The World Health Organization included vaccine hesitancy on the list of threats to global health in 2019. Vaccine hesitancy is a complex matter, with rationale ranging from accessibility to personal belief. Whatever the reason, the global effect of not vaccinating has created significant issues. Vaccination currently prevents about 2-3 million deaths per year. Some countries that were close to eradicating certain diseases (e.g., measles) have noticed an increase in cases. Read more about the top threats to global health.