Pandemic

A pandemic is the worldwide spread of a new disease across multiple countries or continents, affecting a large portion of the population. It differs from an epidemic, which is more limited to a region or community, and from a local outbreak. A pandemic is defined primarily by geographic spread rather than by the severity of illness.

Pandemics typically arise when a pathogen that is novel to humans gains efficient person-to-person transmission, often after crossing species barriers. Factors that can contribute include urbanization, global travel, population growth, animal reservoirs, and changes in the ecosystem. Immunity in the population is generally low for such new pathogens, allowing rapid spread.

Detection and response rely on global surveillance, reporting networks, and international health regulations. Organizations such as the World Health Organization monitor patterns of illness and may declare a pandemic when transmission levels reach across borders. Public health guidance may include testing, contact tracing, surveillance, and nonpharmaceutical measures, complemented by medical countermeasures when available.

Notable pandemics include the 1918 influenza pandemic, the HIV/AIDS pandemic that began in the late 20th century, the 2009 H1N1 influenza pandemic, and the COVID-19 pandemic declared in 2020. The impact of pandemics varies, with mortality, healthcare disruption, and economic consequences influenced by timing and public health capacity.

Preparedness and response focus on surveillance, rapid vaccine and therapeutic development, health system resilience, and equitable access to interventions. International cooperation and adherence to health regulations are central to coordinated action, along with transparent communication to maintain public trust during health emergencies.