Because the benefits of rabies vaccines typically take a few days to kick in, antibodies such as these would be used initially in cases of severe animal bites. “A vaccine might be too late to develop [natural] antibodies,” Koprowski says. “The recommendation is to first inject the antibody serum, then give the vaccine,” which in turn elicits the production of antibodies for long-term protection. The need for commercially available antibodies for such animal-bite treatments against rabies is great; up to 50,000 cases of human rabies occur annually in Asia alone, 40 percent in children.

Dr. Koprowski has also been a lightning rod for controversy over his work in 1950s Africa dispensing polio vaccines some think were contaminated with simian viruses during the manufacturing process, accidentally caused the ongoing AIDS epidemic. The charge remains unproven and is fiercely protested by Koprowski. Nonetheless, he noted to Reuters that “it is safer to use plants to make antibodies than animals…for animals are more likely to carry something that can be dangerous to humans.” He said he and his colleagues chose to work with tobacco plants because they can be grown in different regions around the world.