Pathogenicity and immunogenicity in mice of vaccinia viruses mutated in the viral envelope proteins A33R and B5R

The pathogenicity and immunogenicity in mice of WR.cl and WR.c3, two mutants of the Western Reserve (WR) strain of vaccinia virus, mutated in the A33R and B5R proteins of the outer envelope of the virus, respectively, were studied. WR.c1 was the most attenuated virus, WR.c3 was somewhat more pathogenic, while WR was the most virulent of the three. While the WR and the WR.c3 viruses, intranasally inoculated into mice, spread efficiently to the different internal organs of the animal, including the brain, WR.c1 was restricted to the lungs only. Mice, intranasally infected with 500 plaque forming units of the WR, WR.c1, or WR.c3 viruses, were protected against infection with a lethal dose of the WR strain.