Divergent mortality for male and female recipients of low-titer and high-titer measles vaccines in rural Senegal

Abstract

The female/male mortality ratio among unimmunized children and children vaccinated with standard or high-titer measles vaccines was examined for all children born in the period 1985-1991 in a rural area of Senegal. The female/male mortality ratio from 9 months to 5 years of age for unvaccinated children was 0.94 (95% confidence interval (CI) 0.75-1.19), significantly different from the ratio of 0.64 (95% CI 0.48-0.85) for recipients of the Schwarz standard measles vaccine (p = 0.040). In the 4-year period, where high-titer measles vaccines were used in the study area, the female/male mortality ratio was 1.33 (95% CI 1.00-1.78) for recipients of high-titer Edmonston-Zagreb or Schwarz vaccines compared with 0.67 (95% CI 0.42-1.07) for recipients of the Schwarz standard vaccine (p = 0.013). Hence, the Schwarz standard and high-titer measles vaccines have divergent sex-specific effects on mortality throughout childhood. Further studies of the underlying mechanisms are needed.

PIP: The female/male mortality ratio among unimmunized children and children vaccinated with the Schwarz standard or Edmonston-Zagreb high-titer measles vaccine was examined for all children born in period 1985-1991. The cohort included all children born between February 1, 1987, and January 31, 1989. From 1983 to 1987, annual censuses (and after 1987, weekly surveillance visits) of the Sereer population of Niakhar yielded data on migration, marriages, births, mortality, vaccinations, breast feedings, and infections. Mortality was examined from 9 months, the recommended age for immunization with the Schwarz standard measles vaccine. Children were followed until death, migration, 5 years of age, or the annual census in February 1992. At 5 months of age (or when they were 10 months old), children were randomized to receive a placebo or a high-titer dose of Edmonston-Zagreb or Schwartz standard measles vaccine. All 2467 children born in the period were included, of whom 2118 lived in the study area after the age of 9 months. 11% of the Schwarz standard-vaccinated children received their vaccination after 12 months of age (92 and 810). After 9 months of age, there were 29 boys and 26 girls who had measles among unvaccinated (22 boys, 21 girls), Schwarz standard-vaccinated (1 boy, 2 girls), and high-titer-vaccinated children (6 boys, 3 girls). The female/male mortality ratio from 9 months to 5 years of age for unvaccinated children was 0.94, significantly different from the ratio of 0.64 for recipients of the Schwarz standard measles vaccine (p = 0.040). In the 4-year period, the female/male mortality ratio was 1.33 for recipients of high-titer Edmonston-Zagreb or Schwarz vaccines, compared with 0.67 for recipients of the Schwarz standard vaccine (p = 0.013). The Schwarz standard and high-titer measles vaccines had divergent sex-specific effects on mortality throughout childhood to be taken into consideration in future studies of measles vaccination.