Well before the United States entered World War II, leaders of federal and private health agencies began assessing the situation in Europe and Africa. Early in the summer of 1940, the Rockefeller Foundation board of directors voted to budget $500,000 for public health work in Europe related to war conditions. Sawyer spent August and September traveling in Spain, France, and Portugal, and England, meeting with IHD staff, local health officials and researchers, and representatives from the American Red Cross and American Friends Service Committee. In December he returned as part of the U.S. Health Commission to Europe. With U.S. Surgeon General Thomas Parran and Children's Bureau Chief Martha Eliot, he continued to assess and plan for relief and disease-control efforts. These included everything from food supplies and nutritional supplements to vaccines for influenza, typhus, and yellow fever. In addition to his Rockefeller Foundation duties, Sawyer served on the Subcommittee on Tropical Diseases of the National Research Council, as director of the Commission on Tropical Diseases under the Board for the Investigation of Epidemic Diseases in the Army, and as consultant to the Medical Department of the Navy.
Meanwhile, Colonel James Simmons of the Army Surgeon General's Office, anticipating American involvement in the war, asked the RF to increase its production of 17D yellow fever vaccine, so that all military personnel going into tropical areas could be protected. Sawyer agreed, but recommended that the Public Health Service set up its own vaccine production plant as soon as possible. By early 1941, the RF was producing 50,000 doses of vaccine per week. The Public Health Service was negotiating with pharmaceutical companies to take over manufacture, but the price quoted was high, and the RF labs would have to train personnel and do quality control during the initial period. RF president Raymond Fosdick (advised by Dr. Andrew Warren, acting head of IHD while Sawyer was in Europe) told the Surgeon General that the RF could meet the entire need of the armed forces, and would do so gratis, as its contribution to the war effort.
The agreement was made by the time Sawyer returned from Europe in March of 1941, so he made arrangements for the increased vaccine production. Several methods of vaccine manufacture were available by then; the RF standard used human blood serum obtained from a standard pool of blood donors in New York. Because the immunization campaign in Brazil had encountered problems with jaundice occurring seven weeks to eight months after vaccination, a non-serum preparation method had been developed. The serum-free vaccine did not seem to produce jaundice, but it was still far from clear what had caused it earlier. Several experts theorized that another virus had been carried in the serum. Heating the serum to temperatures known to kill viruses seemed to resolve the problem. Because the serum-free vaccine had not been widely field-tested, and there was no time to do such testing, Sawyer and Bauer decided to stay with the serum-based vaccine.
After the U.S. entered the war in late 1941, the army started vaccinating all troops, not just those headed to tropical areas. By early April 1942, the IHD had furnished seven million doses to the U.S. Army and Navy, British forces in Africa, and others. In March, however, many cases of hepatitis--mostly mild--were being reported in American troops especially in California. Sawyer and Bauer went out to investigate, and within a month the evidence pointed to infection from nine specific lots of vaccine. These, in turn were traced to 2 percent of the blood donors, who had histories of hepatitis but no symptoms at the time they gave the blood. The level of production had required a much larger pool of blood donors for the serum, and no one had checked on their medical histories.
At Sawyer's direction, the IHD converted to serum-free vaccine production by June of 1942, but in the end there were still over 49,000 cases of vaccine-related hepatitis that year, 84 of them fatal. Sawyer was harshly criticized for his error in judgment, and for making what appeared to be a unilateral decision. Characteristically, he shouldered all of the blame, without pointing to others who might have shared it.
Several positive outcomes of this episode were largely overlooked at the time: first, it substantially advanced scientific understanding of viral hepatitis, and made clear the differences between infectious and serum hepatitis (now called hepatitis A and hepatitis B, respectively). Second, during the remainder of the war, there were no cases of yellow fever reported among American troops.
Besides its yellow fever vaccine, the IHD made other notable contributions to the war effort. It was clear that when the Allied forces succeeded in moving into Italy (which they did in October of 1943), conditions in the war-torn areas could easily foster epidemics of diseases such as typhus fever and malaria. Sawyer and IHD associate director George Strode created the RF Health Commission to help formulate disease control strategies in the Mediterranean. IHD officers such as Fred Soper and J. Austin Kerr played key roles in these efforts, and succeeded in limiting the spread of typhus in Naples, and eliminating malaria in the Nile valley, in Rome, and later in Sardinia.