EPI vaccines-induced antibody prevalence in 8–9 year-olds in The Gambia
We evaluated antibody prevalence to measles, polio 1 and 3, and tetanus toxoid antibodies in 8–9 year-old children in The Gambia within the framework of the Gambia Hepatitis Intervention Study (GHIS), a large vaccine trial aimed at evaluating vaccine efficacy against hepatitis B virus (HBV) infection, chronic carriage and primary liver cancer in a high risk population. The results of the present survey were compared with a previous survey performed with the same objectives and same methodology but in different children at 3–4 years of age. Methods
Four clusters of 200 children each were sampled as representative of the whole country. Children would have received BCG, diphtheria–pertussis–tetanus vaccine (DPT ), poliovirus vaccine (OPV), measles and yellow fever immunization. The measles haemoagglutination inhibition test (HAI) was used to detect measles antibody. Antibodies to polioviruses 1 and 3 were tested using the standard polio neutralization assay described in the EPI manual ( WHO 1990). An enzyme-linked immuno-sorbent assay (ELISA) was used to measure tetanus toxoid antibodies. Results
A high proportion of children were fully vaccinated in both age groups. Measles antibody concentrations were ≤1 : 8 in 8.2% of 8–9 year-old vaccinated children. In the previous survey of 3–4 year-old children this was 11.3%. In the present survey, GMC was lower than in the 3–4 year-old children; 88% of 3–4 year-olds and 89% of 8–9 year-olds had detectable antibody levels against poliovirus type 1. Fewer children at 8–9 years of age had antibodies against poliovirus type 3 than 3–4 year-olds (78%vs. 89%P < 0.001). A significant overall lower proportion of 8–9 year-old children had detectable tetanus toxoid antibodies compared to 3–4 year-old children (87%vs. 95%P < 0.001), as well as those who received four doses of DPT (90%vs. 97%P < 0.001). Conclusions
High vaccine coverage is achieved in The Gambia with EPI. With time the number of vaccinated children who are not protected against measles, poliovirus 3 and tetanus increases. Besides the maintenance of high vaccine coverage in infants and young children, booster doses of some of the EPI vaccines in adolescents should be considered.
Document Type: Research Article
Affiliations: 1: Gambia Hepatitis Intervention Study, International Agency for Research on Cancer (WHO), Lyon, France 2: London School of Hygiene and Tropical Medicine, London, UK 3: International Agency for Research on Cancer, Lyon, France 4: Medical Research Council, Fajara, The Gambia
Publication date: 2004-10-01