Studies with dried and glycerinated smallpox vaccines of full and diminished potencies.

In a further vaccination and laboratory study with two dried smallpox vaccines (designated "P" and "Q") and one glycerinated vaccine, the potency of samples of each vaccine was deliberately lowered by exposure to heat. Groups of volunteers were vaccinated with the fully potent vaccines and with those of reduced potency. All subjects who developed a vesicular response were challenged one year later by revaccination with a potent vaccine, and the results obtained in the different groups were compared. No significant variation could be detected in the response of the different groups to the challenge vaccination. These findings indicate that if vesiculation is obtained with a vaccine, even though potency has been reduced to a point where it produces less than 50% successful primary vaccinations, satisfactory protection will result one year later. It also appears that successful vaccination with a dried vaccine confers as good immunity as that obtained from glycerinated lymph. Vaccines with a pock count of 10(6) infective units per millilitre will produce about 40% successes in primary vaccination.