Measles control in Kinshasa, Zaire improved with high coverage and use of medium titre Edmonston Zagreb vaccine at age 6 months.

BACKGROUND: To improve measles control in Kinshasa, Zaire, a project to increase vaccine coverage was begun in 1988, and in 1989, the city vaccination programme changed measles vaccination policy from Schwartz vaccine at age 9 months to medium titre Edmonston Zagreb (EZ) vaccine at age 6 months. We report the impact of the programme on measles incidence and mortality. METHODS: Data on vaccine coverage were obtained from cluster sample surveys conducted every 1-2 years and from routine reports of vaccine doses administered. Data on measles incidence and mortality were obtained from sentinel surveillance sites. The serological response to EZ measles vaccine was evaluated at a health centre in 1989 and in a community survey in 1990. RESULTS: Measles vaccine coverage estimated in cluster surveys increased from 50% of the 1984 birth cohort to 89% of the 1989 birth cohort, accepting either a home-based record or a verbal history of vaccination. Reported measles incidence per 10,000 [corrected] population decreased by over 90%, from 37.5 in 1980 (early vaccination years) to 1.6 in 1991. There was a relative decrease in the proportion of cases aged < 9 months (32% of cases in 1986-1987 and 23% of cases in 1990-1991) and an increase in the proportion aged > 23 months (29% of cases in 1986-1987 and 43% in 1990-1991). According to ELISA assays, 74-76% of children seroresponded to EZ vaccine administered at age 6-7 months under routine programme conditions. CONCLUSIONS: Measles can be controlled in urban areas, although it is difficult to determine how great a contribution vaccination at age 6 months makes over and above the achievement of high coverage.

Mild illness at or after measles vaccination does not reduce seroresponse in young children.

We analyzed data from a randomized trial of AIK-C, high-titre (EZ-H) or medium-titre EZ (EZ-M) vaccines in 3.5 and 6 month old infants in Kinshasa, Zaire, in which the occurrence of rhinorrhoea, cough, diarrhoea, fever, conjunctivitis or rash was monitored for 15 days post-vaccination (including the day of vaccination, day 0). We compared sero-response at 6 weeks and 6 months post-vaccination among children with and without mild illness at or after vaccination. Seroresponse tended to be higher in children with mild illness after vaccination than those without, whether days 0-7 or 8-15 were examined. For most symptoms, these differences did not reach statistical significance after adjusting for prevaccination maternal antibody level. However, in the EZ-M group, the proportion of children attaining at least the median post-vaccination antibody level was significantly higher in children with rhinorrhoea in days 0-7 post-vaccination than those without (adjusted odds ratio 2.6, 95% CI 1.08-6.27), as was that among children with at least one symptom in days 0-7 compared with children with no symptoms (adjusted OR 4.55, 95% CI 1.18-17.57). There were no significant differences in post-vaccination antibody levels among children with symptoms compared either to those without the specific symptom or those with no symptoms. Fever on the day of vaccination or at home visits on 7, 10 or 14 days post-vaccination, did not affect seroconversion or GMTs. Regression models showed no relation between the cumulative number of days with symptoms and antibody increase after vaccination. Analysis of antibody levels at 6 months post-vaccination showed no consistent differences according to presence or absence of symptoms. These findings provide further strong support to recommendations that mild illness is not a reason to delay measles vaccination.

Immunogenicity of high-titre AIK-C or Edmonston-Zagreb vaccines in 3.5-month-old infants, and of medium- or high-titre Edmonston-Zagreb vaccine in 6-month-old infants, in Kinshasa, Zaire.

The effect of measles vaccine potency was evaluated among 485 children aged 6 months, and the effect of vaccine strain was evaluated among 538 children aged 3.5 months, in Kinshasa, Zaire. Children aged 6 months were randomly assigned to receive either high-titre Edmonston-Zagreb (EZ-H), potency 5.7 log10/dose, or medium-titre EZ (EZ-M), potency 4.7 log10/dose, those aged 3.5 months were randomly assigned to receive either AIK-C, potency 5.5 log10/dose, or EZ-H, and were revaccinated with EZ-M vaccine at age 9.5 months. Measles antibodies were measured using the plaque reduction neutralization assay. Among children vaccinated at age 6 months, the seroresponse was significantly higher after EZ-H than EZ-M vaccine, with 92 and 83% seroconverting by 6 months postvaccination and 59 and 40% respectively having antibody titres > 200 mIU. Among children vaccinated at age 3.5 months, only 24% (AIK-C) and 22% (EZ-H) attained antibody titres > or = 200 mIU 6 months postvaccination. After revaccination at age 9.5 months, 81% of children in the AIK-C group and 73% in the EZ-H group had antibody levels > 200 mIU (p = 0.056). A retrospective survey was conducted in January 1993 to determine the mortality experience of vaccine groups, and information was obtained for 94% of the children. A total of 44 deaths (4%) were identified, with no significant differences between groups when stratified by age at vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)