Endemic COVID-19

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COVID-19 is predicted to become an endemic disease by many experts. The observed behavior of SARS-CoV-2, the virus that causes COVID-19, suggests it is unlikely it will die out, and the lack of a COVID-19 vaccine that provides long-lasting immunity against infection means it cannot immediately be eradicated; [1] thus, a future transition to an endemic phase appears probable. In an endemic phase, people would continue to become infected and ill, but in relatively stable numbers. [1] Such a transition may take years or decades. [2] Precisely what would constitute an endemic phase is contested. [3]

Contents

Endemic is a frequently misunderstood and misused word outside the realm of epidemiology. Endemic does not mean mild, or that COVID-19 must become a less hazardous disease. The severity of endemic disease would be dependent on various factors, including the evolution of the virus, population immunity, and vaccine development and rollout. [2] [4] [5]

COVID-19 endemicity is distinct from the COVID-19 public health emergency of international concern, which was ended by the World Health Organization on 5 May 2023. [6] Some politicians and commentators have conflated what they termed endemic COVID-19 with the lifting of public health restrictions or a comforting return to pre-pandemic normality.

Definition and characteristics

In an endemic phase, the number of infections can be high or low, as long as it stays within the predicted range. Superposition of two simple harmonic motions, almost equal frequencies.png
In an endemic phase, the number of infections can be high or low, as long as it stays within the predicted range.

An infectious disease is said to be endemic when the number of infections is predictable. [7] This includes diseases with infection rates that are predictably high (called hyperendemic ), as well as diseases with infection rates that are predictably low (called hypoendemic). [7] Endemic does not mean mild: a disease with a stable infection rate can be associated with any level of disease severity and any mortality rate among infected people. [8] Endemic COVID-19 is not a synonym for COVID-19 infection becoming safe, or for mortality and morbidity becoming less of a problem. The prevalence and resulting disease burden is dependent on factors such as how quickly new variants emerge, the uptake of COVID-19 vaccines, and changes to disease virulence (a factor that depends on both the virus's own characteristics and people's immunity against it), rather than being dependent on endemicity. [2]

Generally speaking, all new emerging infectious diseases have five potential outcomes: [5]

Additionally, if an infectious disease becomes endemic, there is no guarantee that the disease will remain endemic forever. A disease that is usually endemic can become epidemic or pandemic in the future. [5] For example, in some years, influenza becomes a pandemic, even though it is not usually a pandemic.

During the course of the COVID-19 pandemic, it became apparent that the SARS-CoV-2 virus was unlikely to die out. [1] Eradication is widely believed to be impossible, especially in the absence of a vaccine that provides long-lasting immunity against infection from COVID-19. [1]

While all of the other outcomes are possible – sporadic, epidemic, pandemic, or endemic – many experts believe that COVID-19 is most likely to become endemic. [1] [5] Endemicity is characterized by continued infections by the virus, but with a more stable, predictable number of infected people than in the other three categories.

There is no single agreed definition or metric that proves that COVID-19 has become endemic. [10]

Endemic epidemiology

A March 2022 review said that it was "inevitable" the SARS-CoV-2 virus would become endemic to humans, and that it was essential to develop public health strategies to anticipate this. [4] A June 2022 review predicted that the virus that causes COVID-19 would become the fifth endemic seasonal coronavirus, alongside four other human coronaviruses. [5] A February 2023 review of the four common cold coronaviruses concluded that the virus would become seasonal and, like the common cold, cause less severe disease for most people. [11]

As of 2023 it was thought a transition to endemic COVID-19 could take years or decades. [2]

Determinants

The largest determinant of how endemicity manifests is the level of immunity people have acquired, either as a result of vaccination or of direct infection. [1] The severity of a disease in an endemic phase depends on how long-lasting immunity against severe outcomes is. If such immunity is lifelong, or lasts longer than immunity against re-infection, then re-infections will mostly be mild, resulting in an endemic phase with mild disease severity. [1] In other existing human coronaviruses, protection against infection is temporary, but observed reinfections are relatively mild. [1]

Status as an endemic disease requires a stable level of transmission. Anything that could affect the level of transmission could determine whether the disease becomes and remains endemic, or takes another path. These factors include but are not limited to: [9]

Many of the factors that determine whether COVID-19 becomes endemic are not unique to COVID-19. [9]

Global status

On 5 May 2023, the WHO declared that the pandemic was no longer a public health emergency of international concern. The WHO's Director-General, Dr. Tedros Adhanom Ghebreyesus, stated that the pandemic's downward trend over the preceding year "has allowed most countries to return to life as we knew it before COVID-19", though cautioning that new variants could still pose a threat and that the conclusion of the current state of emergency did not mean that the COVID-19 is no longer a worldwide health concern. [12] [13] [14]

