Efficiency of Freeze-Drying and Stability in Stress Conditions of Measles Vaccine Reference Standard - ประสิทธิภาพของการทำแห้งและ ความคงตัวที่สภาวะเร่งของวัคซีนหัดอ้างอิงมาตรฐาน

Vaccine reference standards are used by a national control laboratory for quality control of vaccine products. The purpose is to use vaccine reference standard calibrated against an international reference standard for being control of testing results in laboratory. Therefore, testing vaccine samples should always be tested in parallel with a vaccine reference standard. In this study, a measles virus vaccine was prepared in the laboratory by virus cultivation on monolayer of Vero cells and a known viral titer was formulated with a suitable formula of the freeze-drying process in order to store it for a long time. After freezedrying, the efficiency of freeze-dried vaccine was performed on determination of physical characteristics, moisture content, and potency as well as other related parameters before evaluating the stability of the vaccine in stress conditions. The test results showed that the lyophilized measles vaccine had good physical characteristics, a low residual moisture content of 1.50% and a high potency value of 5.29 logCCID50/ 0.5 milliliter. Tests on other parameters revealed that the variation of filling was 0.35%, reconstitution time was approximately 1.38 minutes and pH value was 7.32; and the vaccine was free from bacterial, fungal and mycoplasma contamination. The stability test of the vaccine in stress conditions at higher temperatures (4, 20, 37 and 45°C) after various time periods (1, 2, 3, 4, 6, 8 and 12 weeks) by storage the vaccine at -70°C and -20°C showed that the vaccine potency values were not different. Therefore, the vaccine can be stored at either -70°C or -20°C. However, the vaccine kept at -70°C or -20°C was found to lose potency at higher temperatures and longer storage time. Conversely, the vaccine showed good stability at -70°C, -20°C and 4°C for 12 weeks, indicating by the loss of the vaccine potency was not more than 1 logCCID50 of the normal potency value at 5.29 logCCID50/0.5 milliliter. The study confirmed that the measles virus vaccine prepared in the laboratory can be used as a vaccine reference standard for the control of potency values of measles vaccine, whereas in real storage conditions, the vaccine potency values should be continuously monitored to evaluate the long-term stability of the vaccine. Key words: measles virus vaccine, vaccine reference standard, potency, stability