What Is an Endemic Virus? WHO Warns COVID-19 'May Never Go Away'
During a World Health Organization press conference Wednesday, Dr. Michael Ryan, executive director of the WHO's Health Emergencies Programme, doled out some sobering news to anyone looking for a specific end in sight for the coronavirus pandemic: There isn't one yet.
"We have a new virus entering the population for the first time, therefore it is very hard to predict when we will prevail over it," he said. And as the pandemic continues to affect millions across the world, Dr. Ryan offered up another possible future scenario: that the virus may never fully leave us.
"It's important to put this on the table: This virus may become just another endemic virus in our communities, and this virus may never go away," said Dr. Ryan. Overall, Dr. Ryan said it's important to be realistic regarding the course of the current coronavirus pandemic: "I don't think anyone can predict when or if this disease will disappear," he said.
What exactly is an endemic disease—and how is it different than a pandemic or epidemic?
In epidemiology—the study of the distribution and determinants of health-related events in specified populations—there are different levels of disease. These levels, according to the Centers for Disease Control and Prevention, essentially measure how many people have gotten sick from a specific disease, and how far it has spread:
- Sporadic: When a disease occurs infrequently and irregularly.
- Endemic: A constant presence and/or usual prevalence of a disease or infection within a geographic area. (Hyperendemic is a situation in which there are persistent high levels of disease occurrence.)
- Epidemic: A sudden increase in the number of cases of a disease—more than what's typically expected for the population in that area. (Similarly, an outbreak is in a more limited geographic area, and a cluster is an aggregation of cases grouped in place and time, suspected to be greater than usual.)
- Pandemic: An epidemic that has spread over several countries or continents, affecting a large number of people.
Right now, COVID-19 is a pandemic. The virus, which was first identified in December 2019, has currently spread to 188 countries and regions and infected more than 4,400,000 people. According to the CDC's definition of an endemic—and per Dr. Ryan's remarks in the latest press conference—COVID-19 could remain a constant presence, either around the world or in a specific geographical location or locations.
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In the most general terms, a big difference between an epidemic or pandemic and an endemic virus is predictability. In a recent interview with The Verge, Graham Medley, PhD, director of the Centre for the Mathematical Modelling of Infectious Diseases at the London School of Hygiene and Tropical Medicine, explained that fear of newness and uncertainty is often paired with epidemics or pandemics—but not necessarily endemic viruses. "For most people, the difference between epidemic disease and endemic disease is that the risks are unknown for an epidemic disease," he said. “The definition is really based on how the risks are perceived by individuals and by governments.”
Ultimately, as the newness of COVID-19 dies down—and if, in that happening, the coronavirus isn't contained or eradicated—it may end up as another endemic virus that people are somewhat regularly exposed to. That said, if COVID-19 does become an endemic virus, there's no way of knowing right now where it will be most prevalent, or what the baseline level of disease (oddly enough, also referred to as the "endemic level" of disease) would be.
What are some examples of endemic viruses?
In the WHO press conference Wednesday, Dr. Ryan used human immunodeficiency virus (HIV) as a type of endemic virus. While HIV is still technically considered a pandemic, per the CDC, Dr. Ryan says the global population has a level of awareness about the virus. "HIV has not gone away but we've come to terms with the virus and we've found the therapies and we've found the prevention methods and people don't feel as scared as they did before," he said, adding that now modern medicine is offering "long, healthy lives to people with HIV."
Malaria, per the CDC, is another example of an endemic disease in certain areas. The highest transmission rate of malaria—a serious, sometimes fatal disease caused by a parasite and transmitted by mosquitos to humans—is in parts of Africa south of the Sahara, as well as regions like Papua New Guinea. It's well-known that malaria is more prevalent in warm regions close to the equator in malaria-endemic countries, which is why travelers to those countries may need malaria-prevention medications.
There's also a chance that COVID-19 may take the route of other cold-causing coronaviruses or the seasonal flu, circulating during a few specific months of the year and subsiding during other months. While the flu isn't classified as an endemic virus, there is a level of predictability to it, and measures put in place reduce its spread (the flu vaccine) or hasten recovery time in affected individuals (antiviral medicines like Tamiflu), Medley told The Verge.
It's important to remember that the possibility of COVID-19 becoming an endemic virus is hypothetical right now. Again, there's no telling if or when the new coronavirus will be eradicated. But overall, Dr. Ryan—and presumably most other health officials—have one "great hope" for the trajectory of COVID-19: "If we do find a highly effective vaccine that we can distribute to everyone who needs it in the world, we may have a shot at eliminating this virus," he said. "But this vaccine will have to be highly effective, be made available to everyone, and we'll have to use it."
The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.
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