She and Sarah Elizabeth Stewart are known for their discoveries related to cancer-causing viruses, particularly polyomavirus, such as SV40, a cancer-causing monkey virus that millions of people were exposed to through contaminated polio vaccines. Building on earlier work by Ludwig Gross, Sarah Elizabeth Stewart and Bernice East. Eddy were the first to describe the polyoma virus. Working together, they satisfied Koch"s postulates to demonstrate polyomavirus can cause cancer to be transmitted from animal to animal.
The virus was later named the Southeast polyoma virus in their honor.
In 1954, while the National Institutes of Health was testing the first commercial polio vaccines, Eddy"s job was to test the vaccines from five different companies. Testing the vaccines on 18 monkeys, she and her team discovered that the inactivated vaccine manufactured by Cutter Laboratories contained residual live poliovirus, resulting in the monkeys showing polio-like symptoms and paralysis.
Eddy reported her findings to William Workman, head of the Laboratory of Biologics Control, but her findings were never given to the vaccine licensing advisory committee. Although then-National Institutes of Health director William Sebrell was notified, he chose to ignore Eddy"s findings and proceeded to license the Cutter vaccine along with the others
In 1961, Eddy showed that an extract of monkey kidney cells used to propagate polio vaccine would cause tumors in newborn hamsters.
She followed up in 1962 to identify the SV40 as the virus present in these cells and in the Salk polio vaccine that caused the tumors. Previously, in 1960, Ben Sweet and Maurice Hilleman published similar results, leading Merck to voluntarily withdraw its killed-virus polio vaccine. In 1998, the National Cancer Institute undertook a large study, using cancer case information from the Institute"s SEER database.
The published findings from the study revealed that there was no increased incidence of cancer in persons who may have received vaccine containing SV40.
Another large study in Sweden examined cancer rates of 700,000 individuals who had received potentially contaminated polio vaccine as late as 1957. The study again revealed no increased cancer incidence between persons who received polio vaccines containing SV40 and those who did not.
The question of whether SV40 causes cancer in humans remains controversial however, and the development of improved assays for detection of SV40 in human tissues will be needed to resolve the controversy.