Blood clots
Studies have shown the overcharged inflammatory response to COVID-19 can cause blood clots. This sometimes overwhelming clotting was an early hallmark of COVID-19 infection, and when clots restrict blood flow in the brain, lungs, kidneys, or limbs, they can cause long-term damage. Some can be deadly. Researchers in Sweden found patients were at risk of deep vein thrombosis – a blood clot usually in the leg – up to 3 months after infection and at higher risk of a blood clot in the lung, called pulmonary embolism, for as long as 3 months.
Viral reservoirs
The virus itself may also linger in a patient’s body, causing continued symptoms and, potentially, new flare-ups. Zoe Swank, PhD, of Harvard Medical School, Boston, and colleagues reported in a preprint study that they found pieces of the SARS-CoV-2 virus in the blood of most patients with long COVID symptoms they tested – some as long as a year after infection. The study has not yet been peer reviewed.
Another team found evidence of the virus in stool up to 7 months later, which suggests the virus hides out in the gut. Other early studies have found bits of viral RNA in the appendix, breast tissue, heart, eyes, and brain.
Diabetes
Diabetes is a risk factor for getting severe COVID-19, and multiple studies have shown people can get diabetes both while battling infection and afterward. One study of veterans, published in The Lancet Diabetes and Endocrinology, found COVID-19 survivors were about 40% more likely to get diabetes over the next year.
There are a few ways this might happen. Insulin-producing cells in the pancreas have SARS-CoV-2 receptors – a type of molecular doorway the coronavirus can attach to. Damage to these cells could make the body less able to produce insulin, which in turn can lead to diabetes. The virus could also disrupt the balance in the body or cause inflammation that leads to insulin resistance, which can develop into diabetes, Ziad Al-Aly, MD, of the Veterans Affairs St. Louis Health Care System, and colleagues wrote.
Nervous system issues
People who get COVID-19 are also more vulnerable to postural orthostatic tachycardia syndrome (POTS). This affects what’s known as the autonomic nervous system, which regulates blood circulation, and includes those things that happen in your body without your having to think about them, like breathing, heartbeat, and digestion. POTS can cause common long COVID neurologic symptoms, including headaches, fatigue, brain fog, insomnia, and problems thinking and concentrating. “This was a known condition prior to COVID, but it was incredibly rare,” said Dr. Viswanathan. “After COVID, I’ve seen it with increasing frequency.”
Long-term outlook
Lasting issues after COVID-19 are much more likely after a moderate or severe infection. Still, plenty of people are battling them even after a mild illness. “As for why, that’s the billion-dollar question,” said Dr. Horwitz. “It’s well known that viral infections can cause long-term dysregulation. Why that is, we really just don’t know.”
Whether it’s virus hiding out in the body, long-term organ damage, or an autoimmune reaction likely differs from person to person. “I’m believing, increasingly, that it’s a combination of all of these, just based on how different patients are responding to different medications,” said Dr. Viswanathan. “One patient will respond to something beautifully, and another patient won’t at all.”
But it’s clear a significant number of people are facing long-term health struggles because of COVID-19, which has infected at least 580 million people globally and 92 million – likely many more – in the United States, according to Johns Hopkins University.
Even a small increased risk of conditions like heart disease or diabetes translates to a huge number of people, Dr. Horwitz said. “If even 1% of people getting COVID have long-term symptoms, that’s a major public health crisis, because that’s 1% of pretty much everybody in the country.”
A version of this article first appeared on WebMD.com.