Here’s what we know about long Covid — with some hope for the future.

Authors: By German Lopez  Aug 30, 2021, 8:30am EDT

Over the past few months, experts and officials have tried to prepare the world for a future in which Covid-19 is here to stay. They predict the vaccines will by and large defang the virus. There will still be a few cases of serious illness and death, but the coronavirus will be reduced to the level of a seasonal flu — a disease we’d be much better off without, but mild enough we won’t shut down society to fight it.

But this optimistic vision has always left open a big question: What about long Covid?

Covid-19 is most known for causing acute illness, from a cough and fever to hospitalization and death. But in some cases it seems to cause longer-term complications, including breathing difficulties, fatigue, and brain fog, though the effects vary from person to person. While Covid-19 typically resolves in the span of weeks, long Covid can last at least months after an infection.

“Without treatment, we’ve seen individuals who got sick in February or March of 2020 and are still sick and still extremely debilitated,” David Putrino, who’s treated long Covid patients at the Mount Sinai Health System in New York, told me.

These long-term complications aren’t unique to the coronavirus; other viruses, including seasonal flu, cause long-term symptoms too, sometimes similar ones. But as more people have been infected by the coronavirus, and more have subsequently developed long Covid, the long-term problems have received more attention.

So even in the context of a post-vaccine world, does long Covid makes the coronavirus too dangerous to live with? Can the world really treat Covid-19 like a flu-level illness if it’s causing debilitating long-term problems for many?

The truth is there’s still a lot about long Covid we simply don’t know. We don’t know what causes it, or why some people seem to develop long Covid symptoms while others don’t. We don’t know with much precision how often long Covid occurs. We don’t know how variants of the virus, including delta, have altered the risk. We don’t even know if all the cases believed to be long Covid are actually caused by the coronavirus.

Nor do we know much about breakthrough cases among vaccinated people leading to long Covid, though we know there have been some cases. But the vaccines very likely help to prevent long Covid by reducing both the likelihood of infection and severity of illness, both of which are associated with long-term complications. “If you’re not getting infected with Covid, you’re not going to get long Covid,” Putrino said.

The uncertainty makes it difficult to make any kind of sweeping declarations about long Covid. Based on my conversations with experts, the best we can say goes something like this: Long Covid is relatively rare, especially among vaccinated people. And it will likely become rarer over time, especially as more people get vaccinated and the population in general develops stronger immune defenses against the coronavirus.

“The hope is that over time as more variants emerge, as we keep getting more booster vaccinations, [and] as our body becomes more accustomed to producing antibodies to this virus type, we’re going to see cases of long Covid reducing — to the point where it’s not really a thing anymore,” Putrino said. But he cautioned, “This is conjecture. We don’t know for sure.”

It’s helpful, then, to view long Covid through two lenses: what the outlook is right now, in August 2021, and what it might look like in a few months or years. How worried you should be today if you’re vaccinated depends, like many things in the pandemic, on your own risk tolerance. But in the long term, there are some hopeful signs.

What long Covid looks like now

There are some things about long Covid we do know. It’s a real medical problem, although its symptoms, severity, and duration vary from person to person. These symptoms aren’t permanent in all cases — potentially not any of them — but they can last for a year or more. And some treatments, part of a nascent and growing field of medicine, can potentially cut down the symptoms’ severity and duration.

Most cases of Covid-19 don’t lead to long Covid. The limited data so far suggests 10 to 25 percent of adults infected with Covid-19 might develop long Covid (although experts advise a lot of caution in interpreting those numbers since the data here isn’t of great quality).

While we don’t know what causes long Covid, there are some theories — all speculative for now. One possibility is that lingering reservoirs of the virus or fragments of it continue to wreak havoc in the body. Another is that long Covid is part of the body’s healing process after fighting off the coronavirus. Yet another is that, because the SARS-CoV-2 virus is novel to humans, it can lead to a long-lasting overreaction by the immune system.

A major unknown is if all the detected long Covid cases are even caused by the coronavirus, given that some of the people who present long-term symptoms test negative for Covid-19 and related antibodies. Experts don’t deny that the symptoms are real and should be treated, but it’s also possible psychosocial circumstances or other pathogens could be behind some cases.“THE PROBLEM IS THAT WE KNOW VERY LITTLE ABOUT HOW FREQUENTLY BREAKTHROUGH INFECTIONS LEAD TO LONG COVID” —AKIKO IWASAKI

Many viruses, like seasonal flu, can cause long-hauler symptoms. One study in Pathogens suggested some long Covid cases may be due to reactivations of the Epstein-Barr virus that causes mononucleosis. (When I was in high school, I lost months to fatigue due to recurring mono.) So some people showing up at the doctor’s office with long Covid could have “long flu,” mono, or another disease entirely. “It’s hard to say,” Putrino acknowledged.

Long Covid remains a unique threat right now for two reasons: There’s still a lot of coronavirus out there, as the country deals with a recent surge driven by the delta variant. And compared to pathogens like the flu, fewer people have immune defenses built up against the virus, likely boosting the chances of developing Covid-19 and then long Covid compared to the risk of suffering long-term complications from the flu.

