Universal vaccines: shifting to one for many or shooting too high too soon!

Switching from conventional strain-specific vaccines to multi-strain or multi-species universal vaccines is both justified and scientifically merited. Long-term cross-protective universal vaccines eliminate the need for repetitive short-term vaccination campaigns and short-notice vaccine redesign during impending epidemics. They also have the potential to be cost-effective, convenient, and amenable to stockpiling. Ongoing advances in genomics and reverse vaccinology along with the perceived ability of vaccines, if properly formulated, to induce cross-protective adaptive immunity and long-term T cell memory are at the heart of this trend. Consequently, the search for universal vaccines against influenza, HIV, and many other viral, bacterial, and fungal pathogens has intensified in recent years. Currently, several universal influenza vaccines are at different phases of clinical evaluation. That said, vaccine-related differential effectiveness, escape mutants, pathogen strain replacement, limited scope of cross-protective immunity, and diminished potential to reach optimal herd immunity thresholds present serious challenges to the concept and applicability of universal vaccines. Herein, the case for and the case against universal vaccines are investigated to realistically appreciate their prospects of success.