A comparison of vaccine efficacy and mortality during routine use of high-titre Edmonston-Zagreb and Schwarz standard measles vaccines in rural Senegal

Abstract

Vaccine efficacy and mortality in successive cohorts of children who routinely received either Edmonston-Zagreb high-titre (EZ-HT) or Schwarz standard (SW-STD) measles vaccines have been examined in a rural area of Senegal. The 2 vaccines were equally protective against measles infection (vaccination efficacy: EZ-HT 94%; SW-STD 93%). Children who did not attend a scheduled session to receive measles vaccine had a higher mortality rate between 9 months and 2 years of age than did children receiving either EZ-HT (mortality ratio [MR] = 1 · 81, 95% confidence interval [CI] 1 · 06–3 · 08) or SW-STD measles vaccine (MR = l · 74, 95% CI 0 · 95–3 · 21). Children of either sex vaccinated with EZ-HT had lower mortality than their equivalents who had not received any measles vaccine. There was no difference in overall mortality between recipients of EZ-HT and SW-STD (MR = 0 · 96,95% CI 0 · 70–1 · 30). Using a Cox regression analysis to adjust for sex, age and significant background factors (season and death of mother), mortality rates tended to be lower for male recipients of EZ-HT than for boys receiving SW-STD (MR = 0 · 73, 95% CI 0 · 50–1 · 11) and higher for girls receiving EZ-HT than for girls receiving SW-STD (MR = 1 · 30, 95% CI 0 · 81–2 · 09) (test of interaction between sex and vaccine, P = 0 · 067). The tendency to reduced survival benefit for girls following receipt of high-titre measles vaccines substantiated observations from randomized trials in Guinea-Bissau, Senegal and Haiti. Existing data provide little support for the notion that high-titre vaccine is deleterious but it may not have the same beneficial effects as standard-titre measles vaccine.