The use of smallpox vaccine.

The author first discusses the developments made in the last thirty years in methods of destroying contaminating micro-organisms and of reducing the amount of extraneous tissue debris, in cultivating virus in the embryonated egg and in tissue culture, in producing stable dried vaccine, and in methods of titrating the potency of vaccine. As to the strain of virus to be used in vaccines, he does not consider it necessary to use strains which have periodically been passed through the human subject.He then discusses a trial of the stability of dried smallpox vaccine which is being conducted by the World Health Organization and the characteristics of a dried vaccine developed at the Lister Institute of Preventine Medicine. Encouraging results have also been achieved there in the production and use of virus inactivated by ultraviolet irradiation, in order to decrease the risk of complications consequent upon the use of living virus vaccine.Consideration of the duration of immunity and the protection afforded after contact with smallpox leads to the conclusion that complete protection may be expected in most cases if vaccination is carried out within 24 hours of exposure, but that if vaccination is delayed more than three days it will have little influence on the infection.