Inactivation of Viruses for Vaccines **

Several attempts have been made to use ionizing radiation as a means of inactivating viruses so that they can be employed as killed vaccines. Success has been achieved with a rabies virus, and trials have also been made with poliomyelitis virus.""7 These methods have not been used for practical purposes, partly because of their novelty, because of the expense in the original setting up of the equipment, and partly because successful vaccines have been produced by other means. In the light of modern studies of radiation action on viruses, it seems worth while to consider the relative advantages of ionizing radiation for inactivating viruses. We wish to see whether the expense and elaboration necessary might be practical. To do this we need to evaluate the fundamental studies of the action of ionizing radiation on viruses. This work has been in progress since 1937 and was begun separately in three nations by Holweck and co-workers in Paris, Lea and co-workers in England, and Gowen and Price in the United States.'5 The use of ionizing radiation to measure virus size, in particular, has been exploited by Bonet-Maury.5 A large share of the work in the Biophysics Department at Yale University for the past six years has been on the inactivation of viruses by ionizing radiation. This study has been concerned with the effects of radiation in many properties of bacterial, plant, and animal viruses. To summarize the results we can say that the infectivity property of viruses is highly sensitive to ionizing radiation. It can be characterized in terms of relative volume by saying that the sensitive volume for inactivation of a virus by ionizing radiation is rarely less than 1/20 of the whole virus. In terms of densely ionizing particles such as deuterons or alpha particles the sensitive area which is then concerned with such inactivation is very rarely less than one-half of the area of the whole virus. In strong contrast to the infectivity is the sensitivity of serological combination. For tobacco mosaic virus sensitivity is very low, so that measurements have hardly been possible because of the side-effects produced by the * Professor of Biophysics.