Studies on Measles Virus

In the presence of serum, measles virus was kept in the refrigerator for 6 to 8 months or at −72°C for over a year with little drop in titer. Thermal inactivation studies indicated that the virus was relatively unstable at 25°C and at 37°C, with a rapid initial rate of inactivation followed by a “tailing effect” of longer duration. At 25°C, the virus was most stable at pH values between 7 and 8. The virus could be lyophilized without significant loss of titer. Ultracentrifugation studies indicated a particle size for the infective unit of approximately 140 mμ. Difficulty was encountered in passing the virus through bacteria-retaining filters; best recovery was obtained with the clarifying stainless sintered steel filters and with the sterilizing Millipore filters. It was found that measles virus was readily inactivated by either γ- or β-radiation.