[1][2] Their research led to the identification of three distinct serotypes of poliovirus, all of which must be incorporated for a vaccine to provide complete immunity from poliomyelitis.

Between 1944 and 1949, their work led to the identification of three distinct serotypes of poliovirus, all of which must be incorporated for a vaccine to provide complete immunity from poliomyelitis.

[1][10] She also began experiments to immunize monkeys against polio with killed poliovirus grown in nervous tissue and inactivated with formaldehyde.

In these experiments, Morgan defined the number of antibodies that needed to circulate in the blood to protect monkeys from an intra-cerebral challenge from the poliovirus.

[12] Maurice Brodie had demonstrated a similar effect of immunity with inactivated virus in 1935, but others had been unable to reproduce his reports, and the approach had been discredited.

[10][2] In 1949, Morgan left Johns Hopkins and married former Air Force Colonel Joseph Mountain, who was a data processor in New York.

[1][10] She did however publish further articles relating to polio, in which she is credited as Isabel Morgan Mountain, PhD., while working with Hattie Alexander, a pediatrician interested in bacterial infections.

After her stepson Jimmy Mountain was killed in an air crash in 1960, she decided to leave Alexander's lab and eventually earned a master's degree in biostatistics from Columbia University.

After leaving polio research, she worked with a variety of individuals, including her husband, on the epidemiological studies of the effects of air pollution.