Culture and society

According to historian Jacob Steere-Williams, what endemicity means has evolved since the 19th century, and the desire to label COVID-19 as being endemic in early 2022 was a political and cultural phenomenon connected to a desire to see the pandemic as being over. [3]

Paleovirologist Aris Katzourakis wrote in January 2022 that the word endemic was one of the most misused of the COVID-19 pandemic. [15] A 2023 editorial on endemicity in the International Nursing Review journal said that "Traps for unwary politicians and commentators include statements on scientific matters that fall well outside their knowledge and experience, and the danger of adopting and misusing esoteric terminology that has nuanced meanings within professional circles." [16]

When COVID-19 emerged, most people were unfamiliar with the term endemic. [17] Although the representations of endemic COVID-19 in English-language media reports were decidedly negative during the early weeks of the pandemic, since then, the concept of endemicity has been represented in the media as a positive outcome. [17] English-language media coverage, using endemic more like a buzzword to change the public's view of COVID-19 than according to a strict scientific definition, anchored the concept of endemic COVID-19 to seasonal influenza. [17] By December 2021, endemicity was being represented in media as an opportunity that people should seize to "live with the virus" and achieve a "new normal". [17] People were being told that endemicity was a desirable outcome that would achieve not only actual endemicity (a stable, predictable number of infections), but that would also bring them familiar seasonal patterns of infection, manageable demands on healthcare, and a less virulent, relatively harmless disease. [17]

Media coverage has also objectified endemicity through the metaphor of a journey, especially as the destination at the end of "the path to normality". [17]

See also

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<span class="mw-page-title-main">Pandemic</span> Widespread, often global, epidemic of severe infectious disease

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 number of individuals. 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.

<span class="mw-page-title-main">Epidemic</span> Rapid spread of disease affecting a large number of people in a short time

An epidemic is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.

<span class="mw-page-title-main">SARS</span> Disease caused by severe acute respiratory syndrome coronavirus

Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the virus SARS-CoV-1, the first identified strain of the SARS-related coronavirus. The first known cases occurred in November 2002, and the syndrome caused the 2002–2004 SARS outbreak. In the 2010s, Chinese scientists traced the virus through the intermediary of Asian palm civets to cave-dwelling horseshoe bats in Xiyang Yi Ethnic Township, Yunnan.

<span class="mw-page-title-main">Coronavirus</span> Subfamily of viruses in the family Coronaviridae

Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the common cold, while more lethal varieties can cause SARS, MERS and COVID-19. In cows and pigs they cause diarrhea, while in mice they cause hepatitis and encephalomyelitis.

<span class="mw-page-title-main">Basic reproduction number</span> Metric in epidemiology

In epidemiology, the basic reproduction number, or basic reproductive number, denoted , of an infection is the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection. The definition assumes that no other individuals are infected or immunized. Some definitions, such as that of the Australian Department of Health, add the absence of "any deliberate intervention in disease transmission". The basic reproduction number is not necessarily the same as the effective reproduction number , which is the number of cases generated in the current state of a population, which does not have to be the uninfected state. is a dimensionless number and not a time rate, which would have units of time−1, or units of time like doubling time.

<span class="mw-page-title-main">Endemic (epidemiology)</span> Disease which is constantly present in an area

In epidemiology, an infection is said to be endemic in a specific population or populated place when that infection is constantly present, or maintained at a baseline level, without extra infections being brought into the group as a result of travel or similar means. The term describes the distribution (spread) of an infectious disease among a group of people or within a populated area. An endemic disease always has a steady, predictable number of people getting sick, but that number can be high (hyperendemic) or low (hypoendemic), and the disease can be severe or mild. Also, a disease that is usually endemic can become epidemic.

<span class="mw-page-title-main">Human coronavirus NL63</span> Species of virus

Alphacoronavirus amsterdamense is a species of coronavirus, specifically a Setracovirus from among the Alphacoronavirus genus. It was identified in late 2004 in patients in the Netherlands by Lia van der Hoek and Krzysztof Pyrc using a novel virus discovery method VIDISCA. Later on the discovery was confirmed by the researchers from Rotterdam. The virus is an enveloped, positive-sense, single-stranded RNA virus which enters its host cell by binding to ACE2. Infection with the virus has been confirmed worldwide, and has an association with many common symptoms and diseases. Associated diseases include mild to moderate upper respiratory tract infections, severe lower respiratory tract infection, croup and bronchiolitis.

