By the time that Salk and Sabin began their race to find a vaccine, some of the most basic questions about the virus had been answered. Karl Landsteiner in 1908 took a liquid sample from the spinal cord of a boy who had just died of polio and passed it through a filter. Landsteiner then injected the sample into the stomachs of two rhesus monkeys, one of whom quickly became paralyzed. Since a bacterium is bigger than a virus and would have been unable to pass through the filter, the experiment established that polio was caused by a virus.
A virus always needs a host—a living entity for its own survival—but in the case of the poliovirus, the carrier might be asymptomatic.
The next big question to solve was the portal of entry. How did the virus get into the body? For a while, it was thought the virus entered through the nasal passages. All sorts of chemicals were inserted into nostrils to develop a barrier. Even Sabin came up with his own nasal barrier, but then he took on performing autopsies of those who had died from the poliovirus. When he found no virus in the nasal passages but found virus in the alimentary tract on its way to the stomach, he established that the virus was spread by the fecal-oral route, entering through the mouth and multiplying in the intestine and then passed from child to child.
Thus began Sabin and Salk’s great disagreement. Sabin set about producing a vaccine with a small amount of live attenuated virus on a sugar cube for a child to swallow, so as to travel the usual way though the body to produce lifelong immunity. Salk believed that a dead poliovirus should be injected into the body to call up antibodies to fight off an invasion by a live virus. His method was to trick the body into reacting as if it had already had the virus.
In either man’s theory, a large quantity of poliovirus would be needed, and it was believed that the poliovirus could only exist in nerve tissue. Then, in 1947, in a lab at Boston Children’s Hospital, John Enders—a charming, happy-go-lucky physician-scientist who later came up with the measles vaccine—told residents Tom Weller and Fred Robbins to see if the poliovirus would grow in kidney and other tissues. They had been working on the chickenpox virus but that day had several strains of poliovirus stored in the lab.