Jette Bukh

Measles vaccination and reduction in child mortality: A community study from Guinea-Bissau

Earlier studies have suggested that general measles vaccination programmes should not be made a priority in developing countries because the presumably malnourished children saved from measles are likely to die from something else. Recent community studies indicate, however, that malnutrition is not the cause of high measles mortality. In an urban community in Guinea-Bissau, child mortality has been registered for a period of 3 years; 1 year before and 2 years after the introduction of a general measles vaccination program. In the years following the introduction of measles vaccination, mortality for children aged 6 to 35 months has significantly diminished. Though this is not a controlled study of vaccinated and unvaccinated children, much of the reduced mortality can apparently be attributed to the protective effect of measles vaccination. Children with a history of earlier measles infection had a significantly higher mortality rate than children vaccinated against measles. Rather than being a mechanism of natural selection taking the weakest children, measles apparently aggravates the condition of many children, leading to delayed excess mortality. In areas where the case fatality rate is high, vaccination against measles should be made an indispensable part of primary health care.

High measles mortality in infancy related to intensity of exposure

In a West African urban community, measles infection in infants was examined over 5 years (1979-1983). In the age group 0 to 11 months, measles mortality was higher among secondary cases (infected in the house) than among index cases (infected outside the house), and the proportion of secondary cases was significantly higher for this age group than for older children. Intensive exposure related to the social pattern of disease transmission may be important in explaining the high infant mortality observed with measles in developing countries. Mortality during the first 12 months of life increased with age, presumably because of the decrease of maternally derived measles antibodies. In children younger than 6 months of age, who are usually considered to be protected by maternal antibody, intensive exposure may lead to infection, as demonstrated by a high level of measles-specific antibodies in some children exposed to an older sibling with measles. The aim of public health policies should be to change conditions of exposure.

Determinants of measles mortality in a rural area of Guinea-Bissau: crowding, age, and malnutrition.

Malnutrition has been considered the major determinant of high measles mortality. Data from a rural area of Guinea-Bissau suggests that overcrowding and age may be more important as determinants than nutritional status. Case fatality rate was significantly higher in houses with several cases than in homes with only a single case. Measles vaccination may contribute to increased survival rates by limiting the number of infections raising the mean age of attack and by impeding clustering of cases. 66% of the cases occured during the dry season. The case fatality rate (CFR) for children under 5 years of age was 33.7% and for children 5 years and older 6.6%. The highest CFR was observed for children in the age group 0-11 and 12-23 months of age 46.7% and 52.4% respectively.

INCREASED PERINATAL MORTALITY AMONG CHILDREN OF MOTHERS EXPOSED TO MEASLES DURING PREGNANCY

A survey done after a severe epidemic of measles in an urban area of Guinea-Bissau has shown that children born to women exposed to measles during pregnancy had a perinatal mortality rate of 15%, compared with only 4% for other children in the community (OR = 4.2; 95% CI 2.1-8.5). None of the women had clinical evidence of measles. Adjusting for background variables, logistic regression analysis showed no tendency towards reduced risk of perinatal mortality among children of women exposed during pregnancy relative to controls. Both stillbirth and early neonatal mortality rates were increased. A similar tendency was found in a rural epidemic (OR = 9.5; 95% CI 2.6-35.1). Exposure during any trimester of fetal life increased the rate of perinatal mortality. The results suggest that exposure to measles virus or some concomitantly transmitted pathogen may contribute to the high perinatal mortality risk found in many developing countries. The possible long-term health consequences of exposure to measles virus should be considered when assessing the value of measles control programmes.

Decline in measles mortality: nutrition, age at infection, or exposure?

The mortality from measles was studied in an urban area of Guinea-Bissau one year before and five years after the introduction of a vaccination programme. The years after the introduction of immunisation saw a decline in mortality among unvaccinated children with measles. This decline occurred despite a lower age at infection and an increasing prevalence of malnourished children. State of nutrition (weight for age) did not affect the outcome of measles infection. The incidence of isolated cases, however, increased in the period after the introduction of measles vaccination. As mortality was lower among these cases, diminished clustering explained some of the reduction in mortality. Comparison between the urban district and a rural area inhabited by the same ethnic group showed a lower age at infection, less clustering of cases, and lower case fatality ratios in the urban area. Endemic transmission of measles in urban districts leads to less clustering of cases, which may help explain the usually lower case fatality ratios in these areas. As measles vaccination increases herd immunity and diminishes clustering of cases, it may reduce mortality even among unvaccinated children who contract the disease.

Introduction of measles into a highly immunised West African community: the role of health care institutions.

In an urban area of Guinea-Bissau, where more than 80% of the children have been vaccinated, measles continues to be a major cause of child mortality. Compared with the period before the introduction of vaccination, more cases occur outside the community, while more cases within the district are now guests and newcomers. Half of the new introductions of measles into the community and 30% of the measles deaths can be traced back to the paediatric ward. Contact with health care institutions plays an important role in the transmission of measles, particularly among the youngest children. This consequence of health care may be avoidable, however, since several studies suggest that sick children can be vaccinated safely and effectively.

Humoral immunity in measles infection: A critical factor?

Cell-mediated immunity is generally regarded as the essential factor in recovery from measles infection. In other viral infections humoral immunity has been considered a critical factor when antibody titres were correlated with outcome or when serum therapy proved protective. A review of available studies of severe-to-fatal cases of measles infection having non-neurological symptoms indicate that the antibody response is depressed in virtually all cases. The current view of immune globulin being an ineffective therapeutic agent is based on treatment of measles encephalitis; in fact, the least effect should be expected among encephalitis cases since some already have antibodies from the onset of symptoms. Larger examinations of measles with other than neurological symptoms suggest that immune globulin has a beneficial impact on the clinical course of infection. There are indications that hyperimmune globulin increases the efficacy of this form of treatment. Since measles is still a major cause of hospitalization and mortality, further studies of the therapeutic effect of specific immune globulin are warranted. From our current knowledge, both the humoral and cell-mediated immunity seem to be critical factors in recovery from measles infection.

Increased perinatal mortality among children of mothers exposed to measles during pregnancy

A survey done after a severe epidemic of measles in an urban area of Guinea-Bissau has shown that children born to women exposed to measles during pregnancy had a perinatal mortality rate of 15%, compared with only 4% for other children in the community (OR=4·2; 95% CI 2·1-8·5). None of the women had clinical evidence of measles. Adjusting for background variables, logistic regression analysis showed no tendency towards reduced risk of perinatal mortality among children of women exposed during pregnancy relative to controls. Both stillbirth and early neonatal mortality rates were increased. A similar tendency was found in a rural epidemic (OR=9·5; 95% CI 2·6-35·1). Exposure during any trimester of fetal life increased the rate of perinatal mortality. The results suggest that exposure to measles virus or some concomitantly transmitted pathogen may contribute to the high perinatal mortality risk found in many developing countries. The possible long-term health consequences of exposure to measles virus should be considered when assessing the value of measles control programmes.