Almost a year into the global pandemic, doctors and scientists are still coming to terms with a concerning phenomenon.

It’s not a mutant strain or a side effect of the vaccine, but the aftermath of the disease that is crippling those diagnosed.

Weeks after they were expected to recover from the virus, many are suffering from complications caused by COVID-19, which is affecting their entire body, from severe fatigue to memory lapses to digestive problems, erratic heart rates, fluctuating blood pressure and hair loss.

Many of those who are suffering from the after-effects had minimal symptoms when originally diagnosed and doctors assumed recovery would take about two weeks.

And then there are the “long haulers”, suffering a condition experts have deemed “post-acute COVID” or “chronic COVID”.

“Usually, the patients with bad disease are most likely to have persistent symptoms, but COVID doesn’t work like that,” Oxford University professor of primary care, Trisha Greenhalgh, told The Wall Street Journal.

The lead author of an August BMJ study, Professor Greenhalgh was one of the first to define chronic COVID-19 patients as those whose symptoms span multiple organ systems and last over 12 weeks.

“The disease itself is not that bad” for them, she explained, yet cognitive issues and heart problems sometimes persist for months.

While other outbreaks such as the Spanish flu and ebola have had long-term symptoms, what makes COVID-19 different is that it doesn’t just impact the lungs, but the heart, kidneys, nervous and digestive systems.

“I haven’t really seen any other illness that affects so many different organ systems in as many different ways as COVID does,” medical director for Mount Sinai Health System’s Centre for Post-COVID Care in New York, Zijian Chen, told the WSJ.

“We thought it was a virus that, once it does what it does, you recover and you go back to normal.”

Turns out, that isn’t the case, he added it “is really scary”.

One explanation for what’s causing the virus’ second act is that inflammation continues to affect organs or the nervous system even after it’s gone, researchers said.

“Even those who had no symptoms and were young and fit … even in those patients we saw abnormalities,” director of the University Hospital Frankfurt’s Institute for Experimental and Translational Cardiovascular Imaging, Eike Nagel, said.

“You don’t realise how lucky you are with your health until you don’t have it,” 43-year-old lawyer, Elizabeth Moore, told the publication. Since contracting COVID-19 last March, she has struggled with memory problems and gastrointestinal issues, losing almost 14kg.

At the end of April, “I thought I beat this thing. I was ecstatic,” she said. But after testing positive for coronavirus antibodies in May, Ms Moore said her health took a sharp turn for the worse, leading to tachycardia (racing heartbeat) and fluctuations in her blood pressure.

While those symptoms have improved, the mother-of-three is still dealing with the gastrointestinal problems and a recent test found her stomach lining is inflamed.

“I feel like there has to be some sort of next step,” she told the WSJ. “Because I’m not ready to accept this as my new reality.”

This article originally appeared on Over60.