Millions of people who have gotten Covid-19 and survived are finding that a full recovery can be frustratingly elusive. Weeks or even months after seemingly recovering from even a mild case, many patients still confront a wide range of health problems. As researchers try to measure the duration and depth of what’s being called “ long Covid,” a growing number of specialized, post–acute Covid clinics are opening to handle the patients. The scale of the pandemic and persistence for some of Covid’s disabling effects mean the economic pain and drain on health resources could continue well after the contagion ends.

1. What are the ailments?

Fatigue, shortness of breath, chest pain, joint aches and cognitive disturbances such as “ brain fog” are commonly described problems that emerge or linger four weeks or more after an infection with SARS-CoV-2, the virus that causes Covid. The severity can range from annoying to incapacitating. Specific organ dysfunction also has been reported involving primarily the heart, lungs and brain, even among those who had no noticeable symptoms during the acute phase. Although most long Covid symptoms don’t seem to be life-threatening, a study published in April in the journal Nature found that sufferers had a 59% increased risk of dying within six months. That works out to about eight extra deaths per 1,000 Covid patients -- adding to the pandemic’s hidden toll.

2. How prevalent is it?

Researchers haven’t studied enough cases over a long enough period to gauge the full range of effects, what proportion of patients will suffer from them or for how long. Early findings and the demand for specialized clinics to help survivors deal with scarred lungs, chronic heart damage, fatigue and other conditions indicate a significant prevalence. A study released in June by researchers at Imperial College London surveyed more than half a million people. It found that 38% of those who said they’d had Covid reported at least one symptom lasting 12 weeks or more, and 15% experienced three or more symptoms. The prevalence was higher in women and increased with age. A large Danish study of people who didn’t require hospitalization found the absolute risk of severe, post-acute complications was low. But it also noted increases in general practitioner and outpatient hospital visits, which could indicate lingering symptoms.

3. Is Covid-19 definitely to blame for these symptoms?

Not necessarily. A large study based on data from a U.S. health plan published in the BMJ in May found that 14% of people infected with the coronavirus developed one or more related complications requiring medical care beyond the acute phase -- but so did 9% of people in a control group. Some symptoms might occur by chance or be triggered by stress and anxiety. A study of health-care workers at a Swedish hospital compared persistent symptoms among those who had recovered from mild Covid-19 at least 8 months before, and those who never caught the coronavirus. Among those who’d been infected, 8% reported lingering symptoms causing moderate-to-marked disruptions of their work life, compared with 4% in the non-infected group. In some critical Covid cases, life-saving treatment itself may cause problems. Such uncertainties have sometimes led to what patients describe as “ medical gaslighting” by health professionals who don’t take their complaints seriously, especially if the patient is a woman.

4. What are the broader implications?

Some researchers say the pandemic may spur a raft of long-term problems such as chronic fatigue syndrome, dementia, Parkinson’s disease, diabetes and kidney impairment. An uptick in treatments for depression, anxiety and pain has stoked concern of a spike in suicides and opioid overdoses. The U.S. Centers for Disease Control and Prevention reported a surge in overdose deaths in 2020. The reduced work hours reported in 69% of patients, colloquially known as long-haulers, indicate the pandemic is having an impact on labor productivity. With more than 175 million confirmed infections worldwide as of mid-June, even a small share with long-term debility could have enormous social and economic consequences. And these will be magnified if problems end up lasting for years or decades.

5. Do other viruses cause prolonged illness?

Yes. So-called post-viral syndromes occur after infections including the common cold, influenza, HIV, infectious mononucleosis, measles and hepatitis B. Diabetes and other long-term consequences were observed in survivors of severe acute respiratory syndrome (SARS), which is caused by coronavirus related to SARS-CoV-2. A Canadian study identified 21 health-care workers from Toronto who had post-viral symptoms for as long as three years after catching SARS in 2003 and were unable to return to their usual work. Some people who were hospitalized with SARS in Hong Kong still had impaired lung function two years later, a study of 55 patients published in 2010 found. Still, it’s not known yet whether the lessons of SARS are applicable to Covid-19.

6. What is being done?

In the U.S., Congress is providing some $1.15 billion in funding over four years for the National Institutes of Health to support research into the long-term effects of Covid. The studies hopes to get at issues such as the underlying biological causes and how they might be treated and prevented. Some researchers are pressing governments to focus attention not only on infection and vaccination rates but on potential long-term organ damage. For example, researchers have shown the virus can infect insulin-producing pancreatic tissue, potentially triggering diabetes that in some cases persists beyond the acute infection. That’s prompted Australia’s Monash University and King’s College London to create a global registry for studying “new onset” diabetes. Some long haulers have reported feeling better after receiving a Covid vaccination, prompting researchers to examine the phenomenon and whether vaccines can offer clues to treatment. Avindra Nath, clinical director of the U.S. National Institute of Neurological Disorders and Stroke, said vaccines, including for flu, have been known to help patients with chronic fatigue, but relief has almost always been temporary.

The Reference Shelf

• Related QuickTakes on what you need to know about the virus, how it spreads, the impact on kids, the risk of second waves, the quest for vaccines and treatments, and how safe is flying.
• NIH Director Francis Collins tries to make sense of long Covid syndrome in a blog post.
• The World Health Organization answers commonly asked questions about Covid-19.
• An app that records daily symptoms developed at King’s College London tracks more than 4 million Covid-19 patients in the U.K., Sweden and the U.S.
• Support groups on Slack and Facebook share experiences of thousands of long haulers, and the Journal of the American Medical Association looked at their stories too.