Reduced childhood mortality after standard measles vaccination at 4-8 months compared with 9-11 months of age

Abstract

Objective: To evaluate the impact on mortality of standard Schwarz measles immunisation before 9 months of age.

Design: Children vaccinated in 1980-3 at 4-5, 6-8, and 9-11 months of age were followed to migration, death, or the age of 5 years.

Setting: One urban district and nine villages in two rural areas of Guinea-Bissau.

Subject: 307 children vaccinated at 4-8 months and 256 at 9-11 months.

Main outcome measures: Mortality from 9 months to 5 years of age for children immunised at 4-5, 6-8, and 9-11 months.

Results: Mortality was significantly lower in children vaccinated at 6-8 months than at 9-11 months (mortality ratio = 0.63, (95% confidence interval 0.41 to 0.97), p = 0.047). As vaccination was provided in semiannual or annual campaigns it is unlikely that age at vaccination reflected a selection bias. The trend was the same in all three study areas. Improved survival after early immunisation was not related to better protection against measles infection. With a Cox multivariate regression model to adjust for age, sex, season at risk, season at birth, measles infection, and region, children vaccinated at 4-8 months had a mortality ratio of 0.61 (0.40 to 0.92, p = 0.020) compared with children vaccinated at 9-11 months. Reimmunised children tended to have lower mortality than children who received only one vaccine (0.59 (0.28 to 1.27, p = 0.176)).

Conclusion: Standard measles vaccination before 9 months is not associated with higher childhood mortality than is the currently recommended strategy of immunising from 9 months, and it may reduce mortality. This has implications for measles immunisation strategy in developing countries.

PIP: In 1980-83, health workers followed children living in urban Bandim district or in the rural regions of Oio and Quinhamel in Guinea-Bissau to death, migration, or to age 5 to compare mortality of 307 of the children who were vaccinated against measles at 4-8 months with the mortality of the remaining 256 children who were vaccinated against measles at 9-11 months. Health workers conducted the vaccination campaigns on an annual or semiannual basis, so age at vaccination probably did not pose a selection bias. Children vaccinated at 6-8 months were significantly less likely to die than those vaccinated at 9-11 months (mortality ratio [6-8 months/9-11 months] = .63; p = .047). Child survival was much higher in the 6-8 month group than the 9-11 month group in all 3 areas. When researchers adjusted for age, sex, season at risk, season at birth, measles infection, and region, child survival was significantly better in children vaccinated against measles at 4-8 months than it was at 9-11 months (mortality ratio = .61; p = .02). Children who were reimmunized died less often than those who were immunized only once (mortality ratio - .59), but the difference was not significant. These findings suggested that measles vaccination before 9 months of age plus reimmunization result in better childhood survival than does 1 measles vaccination at 9-11 months of age (the current recommended strategy for measles immunization). The researchers stress the need for more research on longterm survival after measles immunization at different ages and reimmunization.