Understanding the host-pathogen interaction saves lives: lessons from vaccines and vaccinations.

Vaccines are one of the most successful and cost-effective public health tools employed to date, yet these benefits are only realized when the life-saving intervention reaches each and every targeted individual. Vaccine development is prioritized based on a number of factors such as health burden, feasibility, and determination of potential target populations. But only through an arduous process of pre-clinical development and progressive clinical trials does a vaccine become licensed and recommended for use. Once used in a wider and more diverse population safety issues, long-term impact and other unintended outcomes may become apparent, influencing policy modification. This commentary explores the role host-pathogen interaction plays in vaccine development and the operational and policy considerations that may impact vaccine success post-licensure.