A widespread endemic disease with a stable number of infected people is not a pandemic. Further, flu pandemics generally exclude recurrences of seasonal flu. Throughout history, there have been a number of pandemics of diseases such as smallpox and tuberculosis. One of the most devastating pandemics was the Black Death, which killed an estimated 75–200 million people in the 14th century. The current pandemics are HIV/AIDS and coronavirus disease 2019 (COVID-19) - the first pandemic that can be controlled. Other notable pandemics include the 1918 influenza pandemic (Spanish flu) and the 2009 flu pandemic (H1N1).
A pandemic is an epidemic occurring on a scale that crosses international boundaries, usually affecting a large number of people. Pandemics can also occur in important agricultural organisms (livestock, crop plants, fish, tree species) or in other organisms. A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For instance, cancer is responsible for many deaths but is not considered a pandemic because the disease is not infectious or contagious.
The World Health Organization (WHO) previously applied a six-stage classification that describes the process by which a novel influenza virus moves from the first few infections in humans through to a pandemic. This starts with the virus mostly infecting animals, with a few cases where animals infect people, then moves through the stage where the virus begins to spread directly between people, and ends with a pandemic when infections from the new virus have spread worldwide. In February 2020, the WHO clarified that "there is no official category for a pandemic".
The basic strategies in the control of an outbreak are containment and mitigation. Containment may be undertaken in the early stages of the outbreak, including contact tracing and isolating infected individuals to stop the disease from spreading to the rest of the population, other public health interventions on infection control, and therapeutic countermeasures such as vaccinations which may be effective if available. When it becomes apparent that it is no longer possible to contain the spread of the disease, management will then move on to the mitigation stage, in which measures are taken to slow the spread of the disease and mitigate its effects on society and the healthcare system. In reality, containment and mitigation measures may be undertaken simultaneously.
A key part of managing an infectious disease outbreak is trying to decrease the epidemic peak, known as "flattening the epidemic curve". This helps decrease the risk of health services being overwhelmed, and provides more time for a vaccine and treatment to be developed. Non-pharmaceutical interventions may be taken to manage the outbreak. In a flu pandemic, these actions may include: personal preventive measures such as hand hygiene, wearing face-masks, and self-quarantine; community measures aimed at social distancing such as closing schools and cancelling mass gatherings; community engagement to encourage acceptance and participation in such interventions; and environmental measures such as cleaning of surfaces.
- How can a particular disease be considered a pandemic?
- What makes a disease infectious?
- The WHO used a process to describe pandemic phases that is no longer used
- Containment and mitigation are basic strategies in the control of an outbreak that are undertaken in different stages
- Reducing peak burden on healthcare is a key part of managing an infectious disease outbreak