Below is a complimentary Demography Unplugged research note written by Hedgeye Demography analyst Neil Howe. Click here to learn more and subscribe.

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According to a new study, about a quarter of patients who recovered from Covid-19 later sought medical treatment for new health problems. "Long Covid," spanning a wide variety of syndromes, afflicts a large share of recovered patients, including one in five of those who reported no symptoms when infected. (The New York Times)

NH: New studies are gradually expanding our understanding of Long Covid. As I've pointed out before, chronic illnesses suffered by post-acute Covid-19 patients are likely to generate additional visits to healthcare providers--and pose significant costs to the U.S. economy--for years to come. (See "COVID-19 Pandemic Update" on 11/12/20 and, most recently, "Demography Q&A" on 5/6/21)

The study described in this NYT story, by a research nonprofit with access to U.S. private insurance claims data (FAIR Health), has one great strength: gigantic n-size.

It selected the claims records for nearly 2 million Americans who tested positive for Covid-19 between February and December of 2020 and then examined what happened to them later.

Verdict: 23% of positives came back to see a provider for a Covid-related condition more than 30 days after their test--the most common definition of "Long Covid." The rate was certainly higher for the 5% of positives who ended up hospitalized for Covid (50%) than for the 40% with only mild symptoms (27%). Yet the rate was substantial even for the 50%+ of positives who were asymptomatic (19%).

This 23% is consistent with a more rigorous statistical analysis conducted by Washington University researchers of positives within the Veterans Health Administration. This sample was also quite large (n=73K). The researchers compared it to a control group that was statistically created to be identical to the positives, except for the fact that the controls did not test positive.

Their result: Positives (more than 30 days after test) were 20% more likely to require outpatient care at any time and had 47% more provider encounters in any 30-day period.

These percentages may underestimate the magnitude of Long Covid since many people can experience debilitating symptoms and still not see a doctor--especially for "soft" symptoms like fatigue, anxiety, depression, confusion, and insomnia.

A large, survey-based study of positives in California and Nevada found that 42% reported at least one Long Covid symptom after 30 days and 24% did so after 90 days. Long Covid after 90 days is a more durable problem because at that point symptom prevalence decays much more slowly.

The newer and larger studies may begin to narrow the wide range of estimates of just what that prevalence is. While WHO's most recent advisory issued in February offers a low figure (10%) for symptoms after 12 weeks, WHO concedes that the published figures range very widely depending upon the methodology of the study. Its summary of various studies, most of them with small n sizes, demonstrates that this range is indeed all over the map.

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Which sorts of maladies does Long Covid encompass?

Almost everything under the sun, as all of the studies make clear. Victims suffer from respiratory problems (difficulty breathing, reduced lung capacity, reduced O2 diffusion); metabolic disorders (insulin resistance, high blood lipids; anemia; liver and kidney damage); cardiovascular issues (hypertension, rapid heartbeat, cardiac inflammation, clotting); digestive complaints (abdominal pain, nausea, gastric issues); nervous system disorders (severe headache, body aches, "brain fog"); and overall emotional and physical distress (chronic fatigue, anxiety, depression).

How long does Long Covid last? Due to the bewildering multitude of symptoms--and to the fact that some symptoms may get worse even while others get better--no one yet has a clear idea. The general consensus (see also here) is that the prevalence declines steadily from 30 days after infection to 90 days (3 months), but that symptoms thereafter stubbornly resist much decline.

The most exhaustive study to date on Long Covid's trajectory (global, with n=3,762) concludes that the afflicted are clustered into separate groups, and that those not recovered within 3 months present with a distinct mix of "moderate" symptoms that persist over time.

This group "indicated that fatigue, breathing issues, and cognitive dysfunction (i.e., 'brain fog') were the most debilitating of symptoms."

Who is most likely to experience Long Covid? As I already mentioned, the likelihood goes up for those who suffer more serious symptoms during the acute infection. But recall: Even those who are asymptomatic after testing positive have a 19% risk of Long Covid--not that much lower than the 27% who are symptomatic but not hospitalized. There is also evidence that women (by gender) and whites (by race) are somewhat more likely to experience Long Covid.

Most of all, let me stress this: It is very clear that youth does not protect you from Long Covid. In fact, the risk may go down slightly at older ages. Most researchers say the most at-risk age range is 35 to 49, and positives in their late teens and 20s are probably more at risk than positives in their 70s and 80s.

