Revaccination as a measure of immunity to smallpox

Abstract

1. Serological methods for the determination of smallpox immunity are briefly discussed, and it is concluded that they are unlikely to provide a diagnostic method of sufficient accuracy.2. Experimental work is recorded which shows certain differences in the response of previously vaccinated individuals, revaccinated simultaneously with a standard vaccine lymph and an elementary body suspension (vaccinia) of high potency. The significance of these differences is discussed.3. The results indicate that although the advantage of the e.b. suspension over vaccine lymph is relatively insignificant, that of two insertions over one is very marked. In revaccination the routine use of one insertion only may result in a certain number of semi-immunes (vaccinoids) being erroneously reported as immunes.4. It is concluded that if the two insertion technique be practised, persons showing immune reactions (negatives) may be considered, in all probability, as possessing full immunity to vaccinia-variola virus.