Pandemic
A pandemic is an epidemic of an infectious disease that has a sudden increase in cases and spreads across a large region, for instance multiple continents or worldwide, affecting a substantial portion of the human population. Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide.
Throughout human history, there have been a number of pandemics of diseases such as smallpox. The Black Death, caused by the Plague, caused the deaths of up to half of the population of Europe in the 14th century. The term pandemic had not been used then, but was used for later epidemics, including the 1918 H1N1 influenza A pandemic—more commonly known as the Spanish flu—which is the deadliest pandemic in history. The most recent pandemics include the HIV/AIDS pandemic, the 2009 swine flu pandemic and the COVID-19 pandemic. Almost all these diseases still circulate among humans though their impact now is often far less.
In response to the COVID-19 pandemic, 194 member states of the World Health Organization began negotiations on an International Treaty on Pandemic Prevention, Preparedness and Response, with a requirement to submit a draft of this treaty to the 77th World Health Assembly during its 2024 convention. Further, on 6 May 2024, the White House released an official policy to more safely manage medical research projects involving potentially hazardous pathogens, including viruses and bacteria, that may pose a risk of a pandemic.
Definition
The word comes from the Greek παν- pan- meaning, and δῆμος demos, hence "common to all the people" cf. Aphrodite Pandemos. The term survives until today in Modern Greek with the meaning "all-people's" or "concerning all the people" i.e. "a pandemic assembly".A medical dictionary definition of pandemic is "an epidemic occurring on a scale that crosses international boundaries, usually affecting people on a worldwide scale". 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 contagious—i.e. easily transmissible—and not even simply infectious. This definition differs from colloquial usage in that it encompasses outbreaks of relatively mild diseases.
The World Health Organization has a category of Public Health Emergency of International Concern, defined as "an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response". There is a rigorous process underlying this categorization and a clearly defined trajectory of responses.
A WHO-sponsored international body, tasked with preparing an international agreement on pandemic prevention, preparedness and response has defined a pandemic as "the global spread of a pathogen or variant that infects human populations with limited or no immunity through sustained and high transmissibility from person to person, overwhelming health systems with severe morbidity and high mortality, and causing social and economic disruptions, all of which require effective national and global collaboration and coordination for its control".
Parameters
A common early characteristic of a pandemic is a rapid, sometimes exponential, growth in the number of infections, coupled with a widening geographical spread.WHO utilises different criteria to declare a Public Health Emergency of International Concern, its nearest equivalent to the term pandemic. The potential consequences of an incident are considered, rather than its current status. For example, polio was declared a PHEIC in 2014 even though only 482 cases were reported globally in the previous year; this was justified by concerns that polio might break out of its endemic areas and again become a significant health threat globally. The PHEIC status of polio is reviewed regularly and is ongoing, despite the small number of cases annually.
The end of a pandemic is more difficult to delineate. Generally, past epidemics and pandemics have faded out as the diseases become accepted into people's daily lives and routines, becoming endemic. The transition from pandemic to endemic may be defined based on:
- a high proportion of the global population having immunity
- fewer deaths
- health systems step down from emergency status
- perceived personal risk is lessened
- restrictive measures such as travel restrictions removed
- less coverage in public media.
Prevention and preparedness
Pandemic prevention comprises activities such as anticipatory research and development of therapies and vaccines, as well as monitoring for pathogens and disease outbreaks which may have pandemic potential. Routine vaccination programs are a type of prevention strategy, holding back diseases such as influenza and polio which have caused pandemics in the past, and could do so again if not controlled. Prevention overlaps with preparedness which aims to curtail an outbreak and prevent it getting out of control - it involves strategic planning, data collection and modelling to measure the spread, stockpiling of therapies, vaccines, and medical equipment, as well as public health awareness campaigning. By definition, a pandemic involves many countries so international cooperation, data sharing, and collaboration are essential; as is universal access to tests and therapies.Collaboration – In response to the COVID-19 pandemic, WHO established a Pandemic Hub in September 2021 in Berlin, aiming to address weaknesses around the world in how countries detect, monitor and manage public health threats. The Hub's initiatives include using artificial intelligence to analyse more than 35,000 data feeds for indications of emerging health threats, as well as improving facilities and coordination between academic institutions and WHO member countries.
Detection – In May 2023, WHO launched the International Pathogen Surveillance Network aiming to detect and respond to disease threats before they become epidemics and pandemics, and to optimize routine disease surveillance. The network provides a platform to connect countries, improving systems for collecting and analysing samples of potentially harmful pathogens. Wastewater surveillance can for example provide early warnings by detecting pathogens in sewage.
Therapies and vaccines – The Coalition for Epidemic Preparedness Innovations is developing a program as part of their 2022–2026 pandemic plan to condense new vaccine development timelines to 100 days, less than a third of the time it took to develop a COVID-19 vaccine. In the US, the National Institute of Allergy and Infectious Diseases has developed a Pandemic Preparedness Plan which focuses on identifying viruses of concern and developing diagnostics and therapies to combat them.
Modeling is important to inform policy decisions. It helps to predict the burden of disease on healthcare facilities, the effectiveness of control measures, projected geographical spread, and timing and extent of future pandemic waves.
Public awareness involves disseminating reliable information, ensuring consistency in message, transparency, and steps to discredit misinformation.
Air quality – Enhanced indoor ventilation and air filtration systems are also effective at reducing transmission of airborne pathogens, while providing additional health benefits beyond pandemic control.
Stockpiling involves maintaining strategic stockpiles of emergency supplies such as personal protective equipment, drugs and vaccines, and equipment such as respirators. Many of these items have limited shelf life, so they require stock rotation even though they may be rarely used.
Ethical and political issues
The COVID-19 pandemic highlighted a number of ethical and political issues which must be considered during a pandemic. These included decisions about who should be prioritised for treatment while resources are scarce; whether or not to make vaccination compulsory; the timing and extent of constraints on individual liberty, how to sanction individuals who do not comply with emergency regulations, and the extent of international collaboration and resource sharing.Pandemic management strategies
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 curve". This helps decrease the risk of health services being overwhelmed and provides more time for a vaccine and treatment to be developed. A broad group of 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 canceling mass gatherings; community engagement to encourage acceptance and participation in such interventions; and environmental measures such as cleaning of surfaces.
Another strategy, suppression, requires more extreme long-term non-pharmaceutical interventions to reverse the pandemic by reducing the basic reproduction number to less than1. The suppression strategy, which includes stringent population-wide social distancing, home isolation of cases, and household quarantine, was undertaken by China during the COVID-19 pandemic where entire cities were placed under lockdown; such a strategy may carry with it considerable social and economic costs.