 Oswald Avery, Colin MacLeod, and Maclyn McCarty later showed that the transforming factor was deoxyribonucleic acid, or DNA.Serum therapy for infectious diseases was displaced by antibiotics in the 1940s, but identification of specific serotypes remained important as the understanding of the epidemiology of pneumococcal infections still required their identification to determine where different serotypes spread, as well as the variable invasiveness of different serotypes.Understanding the prevalence of various serotypes was also critical to the development of pneumococcal vaccines to prevent invasive infections.