AMNA NAWAZ: Last fall, President Biden said the pandemic was over.

And judging by how most Americans are living their lives, they agree.

That's even though this virus is still killing about 2,000 Americans every single week.

As William Brangham reports, a much broader impact is being borne by the untold millions who survived their infection, but now suffer from the troubling chronic condition of long COVID.

WILLIAM BRANGHAM: The specter of long COVID, with its mysterious cause, no obvious cure, and an unknown duration, haunts millions of people.

In a moment, we will hear from someone who treats this puzzling condition.

But, first, let's hear from some of those who are suffering with it.

MALCOLM BROOKS, New York: One day, I woke up and I felt like I had the flu.

Like, I just had body aches and congestion and everything.

And it wasn't too bad.

It just -- it kind of felt like a flu that I have had before.

So I didn't think anything of it.

And then, as the weeks went by, I started to notice, like, the symptoms were not going away.

MICHELLE LEWIS, Florida: Physically, long COVID has absolutely just ruined my life.

I mean, it really has.

There's no other way to say that.

Many days, I still can't even get out of bed.

I now have chronic migraines.

I can't walk very far at all without running out of breath.

I'm constantly getting dizzy.

I'm constantly having to go to the E.R.

because I have fallen somewhere.

My joints hurt all the time, all the time.

That's something that people don't realize is just how much pain is involved in long COVID.

EMILY WINSON, Ohio: After having COVID the first time and recovering fine, I assumed that having it again wouldn't be a problem, because I had been OK during my first infection.

And I couldn't have been more wrong.

Now I have these debilitating symptoms.

And there's no treatment and no cure for it.

And doctors don't know what to do with you.

CHARLIE MCCONE, California: I worked through it the first year-and-a-half.

It was just brutal.

The only thing I could do was work.

And then the rest of the day, I was just pretty much out cold.

And then I got reinfected in September of 2021 with Delta.

And, for most of last year, I just couldn't get off the couch.

KARINA GONZALEZ, Texas: I even started to have a heart attack symptoms.

But, fortunately, nothing happened to me.

But I did end up going to the E.R.

because I was really scared.

I didn't know what was going on.

I had never experienced any of these symptoms before ever in my life.

And, basically, my experience was that, every time I would go to doctors or to the hospital, they would just tell me, oh, no, you're fine.

CHARLIE MCCONE: I have tried dozens of medications.

I have tried dozens of therapies.

And I went through dozens of doctor.

I finally have a great team of doctors who believe me and are doing everything they can to treat me, but I'm still completely housebound.

EMILY WINSON: All my testing I have had shows that there's no damage or anything like that, even though I have shortness of breath and chest pain pretty much every day.

And so that's probably like one of the most frustrating parts, is that doctors just don't know what to do with you.

MICHELLE LEWIS: Financially, this has been devastating.

My husband is now my full-time caretaker.

He can't really leave me alone for very long amounts of time, because I tend to fall.

So we don't have our business anymore.

If it was not for the help of friends and family and the community, we wouldn't be able to survive at all.

KARINA GONZALEZ: I am able to walk now, but I'm not able to do any exercise.

So -- and even just the thought of getting a job, I wish I could get a job.

I wish I could work.

I wish I could live a life like most other able-bodied people.

CHARLIE MCCONE: I ran out of short-term disability.

I cannot work.

I'm running out of money.

And I -- the social worker I just talked to said, don't even bother applying for long-term disability because you're going to get denied.

And so what are people in my position supposed to do?

MALCOLM BROOKS: My friends or family have been very supportive.

And that's been very helpful, but to just kind of watch your life go down the drain is very depressing.

People do not understand, if you get long COVID, and especially if it, like, debilitates you to the degree that it's done to me, you're done for.

Like, there's nothing -- there's nothing -- there's no help coming your way.

WILLIAM BRANGHAM: So that is just a small snapshot of the kinds of varied symptoms that people are dealing with right now.

