ABSTRACT
@#Objective To develop and verify a plaque method for detection of infectious titer of tick-borne encephalitis virus(TBEV)strain(PHKT strain for short)adapted to primary hamster kidney(PHK)cells.Methods PHK cells were infected with TBEV,a primary mouse brain adaption strain,and passed consecutively for 12 passages.The titer of PHKT was detected by plaque method(Monolayer BHK-21 cells were infected with PHKT of various passages at different dilution ratios,and the plaque number was calculated by neutral red staining)and challenge titration in mouse brain(Mice were challenged with PHKT of various passages at different dilution ratios through brain cavity,0.03 mL for each,observed continuously for 14 days,and calculated for the median lethal dose(LD50)by Reed-Muench method)respectively,and the correlation between the results of two methods was analyzed.The developed plaque method for the detection of TBEV titer was verified for specificity,repeatability and intermediate precision.Results The plaque titer of PHKT virus was up to8.9 lgPFU/mL;The correlation between the results of plaque method and mouse brain challenge titration method was good(r = 0.92);The specificity of plaque method for detecting infectious titer of PHKT virus was good,and the coefficients of variation(CVs)of repeatability and intermediate precision were both less than 5%.Conclusion A plaque method for detecting infectious titer of PHKT virus was developed,which may be used as an alternative method for challenge titration in mouse brain.
ABSTRACT
Background: Measles vaccine was the only vaccine in the expanded vaccination program still must be imported. Center for research and production of vaccines and biologicals \ufffd?Ha Noi was conducting the first stages of measles vaccine manufacturing technology transfer from the Kitasato Institute in Japan. The Center received semi-finished vaccine to set up finished vaccine production process as well as the testing process. Potency test and its consistency is very essential in quality control. Objectives: In order to identify standard potency assessment methods and potency of 13 lots of finished measles vaccine produced in Viet Nam from imported semi-finished products. Subjects and method: 13 lots of the finished vaccine were determined potency by plaque method based on 13 samples of semi-finished vaccine and the standard sample M16-6 had potency from 4.2 to 4.6 lg PFU/0.5 ml provided by the Kitasato Institute. Results: The result of 13 lots show that the reduction of potency during freeze-drying is within the range (0-0.76 lg); and 4 last consecutive lots are met WHO criteria on heat stability. Conclusion: This shows that the measles vaccine freeze-drying process in Vietnam was officially set up to use for the measles vaccine production in 2007.