The good news: These risks can be mitigated with vaccines.

The vaccines cut the chances of getting infected by the coronavirus in the first place. To the extent long Covid cases are caused by the virus, that means fewer cases of long Covid. The delta variant and waning efficacy have complicated this, increasing the risk someone is infected with the virus even after vaccination — potentially necessitating booster shots. But the vaccines still offer some protection against the risk of any infection.

The vaccines also offer protection against severe disease. This protection has so far held up against the delta variant and despite concerns about waning efficacy: Multiple studies have found the vaccines are still around 90 percent effective against hospitalization or worse, both during delta’s spread and months after the shots are administered. A recent study from the Centers for Disease Control and Prevention found unvaccinated people are 29 times as likely to be hospitalized with Covid-19 than fully vaccinated people.

That’s important because long Covid also seems much more likely to develop in people who had severe cases of Covid-19. A study analyzing private health care claims, by the nonprofit FAIR Health, found that hospitalized Covid-19 patients were almost twice as likely as patients who weren’t hospitalized but were symptomatic to develop “post-Covid conditions.” Patients without symptoms were even less likely to develop longer-term conditions than those with symptoms, although it did happen in some cases.

So to the extent that the vaccines make you less likely to get sick in the first place, and much less likely to get severely ill if you do get sick, they reduce your chance of getting long Covid. If you do get sick, though, there’s a lot we don’t know.

Some breakthrough infections can lead to long Covid, as one New England Journal of Medicine study tracking Israeli health care workers found. But that study also found the overall prevalence was low: Among nearly 1,500 fully vaccinated health care workers who were exposed to the coronavirus or had related symptoms, just seven, of 39 breakthrough infections, reported persistent symptoms after more than six weeks.

Still, that’s one estimate from a small study looking at a somewhat narrow time period. “The problem is that we know very little about how frequently breakthrough infections lead to long Covid,” Akiko Iwasaki, an immunologist at the Yale School of Medicine, told me.

Perhaps the best that can be said is the vaccines likely help, probably significantly, but it’s unclear just how much. Given that, and the spread of the delta variant, some experts say it makes sense for those worried about long Covid to remain cautious and mitigate exposure even after getting the vaccine (through, say, masking), at least for now.

What long Covid might look like in the future

Moving forward, there are some reasons to be hopeful about long Covid.

For one, the Covid-19 pandemic will end. Through vaccination, natural infection, or both, the population will continue to build immunity against the coronavirus. Over time, this buildup will turn into a bulwark against SARS-CoV-2 — one that may not stop the virus from spreading entirely (experts expect the virus will instead become endemic, meaning it will still circulate as illnesses like colds and the flu do), but will at least reduce the number of infections and especially cut down on the most severe outcomes, like hospitalization and death.

Those population-level defenses will mean fewer infections and less severe illness, both of which will translate to fewer cases of long Covid over time.

Putrino offered an optimistic, albeit speculative, possibility: If long Covid is caused by an overreaction from an undeveloped immune system to a novel coronavirus, then the steady buildup of immunity and continued exposure to the virus over time could help reduce the risk of long Covid. In that case, the remaining incidents of Covid-19 as the virus turns endemic may be less likely to lead to long Covid.

“We need to focus on being a little more patient,” Putrino argued. “A year and a half feels like a long time. But in terms of how long it takes for our bodies to change and adapt to things, it’s a very short amount of time.”

We’ll also hopefully learn much more about long Covid going forward. That may help with prevention, such as techniques or treatments to stop Covid-19 from leading to long Covid. It could also help with the treatment of long Covid, potentially reducing its severity or duration. (Developing such treatments, though, will require taking long Covid seriously — something medical and research communities haven’t done in the past with “long haulers” dealing with other diseases.)

Over time, a waning pandemic and the reduced risk of getting Covid-19 could help us live with the virus, including with the possibility of long Covid. Just like people have learned to live with the flu and the severe outcomes it can cause (including long-term health complications and tens of thousands of deaths a year in the US), so too will people learn to live with a Covid-19 that’s weakened by the vaccines and natural immunity.

As is true with the flu or anything else in life, different individuals have different risk tolerances. Some people may choose to go out less during periods in which cases rise, continue to wear masks, or seek out booster shots. Others may decide the low chances of complications after they get a vaccine, if they even decide to get the shot, are tolerable enough to continue living as normal, even when cases rise within their community. Many will fall in between.

“Some people will do everything possible to prevent their risk, and other people will not worry as much,” Céline Gounder, an epidemiologist at New York University, told me. “It’s going to depend on the person.”

So the solution to long Covid may look a lot like the other scary, uncertain things about the pandemic, from variants to breakthrough cases: There’s no perfect option, but the best we can do is get as many people vaccinated as possible to defang the coronavirus — and greatly reduce the risk of long Covid — even if it’s never truly eliminated.