Fig. 2.

Timeline of vaccines and adjuvants development. Shown is an historical view of the origin and development for some early and currently licensed human vaccines, the time needed to translate a scientific discovery (shown in red) into a safe and scalable vaccine technology (orange bars), the evolution of adjuvants, and of some supporting areas of science and technology. The blue bars represent the time needed to develop and implement one or more vaccines derived from the same technology. IPV, inactivated polio virus; OPV, oral polio virus; Hib, Haemophilus influenzae type b; HBV, hepatitis B virus; HPV, human papillomavirus. Reproduced from Rappuoli et al. (2014), with permission of the author and publisher, Proceedings of the National Academy of Sciences [2].