Here's an age breakdown of perhaps the largest national survey of Long Covid symptoms, run by UK's Office of National Statistics (ONS). Note that the prevalence rate peaks at ages 35 to 49.

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Several theories have been suggested to explain why the age profile of severe chronic Covid differs so much from that of severe acute Covid. One is survivor bias: An infection severe enough to kill someone past age 70 may allow that same person to survive at age 40--but suffer longer-term symptoms.

Another is based on the premise that Long Covid constitutes a post-infection auto-immune disorder (just as Chronic Fatigue Syndrome, which also occurs in women more than men, is often assumed to be a post-influenza auto-immune disorder). In younger people with more active immune systems, the disorder would therefore tend to be more severe.

I stress the undiminished risk of Long Covid among younger age brackets, because the dominant reason young adults offer for not getting vaccinated is their worries about vaccine side-effects.

Young adults often perceive the risk of vaccine side effects to be large compared to the danger they face from Covid-19 itself.

True enough: The young adult's risk of dying from Covid-19 is very small--though it's not nearly so small as the risk of dying from the vaccine, which is statistically indistinguishable from zero.

In the Moderna trial, within seven weeks after the second dose, one more person actually died in the placebo group (from Covid-19) than in the vaccine group, with both numbers reflecting the approximate odds of anyone dying over a 7-week period. Faced with such small odds either way, though, young adults can reasonably say: Hey, the odds of anything bad happening are tiny in any case, so why bother?

The young-adult risk of suffering from Long Covid, on the other hand, is quite substantial. Sooner or later, the vast majority of unvaccinated young adults will be infected.

And once they are, as we have seen, their odds of incurring Long Covid are somewhere in the range of 2 in ten to 3 in ten. The odds of a serious or long-term side effect from the vaccine by contrast is 2 or 20 or (at the outside) perhaps 200 per million. That makes the vaccine roughly 100,000X to (at worst) 1,000X less risky than Covid-19.

What's more--and this is ironic--the young are actually more likely than the old to suffer from the Long Covid syndromes that are most similar to the vaccine side effects that they most fear.

Let's consider two vaccine side effects often cited by worried young adults. The first is the rumor that vaccines trigger nervous system side effects. This may have been prompted by reports linking the J&J vaccine to Guillain-Barré Syndrome (GBS).

In fact, there probably is no linkage: The incidence of GBS following the J&J shot, 8 cases per million vaxes, is no different from the incidence in the general population (6 to 40 cases per million).

But now let's compare this with the probability of cognitive dysfunction among those afflicted by Long Covid. Nearly nine out of ten Long Covid patients report cognitive dysfunction--and the prevalence is highest in the youngest age brackets.

Let's look again at the global survey mentioned earlier. Note that the youngest adults are most likely to complain of practically every problem, from attention and problem solving to "slowed thoughts." They are also the most likely to say it interferes with their work.

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The second is the risk that a vaccine could cause heart inflammation (myocarditis or pericarditis) and rapid heartbeat. A mild, temporary rise in heartbeat for a few days is a normal reaction to the vaccine; it is also a normal reaction to an acute infection by Covid-19 (or indeed by just about any infectious virus).

But heart inflammation and longer-term heart rate problems as a result of the vaccine are rare. Some 630 instances have been confirmed after 177M vaccinations, putting the incidence at under 4 per million. I repeat: 4 per million.

Among Long Covid sufferers, however, cardio problems turn out to be very common. In the global survey, 86% of Long Covid respondents reported palpitations; 61% reported tachycardia; and 53% reported chest pain. Even after 6 months, the percentages were 40%, 34%, and 27%, respectively. 

A study of thousands of Americans with 24/7 wearable fitness trackers came to a similar conclusion. Researchers examined the records of 875 wearers through January, 2021, who reported a respiratory illness, 234 of whom reported testing positive for Covid-19. Of that 234, nearly all showed an elevated heartbeat for a few days while they were infected.

Thereafter, recovery paths diverged. Most showed a sub-normal rate for a week or two, and then gradually returned to a normal heart rate. But about 14%--the Long Haulers with cardio complications--showed a continued heart-rate elevation of more than 5 beats/minute at the end of 19 weeks (the end of the study) with little decline over the last several weeks.

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Fourteen percent is a large share. That would translate into 140,000 per million Covid positives reporting any symptoms. That's a lot more than just 4 per million, wouldn't we all agree?

