Study on the stability of 17D-204 yellow fever vaccine before and after stabilization.

To monitor the parameters controlling yellow fever vaccine production, eight different lots produced without stabilizers were studied. It was found that the freeze-thaw cycle did not have any adverse effect on virus infectivity and the mean loss in virus titre during lyophilization was 0.51 log10 ml-1. A thermodegradation study after storage of vaccine at different temperatures showed that the vaccine did not pass the accelerated stability test. To stabilize the 17D-204 substrain vaccine, four stabilizers with different sugars and amino acids were examined. The optimum time for addition of the stabilizers was found to be during homogenization of infected embryos. An accelerated stability test at 37 degrees C indicated that stabilizers S1, S2 and S3 kept the vaccine stable for up to 4 weeks, whereas the vaccine was only stable for up to 3 weeks in stabilizer S4. Stabilizer S3 was found statistically to be the best. Reproducibility in production methodology was established by preparing and testing more batches of the vaccine using stabilizer S3.