CNN  — 

Linda Timmer wanted to practice what she preached.

While working at a domestic violence nonprofit in Arizona during the height of the Covid-19 summer wave in 2020, Timmer wrote pandemic policies for her workplace, encouraging her colleagues to wear masks and, if they had been exposed to the coronavirus or had symptoms, get tested.

Timmer herself was not aware of being exposed or having any Covid-19 symptoms, such as cough or fever, but she started experiencing some unusual moments when she felt fatigued or forgetful, along with several episodes of confusion.

“They weren’t really putting that in the list of symptoms to go get tested for,” said Timmer, now 64.

That August, “the brain confusion was so unusual for me that I just thought, ‘I’m telling everyone to wear masks and follow these policies; I better go get tested, too,’ ” Timmer said. She decided to get tested for Covid-19 at a drive-up site.

“I never expected to be positive,” she said, adding that she was “devastated,” because she did not want to miss work.

Not only did she test positive, that was just the beginning of a long battle.

Emerging research suggests that a small portion of people who now live with long Covid may have showed no Covid-19 symptoms at all when they were initially infected – or their symptoms were mild or unusual, similar to what Timmer had.

‘This was my most terrifying time in my life’

Within about two weeks, Timmer had recovered from acute Covid-19 infection. But as she returned to work, she still felt unusual, with problems like overheating, confusion, loss of taste, sound hallucinations and breathlessness.

“I realized the more I tried to walk or return to normal, my symptoms worsened severely, and I would end up in bed with pain and fatigue for weeks,” Timmer said.

“This was my most terrifying time in my life,” she said.

Linda Timmer, 64, with her son in Michigan.

Timmer retired early – before her illness, she had not made plans to retire – and moved to New Mexico in November 2020 to live with her sister while she sought treatment for her ongoing symptoms. In February 2021, she moved to Michigan to live with her son.

Some people with long Covid have said that they noticed their symptoms ease after they got vaccinated against Covid-19. Research also shows that vaccines not only reduce the risk of severe disease and hospitalization, they can lower the odds of long-term Covid-19 symptoms.

Timmer was originally diagnosed with Covid-19 before vaccines became available in the United States. Once they were authorized for her age group, she got vaccinated – and boosted. She felt good after the first vaccine dose, but her long Covid symptoms persisted.

Timmer still has “debilitating” symptoms from long Covid, and she is not alone.

One preprint paper, posted last year to the server MedRxiv, featured an analysis of more than 1,400 medical records in California for people who tested positive for Covid-19. It found that roughly 32% of those reporting long-haul symptoms more than 60 days following a Covid-19 diagnosis had no symptoms at the time of their initial Covid-19 test.

“I’ve seen similar stuff in clinic, as well. Patients coming in with either no symptoms or some very mild symptoms like sore throat, cough, maybe some sneezing, and a few weeks later, debilitating headaches, inability to get up in the morning or just unrelenting fatigue and weakness. And before we knew that long Covid was really a phenomenon, we didn’t know what to do,” said Dr. Ali Khan, who specializes in internal medicine at Oak Street Health in Chicago.

In some people, “we are seeing the coronavirus itself interact with almost every single part of the human body, which is just so atypical for most diseases, particularly most viruses. So we see that in some people – even in people whose initial infections were silent – it can work in the bloodstream to cause you to be more likely to get a blood clot,” he said. “For other people, that coronavirus is attacking the nerves, and it’s causing nerve pain; it’s causing headaches; it’s causing longstanding sciatica that many of my patients are dealing with.”

‘Even people who did not have COVID-19 symptoms … can have post-COVID conditions’

The US Centers for Disease Control and Prevention describes long Covid, or “post-Covid” conditions, as a wide range of new, returning or ongoing health problems four or more weeks after acute Covid-19 infection.

“Even people who did not have COVID-19 symptoms in the days or weeks after they were infected can have post-COVID conditions,” according to the CDC. “These conditions can present as different types and combinations of health problems for different lengths of time.”

The consensus in the medical field is that Covid-19 is an “acute illness” and long Covid is a “subacute chronic illness,” said Dr. Adupa Rao, a pulmonologist with the University of Southern California’s Keck Medicine who sees long Covid patients through Keck Medicine’s COVID Recovery Clinic.

“In the medical world, acute illnesses usually mean a week to two weeks of illness. Subacute means anywhere from two to four weeks and chronic means anything from four to six weeks on that is persistent,” Rao said. “So, the chronic long Covid symptoms are usually people that don’t return to their baseline or close to their baseline after the initial infection – and being able to diagnose long Covid is quite difficult.”

Estimates of long Covid’s incidence range from about 30% to more than half of people who have recovered from acute Covid-19 infection. Women and older adults appear to be more likely to have it than men and younger adults.

Even though the risk of long Covid-19 appears to increase with the severity of acute Covid-19 infection, almost a third of people who had mild symptoms when they were originally diagnosed may still have symptoms months later, according to some estimates.

“We do know that even a mild or relatively asymptomatic acute infection with Covid can eventually cause long Covid,” said Dr. Gerald Harmon, a family medicine specialist and president of the American Medical Association.

“Anywhere from 10% to 30% of patients can experience symptoms of Covid after apparently recovering, even if they weren’t sick in the first place,” he said. “And it’s a wide range of new, returning or ongoing health problems that we typically have put into three different categories.”

The first category, Harmon said, includes people who have direct cell damage that was caused by the coronavirus during the initial infection and takes a long time to recover from. Examples include acute kidney damage, acute lung damage, a big infection of pneumonia in the lung or a blood clot in the brain.

The second category describes people hospitalized with Covid-19 who may have long-term complications from being bed-bound for weeks, such as neurological damage, lung damage or muscle weakness.

Experts are “probably more concerned with” the third category, Harmon said. It includes anyone who recovered from an initial Covid-19 infection that wasn’t severe but then had symptoms.

“And they’re thinking, ‘My goodness, is this a recurrence of the Covid infection? Is it delayed? Is it a new something that’s masquerading as Covid?