And lest you imagine these are primarily older adults, here is the Fairview breakdown by age of all Long Covid sufferers who were diagnosed with cardiac inflammation. The largest share, a full quarter, was age 18 to 29.

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Let's pan out at this point and look at the broader question. What's the total magnitude of Long Covid's impact? Just how many Americans are we talking about? Let's conservatively assume 20% of all positives eventually encounter Long Covid.

As of the end of March, 2021, the CDC's best guess is that 115M Americans have been infected. By now, we can assume that the number is up to at least 130M.

That translates into about 26M Long Covid sufferers. Over time, we can assume that some of this group will get better. But we can also assume that more of the unvaccinated will get infected, adding to the group. It is also possible that "breakthrough" Delta variant infections among the vaccinated may add to the group--but we have zero data yet on this possibility

In any case, a number this large is going to be consequential. Think about the 47% rise in outpatient visits per week by Long Covid patients observed in the VA population. Then multiply that by 26M.

Or think about the impact on employment. In the global survey referenced earlier, of the 93% of Long Covid respondents who did not experience a full recovery by the end of the survey time period, 73% reported they were working on a reduced schedule due to their symptoms.

That includes 22% who reported that they were unable to work at all due to their symptoms. Again, multiply these percentages by 26M. Could this explain a lot of the missing 3M in labor force participants that I discussed on The Macro Show? I bet it could.

As a demographer, I also think about mortality. Long Covid doesn't just make you feel bad. It can kill you--though the proximate cause of death will never be identified as Covid-19.

The Washington University study demonstrated with some precision that the mortality rate among all Covid-19 positive patients during the six months after their recovery from infection (that is, after 30 days) is 59% higher than among a demographically identical group that was never infected. 

This is the extra risk for all Covid positives--not just those with Long Covid. But we can reasonably assume that the risk of death is at least that high, and probably quite a bit higher, among Covid positives who experience chronic symptoms.

As I pointed out several months ago, we shouldn't be surprised by this finding. When SARS-CoV-1 hit the world back in 2003, there was widespread astonishment at its high case mortality rate. Yet another important feature of this coronavirus was seldom remarked upon: the high rate of chronic illness ("Long SARS") among the survivors. 

According to one study of a sample of SARS survivors, 30% had not returned to work two years after their infection; and average walking speed, a good surrogate indicator of expected mortality, remained far below normal. Why would we expect Covid-19, driven by another coronavirus (SARS-CoV-2), to be all that different?

Increasingly we read news stories discussing the Covid pandemic in the past tense--as if, in the vaccinated high-income world, it's pretty much over except for the outside risk of some novel variant breakthrough. All that's left for us now is to "rebound" back to where we were before.

But Long Covid paints a different picture, of a pandemic whose shadow is much larger than its death toll. It is, in reality, a pandemic that is still oppressing tens of millions of us and that will continue to affect our families, our healthcare system, our work lives, and our economy for many years to come.

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Neil Howe is a renowned authority on generations and social change in America. An acclaimed bestselling author and speaker, he is the nation's leading thinker on today's generations—who they are, what motivates them, and how they will shape America's future.

A historian, economist, and demographer, Howe is also a recognized authority on global aging, long-term fiscal policy, and migration. He is a senior associate to the Center for Strategic and International Studies (CSIS) in Washington, D.C., where he helps direct the CSIS Global Aging Initiative.

Howe has written over a dozen books on generations, demographic change, and fiscal policy, many of them with William Strauss. Howe and Strauss' first book, Generations is a history of America told as a sequence of generational biographies. Vice President Al Gore called it "the most stimulating book on American history that I have ever read" and sent a copy to every member of Congress. Newt Gingrich called it "an intellectual tour de force." Of their book, The Fourth Turning, The Boston Globe wrote, "If Howe and Strauss are right, they will take their place among the great American prophets."

Howe and Strauss originally coined the term "Millennial Generation" in 1991, and wrote the pioneering book on this generation, Millennials Rising. His work has been featured frequently in the media, including USA Today, CNN, the New York Times, and CBS' 60 Minutes.

Previously, with Peter G. Peterson, Howe co-authored On Borrowed Time, a pioneering call for budgetary reform and The Graying of the Great Powers with Richard Jackson.

Howe received his B.A. at U.C. Berkeley and later earned graduate degrees in economics and history from Yale University.