can therefore assume that up to 10% of newborns in southern African countries become HIV infected perinatally or through breastfeeding.
Section snippets
Country information
Catch-up vaccination campaigns in each country were planned and implemented by national Ministries of Health, with technical assistance from WHO/African Regional Office. The South African government funded its measles campaign in full; in the other countries, campaigns received primary financial support from Ministries of Health, the UK Department for International Development (DFID), UNICEF, and the US Centers for Disease Control and Prevention (CDC). Particular emphasis was placed on the
Results
A total of nearly 24 million children were vaccinated during the catch-up measles campaigns. Overall, reported coverage was 91% in the seven countries that have completed their campaigns (table 1). Coverage was not independently verified. Namibia and South Africa implemented mopping-up vaccination activities in selected districts where initial coverage of less than 70% was achieved. No deaths or cases with persisting sequelae associated with vaccination were reported. In Zimbabwe, four children
Discussion
To sustain the gains achieved through the measles elimination initiative in the long-term, the seven southern African countries are continuing to implement WHO-recommended measles elimination strategies. Firstly, the Ministries of Health in the seven countries are committed to identifying and implementing innovative operational and promotional steps to raise routine vaccination coverage to more than 95% in each district, including the elimination of missed opportunities for vaccination, to
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Measles Vaccines
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2016, International Journal of Infectious DiseasesCitation Excerpt :Past studies have shown a decreased serological response to measles vaccination among HIV-infected adults, waning immunity following vaccination in HIV-positive infants and children, and lower protective immunity to measles among infants born to HIV-infected mothers.25–28 Although HIV infection is associated with lower vaccine effectiveness29 and an increased risk of measles outbreaks,30 the contribution of the HIV pandemic to measles control and elimination in Sub-Saharan Africa appears to be minimal.31–33 The present findings mirror those of a Kenyan measles seroprevalence study in HIV-positive and negative adults, which also found no differences between these two populations.34