What It Means for a Pandemic Like Covid to Become ‘Endemic’ – The New York Times

For months, some American and European leaders have foretold that the coronavirus pandemic would soon become endemic. Covid-19 would resolve into a disease that we learn to live with. According to several governors, it nearly has.

But we are still in the acute phase of the pandemic, and what endemic Covid might look like remains a mystery. Endemic diseases can take many forms, and we do not know yet where this two-year-old disease will fall among them.

40 cases per day

per 100,000

March 2020

W.H.O. declares

Covid-19 a pandemic

40 cases per day

per 100,000

March 2020

W.H.O. declares Covid-19

a pandemic

Sources: Local governments; Center for Systems Science and Engineering at Johns Hopkins University; National Health Commission of the Peoples Republic of China; World Health Organization Note: Data is as of April 5. Chart shows seven-day average.

At its most basic, an endemic disease is one with a constant, predictable or expected presence. Its a disease that persists. Beyond that, there is no fixed definition.

Endemic diseases infect millions of people around the world each year, and some endemic diseases kill hundreds of thousands. Some we can treat and vaccinate against. Yet they can also cause unexpected outbreaks and significant suffering.

Interviews with two dozen scientists, public health experts and medical historians suggest the rush to recast Covid as endemic may be missing the point.

Theres been a political reframing of the idea of endemic as something that is harmless or normal, said Lukas Engelmann, a historian of medicine and epidemiology at the University of Edinburgh. But epidemiologists use endemic to mean something we should watch carefully, he said, because an endemic disease can become epidemic again.

Endemic diseases can be mild or deadly

When people think of endemic disease, they often think of the common cold. Upper respiratory infections, including colds, are estimated to infect billions of people worldwide every year but kill several thousand. Other endemic diseases can be much more lethal. Malaria killed more than 600,000 people globally in 2019, and flu killed more than 200,000, though estimates suggest these tolls could be much higher.

New global cases per 100,000 in 2019

New global deaths per 100,000 in 2019

New global cases per 100,000 in 2019

New global deaths per 100,000 in 2019

Many scientists predict that endemic Covid may have a similar burden to other respiratory viruses.

It will be no more deadly than seasonal flu, or may be mild like one of the cold-causing coronaviruses, said Lone Simonsen, the director of the PandemiX Center at Roskilde University in Denmark.

The reason for this is that we have a lot of immunity and we keep getting boosted from the infections that we run into, she said.

Some scientists warn that immune protection from vaccination and infection may wane over time, and future variants might sidestep those defenses. And mutations are random, so there is always a chance a variant that causes more severe disease could arise in the future.

Endemic diseases can have epidemic periods

The common cold and the flu are widespread endemic diseases that persist year round, but their levels are not constant. Instead they cause seasonal epidemics, where infections rise beyond baseline endemic levels, often in the winter when people gather indoors.

2020

Covid-19

policies

disrupt spread

2020

Covid-19

policies

disrupt

spread

These patterns are predictable, but people can change them: The control measures used to blunt the Covid pandemic dampened flu and cold waves in recent years, too.

Scientists say that endemic Covid could be seasonal, but it could also have irregular and significant epidemic waves.

Covid is much, much more transmissible than the flu, said Jeffrey Shaman, an infectious-disease modeler at Columbia University. Only a small portion of the population needs to be susceptible for an outbreak to foment, and that can happen at any time of year.

The burden of endemic disease is unequal

One communitys experience with endemic disease can be vastly different from anothers, often depending on who is getting sick and whether they have access to tests, treatments and health care.

H.I.V., which has persisted across the globe for more than 40 years, is one example, though scientists and public health workers use both epidemic and endemic to describe the virus.

One definition of endemic is defined by geographic location, said Dr. Diane Havlir, an infectious disease specialist and professor of medicine at the University of California, San Francisco. Through that lens, H.I.V. is endemic in the United States, where approximately 1.2 million persons are living with H.I.V.

But H.I.V. is epidemic in subpopulations in the U.S., she added.

Changes in data methodology

Changes in data methodology

Infectious diseases often remain in communities where poverty or discriminatory systems prevent access to health care, Dr. Havlir said.

Disease disparities increase over time unless they are addressed at the outset, she said. And that raises the question: Are we addressing those disparities with Covid or are we on that same trajectory?

With one-third of the global population unvaccinated against Covid and life-saving treatments not available to all, the viruss burden will likely continue to be unequal, experts say, even as parts of the world decide their levels are endemic.

Endemic disease is all about control

Among the many forms endemic disease can take, one thing is clear: Endemic does not mean the end of the disease.

Instead, it means living with, and often managing, a disease that has not been, or cannot be, stamped out. Health experts say that countries must use control measures, like testing, treatments and vaccinations, to keep endemic diseases in check.

Countries with endemic malaria aspire to eradicate the mosquito-borne disease and rely on interventions like insecticides and preventative treatments to reduce its incidence. These control measures can drastically alter the course of endemic malaria, as they have in South Africa.

2000 epidemic

DDT use resumes

2001

New treatment

introduced

2000 epidemic

DDT use resumes

2001

New treatment

introduced

In addition to environmental controls, vaccination programs can reduce cases and deaths. But when communities do not adhere to vaccination recommendations, outbreaks can happen.

Measles, for example, remained endemic in the United States for 40 years after the introduction of vaccines. During that period, unvaccinated people remained vulnerable, fueling occasional outbreaks. In 2019, two decades after the disease was declared eliminated in the United States, several outbreaks, many associated with unvaccinated travelers, infected more than a thousand people.

1963

Measles vaccine

licensed in U.S.

1989

Many measles

outbreaks

2000

Measles declared

eliminated in U.S.

1963

Measles vaccine

licensed in U.S.

2000

Measles declared

eliminated in U.S.

1989

Many measles

outbreaks

Unlike malaria or measles, public health experts say that Covid cannot be eradicated, so control measures will help determine the size and course of future waves. (We have eradicated just one human disease: smallpox, which behaved quite differently from Covid.)

Keeping up with Covid means staying focused on vaccinating, treating and updating vaccines, said Dr. Monica Gandhi, an infectious disease specialist and professor of medicine at the University of California, San Francisco. Its going to take constant vigilance to keep it not to eradicate it, which would be what humans want but to keep it under control.

When will we know what Covids endemic phase looks like?

Probably not for a while. Scientists usually determine a diseases endemic pattern after observing it for many years.

Pandemics can take years to settle, and the consequences of widespread illness can last long after new infections fade.

Much of what we know about the transition out of pandemics comes from flu humans have witnessed four influenza pandemics in the last 100 years. The 1918-19 pandemic, which killed more than 50 million people globally, dwarfs them all.

195758

and 1968

pandemics

Change in data methodology

Change in data methodology

195758

and 1968

pandemics

Change in data

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What It Means for a Pandemic Like Covid to Become 'Endemic' - The New York Times