Temperature stability of Beijing-1 master seed strain and working seed strain for production of inactivated Japanese encephalitis vaccine on Vero cell in Vietnam

Abstract

This study aims to assess the temperature stability of Beijing-1 master seed strain and working seed strain for production of
inactivated Japanese encephalitis vaccine on Vero cell in Vietnam, 2010 - 2020. The master seed lot (BV-MSV-0210) and working seed lot (BV-WSV-0310) were produced by Beijing-1 strain of Japanese encephalitis virus on vero cells line 1% gelatin added, and stored in liquid nitrogen from 2010 to 2020, has been evaluated the stability of virus titer according to time and temperature by flague forming unit (PFU) technique on vero cells. At the same time, the titre stability of the working seed lot was also studied at -20oC and 2-8oC. The results showed that the BV-MSV-0210 and BV-WSV-0310 storaged in liquid nitrogen, after 10 years there were still stability titers at 7,89 log PFU/ml and 7,53 log PFU/ml, respectively. The titer of BV-WSV-0310 stored at -20oC, after 1 month was 7,33 log PFU/ml (reduced 0.61 logPFU/ ml). After 3 months was 6.03 log PFU/ml. It was acceptable because of the limited titer ≥ 6 log PFU/ml. But after 6 months the titer was not acceptable at 5.28 log PFU/ml. Keeping at 2-8oC after 1 day, the virus titer was 6.77 log PFU/ml; after 3 days was 6,48 log PFU/ml. Following 5-7 days the titer reduced quickly, it was remained 5.55 log PFU/ml and 5.42 log PFU/ml, respectively. So the best way for keeping the stability of virus titer need to store the strains in liquid nitrogen -196oC.