Pandemics

A pandemic is the worldwide spread of a disease caused by a novel pathogen that can sustain human-to-human transmission across multiple regions and populations. The defining feature is global reach, rather than severity, though pandemics commonly impose substantial health burdens.

Pandemics are distinct from epidemics, which are outbreaks limited to a particular community or region, and from endemics, which persist at a relatively constant rate within a population. A pandemic typically involves a pathogen to which the population has little preexisting immunity and rapid, widespread transmission.

Causes and dynamics: Pandemics often begin with zoonotic spillover, when a pathogen crosses from animals to humans and acquires sustained human transmission. Global travel, urban density, and ecological changes can accelerate spread. The severity is influenced by virulence, population health, and the availability of countermeasures such as vaccines.

Impact and response: Pandemics place stress on health systems, disrupt economies, and affect daily life through measures such as testing, isolation, travel restrictions, and social distancing. Surveillance networks, rapid vaccine development, antiviral drugs, and coordinated international response are central to mitigation.

Notable examples: The Black Death in the 14th century, the 1918 influenza pandemic, the HIV/AIDS pandemic beginning in the late 20th century, and the COVID-19 pandemic that emerged in 2019 have shaped public health practices and policy.

Prevention and preparedness: Ongoing global surveillance, data sharing, and investment in vaccine technology, manufacturing capacity, and public health infrastructure are key. Equitable access to vaccines and treatments remains a core challenge in pandemic response.