Academic journal article Bulletin of the World Health Organization

Measles Immunization Research: A Review

Academic journal article Bulletin of the World Health Organization

Measles Immunization Research: A Review

Article excerpt

Introduction

The WHO Expanded Programme on Immunization (EPI) estimates that 1.6 million children die from measles each year in developing countries (excluding China), (a) making it the biggest killer among the six EPI target diseases. Other workers have estimated that measles is responsible for 0.9-1.5 million deaths per year in developing countries (1, 2). Globally, around 70 million cases occur annually. Opinion has varied not only as to real death toll from measles but also about the value of immunization against the disease.

Since, on the one hand, measles mortality is usually associated with both poor living conditions and malnutrition, it has often been suggested that the disease mostly kills children who, in any case, are likely to die from other infections (3, 4). In consequence, measles immunization may increase child survival only to a limited extent, if at all, because prevention of deaths from measles through immunization may result in children surviving, only to die from other causes. On the other hand, many children are weakened and become malnourished after measles infection, so that the disease may lead to excess delayed mortality (5, 6). If so, the number of children who survive because of being immunized should exceed the number of acute measles deaths that are prevented.

These contrasting hypotheses have implications for the emphasis given to measles control within primary health care programmes and have prompted us to undertake this review of the available data on the case fatality rates for measles and the mortality impact of measles infection and measles immunization.

Mortality from measles

Magnitude of deaths from acute measles

Official estimates of the number of deaths from acute measles infection may be too low. EPI calculates that the case fatality rate (CFR) for acute infection among persons of all ages in developing countries is 2-4%, that the CFR throughout Africa and Asia is 3-4%, and that it is 2% in the majority of countries in South America. It is very difficult, however, to estimate the rate in many of these areas because registration of cases is unreliable. Data from longitudinal community studies indicate that the CFR ranges from 34% to 0% in rural Africa (7-11, 20, 21), (b) from 21% to 6% in urban Africa (4, 12, 13), and from 5% to 0% in other studies (14-19). With few exceptions (16, 18, 19, 21), CFRs from these longitudinal community studies are higher than EPI estimates, at least during the initial stages of an investigation (20, 21). In particular, for Africa, the difference between official estimates and the observed CFRs is considerable. Notably, for West and Central Africa, mortality from measles in the community may well be two or three times higher than the estimated 3%.

Delayed impact on mortality and morbidity

Available data strongly suggest that children who have previously been infected with measles have a significant excess morbidity and mortality compared with community controls. If measles should continue to have an effect on a child after the period of acute infection, it may have a considerably greater influence on mortality than is usually assumed (5). Unfortunately very few studies have examined the impact of previous measles infection on later morbidity and mortality, and in those that have, the comparison between previous cases and controls is associated with serious methodological problems.

Hull et al. reported an outbreak of measles in a village in the Gambia which they re-visited 3 and 9 months later to assess the impact of the disease (22, 23). The results indicated that for children who had contracted measles, the excess risk of dying after the acute infection was highly significantly greater than that of community controls. Deaths were distributed throughout the 8-month follow-up period. The excess mortality seemed to be particularly high for the children under 1 year of age. …

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