Potency and immunogenicity of bacillus calmette guerin (BCG) vaccines used in routine immunization programme in South-East, Nigeria

Abstract

The efficacy of every vaccine depends in part on appropriate vaccine handling from the manufacturer to its utilization. There is need for continuous monitoring of vaccine to ensure that cold-chain system is maintained throughout the product life-span. This study aims to validate the BCG vaccines used in immunization in South-East, Nigeria. The potency of the vaccines was determined by viable count on Soybean-Casein-Digest Agarafter incubation of 50µl of 1: 40,000 dilutions of the vaccines at 37°C for 30 days. Ten replicate plates were used and result reported as mean ±SD. The viable counts in the vaccines were compared with the labeled potency on the vials. The immunogenicity test was done by Antibody Induction Method. This involves measuring the neutralizing antibodies in a control group (given physiological saline) and immunized group after 30 days using the enzyme-linked immunosorbent assay (ELISA). Anti-tuberculosis antibodies’ concentration was determined by absorbance measurement at 450nm wavelength. Viable counts in the BCG vaccine samples were 54.6±11.79 > 51.91±11.35 > 48.18±15.33 > 44.91±16.29 > 44.55±15.69 CFU/50µl (dilution factor was 40,000). The immunogenicity test shows that the IgG titers for the BCG vaccines from control, Enugu/Ebonyi, Imo, Anambra and Abia were 0.645, 1.567, 1.507, 1.451 and 1.286 respectively while the IgMtitres were 0.689, 0.736, 0.805, 0.792 and 0.715 respectively. One way analysis of variance shows that there is statistical difference in the IgG antibody titer produced by the control compared to the vaccines (P value < 0.0001). The IgG antibody was enough to confer protection. Neither the control nor the vaccines from the states produced enough protective IgM. There is no statistical difference in the IgM antibody titer produced by the control compared to the vaccines (P value = 0.1058). The vaccines were all within their labeled potency and have good immunogenicity profile. Key words: Immunogenicity, potency, BCG vaccine, routine immunization programme, South-East, Nigeria.