- Emergence of New Pathogens: Novel infectious agents can emerge and spread rapidly before effective countermeasures are developed. - Antimicrobial Resistance: The rise of _antimicrobial resistance_ makes it increasingly difficult to treat infections. - Vaccine Hesitancy: Reluctance or refusal to vaccinate can undermine public health efforts to control diseases. - Globalization: Increased travel and trade can facilitate the rapid spread of diseases across borders.