An emergent virus is a virus that is either newly appeared, notably increasing in incidence/geographic range or has the potential to increase in the near future. Emergent viruses are a leading cause of emerging infectious diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics. As well as causing disease, emergent viruses can also have severe economic implications. Recent examples include the SARS-related coronaviruses, which have caused the 2002–2004 outbreak of SARS (SARS-CoV-1) and the 2019–2023 pandemic of COVID-19 (SARS-CoV-2). Other examples include the human immunodeficiency virus, which causes HIV/AIDS; the viruses responsible for Ebola; the H5N1 influenza virus responsible for avian influenza; and H1N1/09, which caused the 2009 swine flu pandemic. Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.

A breakthrough infection is a case of illness in which a vaccinated individual becomes infected with the illness, because the vaccine has failed to provide complete immunity against the pathogen. Breakthrough infections have been identified in individuals immunized against a variety of diseases including mumps, varicella (Chickenpox), influenza, and COVID-19. The characteristics of the breakthrough infection are dependent on the virus itself. Often, infection of the vaccinated individual results in milder symptoms and shorter duration than if the infection were contracted naturally.

Immunization during pregnancy is the administration of a vaccine to a pregnant individual. This may be done either to protect the individual from disease or to induce an antibody response, such that the antibodies cross the placenta and provide passive immunity to the infant after birth. In many countries, including the US, Canada, UK, Australia and New Zealand, vaccination against influenza, COVID-19 and whooping cough is routinely offered during pregnancy.

Novel coronavirus (nCoV) is a provisional name given to coronaviruses of medical significance before a permanent name is decided upon. Although coronaviruses are endemic in humans and infections normally mild, such as the common cold, cross-species transmission has produced some unusually virulent strains which can cause viral pneumonia and in serious cases even acute respiratory distress syndrome and death.

<span class="mw-page-title-main">COVID-19 pandemic</span> Pandemic caused by SARS-CoV-2

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), began with an outbreak of COVID-19 in Wuhan, China, in December 2019. It spread to other areas of Asia, and then worldwide in early 2020. The World Health Organization (WHO) declared the outbreak a public health emergency of international concern (PHEIC) on 30 January 2020, and assessed the outbreak had become a pandemic on 11 March.

<span class="mw-page-title-main">SARS-CoV-2</span> Virus that causes COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the provisional name 2019 novel coronavirus (2019-nCoV), and has also been called human coronavirus 2019. First identified in the city of Wuhan, Hubei, China, the World Health Organization designated the outbreak a public health emergency of international concern from January 30, 2020, to May 5, 2023. SARS‑CoV‑2 is a positive-sense single-stranded RNA virus that is contagious in humans.

<span class="mw-page-title-main">COVID-19</span> Contagious disease caused by SARS-CoV-2

Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. The first known case was identified in Wuhan, China, in December 2019. Most scientists believe the SARS-CoV-2 virus entered into human populations through natural zoonosis, similar to the SARS-CoV-1 and MERS-CoV outbreaks, and consistent with other pandemics in human history. Social and environmental factors including climate change, natural ecosystem destruction and wildlife trade increased the likelihood of such zoonotic spillover. The disease quickly spread worldwide, resulting in the COVID-19 pandemic.

<span class="mw-page-title-main">COVID-19 vaccine</span> Vaccine against SARS-CoV-2

A COVID‑19 vaccine is a vaccine intended to provide acquired immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID‑19).

<span class="mw-page-title-main">Arnold Monto</span> American physician and epidemiologist

Arnold Monto is an American physician and epidemiologist. At the University of Michigan School of Public Health, Monto is the Thomas Francis, Jr. Collegiate Professor Emeritus of Public Health, professor emeritus of both epidemiology and global public health, and co-director of the Michigan Center for Respiratory Virus Research & Response. His research focuses on the occurrence, prevention, and treatment of viral respiratory infections in industrialized and developing countries' populations.

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<span class="mw-page-title-main">Transmission of COVID-19</span> Mechanisms that spread coronavirus disease 2019

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<span class="mw-page-title-main">Public health mitigation of COVID-19</span> Measures to halt the spread of the respiratory disease among populations

Part of managing an infectious disease outbreak is trying to delay and decrease the epidemic peak, known as flattening the epidemic curve. This decreases the risk of health services being overwhelmed and provides more time for vaccines and treatments to be developed. Non-pharmaceutical interventions that may manage the outbreak include personal preventive measures such as hand hygiene, wearing face masks, and self-quarantine; community measures aimed at physical distancing such as closing schools and cancelling mass gathering events; community engagement to encourage acceptance and participation in such interventions; as well as environmental measures such surface cleaning. It has also been suggested that improving ventilation and managing exposure duration can reduce transmission.

References

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