Trend analysis of potency and stability of measles vaccine in India

Purpose: Efficacy of live viral vaccines is dependent on proper attenuation of vaccine virus. In addition to attenuation, cold chain maintenance also becomes essential to ensure vaccine quality till it reaches the end user. The transport of vaccines with required cold chain in tropical countries like India is comparatively difficult due to its hot and humid environment. The present study was carried out to see the trend analysis of 95 batches of measles vaccine stored at 2-8°C and their thermo stability after exposure at 37°C for 7 days, as such no study is published from India. Methods: All the vaccines included in the study were tested in triplicates against reference vaccine as per the WHO method. The number of wells positive for syncytia formation was counted and titres were calculated using Spearman-Karber Method. The geometric mean titre was calculated for the triplicate readings. The assay is considered valid only if confidence limits (P=0.95) of the logarithm of the virus concentration is greater than ±0.3. WHO criteria state that minimum virus concentration should be 103.0 CCID50 per human dose for both exposed and non-exposed measles vaccine. Also, after incubation the loss in titre should not be more than 101.0. Results: The potency and thermo stability titres of all the batches tested were found to be 103.45 to 104.5 and 103.11 to 103.65 respectively and were within prescribed specifications of WHO. Conclusions: Potency and thermo stability of the measles vaccine tested were found in the acceptable range indicating measles vaccine is quite potent, thermostable and suitable for country like India.