After returning, he received his undergraduate degree from Allegheny College in 1932.[1] Completing his medical training at Harvard Medical School in 1936,[1] Hammon then studied with the bacteriologist Hans Zinsser, receiving a Master of Public Health degree in 1938, and a Doctor of Philosophy degree in 1939.[3] During this period Hammon co-discovered the first vaccine for feline panleucopenia.[4]