Thomas Francis Jr (1900-1969), American microbiologist. Whilst working at the New York University School of Medicine Francis isolated the influenza A (1934) and B (1940) viruses. He also developed, with Jonas Salk, a single vaccine against both viruses. However, he is best known for his work as the director of the Poliomyelitis Vaccine Evaluation Centre, where in 1954 he extensively tested Salk's polio vaccine. 650,000 children were either given the vaccine or a placebo. Their health was monitored along with 1.2 million control children. When the vaccine was proven to work Francis oversaw the mass vaccination of 7 million schoolchildren, virtually eradicating polio.