Biological feasibility of developing prophylactic vaccines for viral pathogens: incubation period as a critical parameter.
Vaccines for sixteen major human viral pathogens have been approved for use in humans. For most other major human viral pathogens, the absence of an efficacious prophylactic vaccine is not for lack of effort. To identify the key parameters of biologic feasibility that determine "certainty-of-success" for developing prophylactic vaccines for major human viral pathogens, basic characteristics of viruses, such as primary genomic structure, route of transmission, and durability of viral infection were reviewed. These basic characteristics of viruses simply do not associate with successful vaccine development, so one must look elsewhere for characteristics predictive of successful vaccine development. Herein existing data are put forth in a way that demonstrates the impact of the combined effect of incubation period and broadly protective, relative immunogenicity on the "certainty-of-success" of developing effective vaccines for thirty viral pathogens. Both incubation period and broadly protective, relative immunogenicity appear to have accounted for much of the past successes in vaccine development, and may be useful in predicting where near term successes are most apt to occur.