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Excess mortality after early exposure to measles
P Aaby1, M Andersen, K Knudsen
1Department of Epidemiology, Statens Seruminstitut, Copenhagen, Denmark.
Insights
Exposure to measles before six months of age significantly increases childhood mortality in Guinea-Bissau. This early measles exposure led to higher mortality ratios in both urban and rural settings, suggesting a greater impact of measles immunization than previously assumed.
Area of Science:
- Pediatrics
- Infectious Diseases
- Epidemiology
Background:
- Measles infection in early infancy can have severe, long-term health consequences.
- Understanding the full impact of measles exposure is crucial for public health interventions.
Purpose of the Study:
- To investigate the impact of measles exposure before 6 months of age on survival up to 5 years of age.
- To compare mortality rates between measles-exposed children and controls in urban and rural Guinea-Bissau.
Main Methods:
- A comparative survival analysis was conducted in urban (Bandim) and rural (Quinhamel) areas of Guinea-Bissau.
- Mortality ratios (MR) were calculated using matched pair and unpaired Cox' regression analyses.
- Statistical models were adjusted for background variables including sex, measles infection status, age at exposure, and vaccination status.
Main Results:
- In the urban area, exposed children had a significantly higher mortality ratio (MR=3.80) compared to controls up to age 5.
- Higher mortality trends persisted even after 2 years of age (MR=7.96).
- The rural area showed an even higher mortality ratio for exposed children (MR=11.39).
Conclusions:
- Early-life measles exposure substantially increases cumulative mortality in children.
- The findings suggest that measles immunization may play a more critical role in reducing overall childhood mortality than currently estimated.
- Subclinical measles infections may contribute to excess mortality, underscoring the importance of widespread vaccination programs.
Abstract:
The impact of exposure to measles before 6 months of age has been investigated by comparing survival to 5 years of age for exposed children and controls in an urban (Bandim) and a rural (Quinhamel) area of Guinea-Bissau. In Bandim, cumulative mortality from time of exposure to age 5 years was 34.4% among exposed children and 9.3% among controls. In a matched pair analysis, exposed children had a mortality ratio (MR) of 3.80 (95% confidence interval [CI]: 1.42-10.18) compared with controls. In an unpaired analysis using Cox' regression model to standardize for background variables (sex, measles infection, age at exposure, exposure from own household, measles vaccination), there was little change in the MR (3.84, CI: 1.55-9.48). Even after 2 years of age, the exposed children tended to have higher mortality (MR = 7.96, CI: 0.98-64.74). In the rural area, the MR between exposed children and controls was 11.39 (CI: 1.42-91.51). Limited serological data suggest that at least some of the exposed had subclinical measles. In the urban area, where two studies of early exposure have been carried out, excess mortality among exposed children corresponds to 40% and 52%, respectively, of the acute measles mortality. Since these deaths would not be associated with measles in a study of protection against death after vaccination, measles immunization may have a much greater effect on childhood mortality than has previously been assumed.