For more on this, we are joined by David Putrino.

He's a neuroscientist and physical therapist.

And he's director of rehabilitation innovation at the Mount Sinai Health System.

And he joins us from his home in New York.

David, thank you so much for being here.

You heard those voices of people and what they are struggling with.

Do those stories sound familiar to the kinds of people that you deal with every day?

DAVID PUTRINO, Mount Sinai Health System: Yes, sadly, this is a very common story.

This is what we're hearing in our clinic every day.

Unfortunately, my team, since the pandemic began, we have seen over 3,000 people with long COVID.

And what I just heard is a very, very good representation of what we're dealing with every single day.

WILLIAM BRANGHAM: In a recent commentary that you co-authored in "The Lancet," you noted that -- quote -- "There are more than 200 reported symptoms associated with long COVID affecting virtually every organ system."

Given that, are there proven treatments that help?

And how do you go about helping people who are suffering from such a myriad of symptoms?

DAVID PUTRINO: It's a great question.

And it's a question that we're still working out as we go.

The reality is, long COVID is a subset of conditions.

It's a number of different conditions that have been caused by an acute viral infection.

And so we take a lot of care in our clinic to understand what subtype of long COVID we're looking at when we evaluate each patient.

And based on those subtypes, we offer different treatments for symptom management, because, right now, although we're learning a little bit about how the body is responding to the viral infection -- and, hopefully, that will lead us to some targeted therapies that we can apply -- all we can do right now is symptom management.

And we can do a good job of that.

We can make people feel a lot better with the symptoms that they have.

But we're not curing them.

We're getting them to a point where they may be a little more functional, they may be able to leave the house, but the underlying cause is still there with them.

WILLIAM BRANGHAM: That is just such a distressing diagnosis to give to people.

I know that the National Institutes of Health has a billion-dollar project looking at research into this.

What does the best research tell us as to why this is happening to people?

DAVID PUTRINO: Right now, there's a lot of uncertainty about the underlying causes of long COVID.

But what we know for sure is that long COVID is an organic disease.

So, we understand that the virus has really changed things within the body.

Now, there are three or four different ways that the virus can change the body's physiology and start to lead into the symptoms that we're experiencing with long COVID.

But what we understand very clearly is that this is not a psychological illness.

This is not a psychosomatic illness.

This is an illness that has been caused by the body responding to a previously unknown virus.

The immune system has become very dysregulated as a result of the virus, and it's leading to these highly debilitating symptoms.

I'm really optimistic that we have the potential to close in on some biomarkers and some therapies for people with long COVID.

But we need much more attention to the problem.

We need the public to understand that dying is not your only risk of serious life-changing effects from having an acute COVID infection.

And we need the government to start supporting a lot more in the way of infection prevention, so that my clinic, which is currently overwhelmed, doesn't become even more overwhelmed in the coming months and years.

WILLIAM BRANGHAM: I have to imagine that, in addition to all of the physical symptoms that people are going through, that there's got to be a great deal of just emotional distress and depression at all of the mysteries associated, as you're describing, plus this idea that much of the country seems to have moved on, while they are still very much in the middle of all this.

DAVID PUTRINO: Many people with long COVID are experiencing such a traumatic transition from previously being fully healthy, never having a serious medical condition in their entire lives, and transitioning suddenly to being completely debilitated, dependent on friends and family, as we heard in that last clip, for just basic survival.

That is a very tough transition to have to make.

And so, in our clinic, we try to do our best to make sure that, in addition to care, in addition to research that's trying to underlie -- to treat the underlying causes of the illness, we're also doing our best to provide psychological support and social support, with the understanding that this is not the underlying cause of what's going on, but the transition from non-disabled to disabled is sometimes very challenging.

WILLIAM BRANGHAM: All right, David Putrino at Mount Sinai Health, thank you so much for being here.

DAVID PUTRINO: Thank you for having me.