“We’ve seen hundreds and hundreds of people with many different lingering post-COVID-19 symptoms, and among the most common are problems with memory and thinking,” says clinic director and physical medicine and rehabilitation physician, Janna Friedly, MD. It’s estimated than anywhere from one-fourth to one-third of people with COVID-19 have long-lasting symptoms — and not just people who have been hospitalized. Approximately 1 in 3 people who had mild to moderate COVID-19 symptoms reported lingering symptoms seven to nine months later, according to a study published in July 2021 in the Annals of Internal Medicine. “People often report that they’re having difficulty finding the right words and remembering things that are very common to them, such as the names of their friends, the locations of familiar things, and driving directions,” says Dr. Friedly. A study published July 15, 2021 in The Lancet looked at COVID-19 long-haulers and found that six months after infection, the most common symptoms included fatigue, malaise after exertion, and cognitive problems or “brain fog.” “We’re also seeing a lot of people with significant anxiety and depression, sleep disruption, fatigue, and a variety of other neurological symptoms as well,” she says. These symptoms are found in both people who had only very mild COVID-19 and in those who had much more severe infections, says Friedly. In many cases, these symptoms improve with time and rehabilitation, but experts are concerned about lasting effects on COVID-19 on the brain, says Ronald C. Petersen, MD, PhD, director of Mayo Clinic Alzheimer’s Disease Center. “The question is, will people develop cognitive impairment of a more persistent nature down the road after the acute infection is over,” he says. Researchers have found that some genes responsible for increasing the risk of severe COVID-19 are also linked to a higher risk for Alzheimer’s disease (AD), says Friedly. Brain scans taken before and after COVID-19 also indicate that COVID-19 may cause changes similar to those observed in people with AD, according to a preprint study posted on medRxiv on June 20, 2021.

COVID-19 Impacts More Than Just the Respiratory System

It appears that there are different modalities of COVID-19, and we know it can affect memory and thinking during the acute infection phase, says Dr. Petersen. “That’s because of the large inflammatory response that can affect the respiratory system, the brain, and other parts the body,” he says. Researchers are still learning about what causes different long-haul symptoms, which includes exploring different theories about why cognitive issues such as brain fog and memory loss can persist, says Friedly. “It could be either a direct effect of the virus itself, but what’s probably more likely is that it’s related to some of the inflammatory reaction to the virus that been observed throughout the body,” says Friedly. That response can cause neuroinflammation and vascular changes that might impact brain function, she says.

It’s still too early to know what factors may put a person at higher risk for having short-term or more long-lasting cognitive issues post-COVID, says Friedly. “There’s a lot of research going on right now that’s trying to answer those specific questions,” she adds. Some research suggests that there may be some genetic component to it, says Friedly. “It may be that people who have a particular gene that is common to having a higher risk for developing Alzheimer’s disease may also be associated with the risk for developing cognitive dysfunction post-COVID-19; we definitely need to do additional research to confirm that. There also may be other factors that we haven’t identified yet,” she says. Petersen agrees, saying, “It’s too early to know all factors that may put someone at risk for cognitive issues or neurologic injury related to COVID-19. In general, an older person or a person with other medical issues might be more susceptible, but a lot of that is speculation at this time,” he says.

Previous Viral Illnesses Have Been Linked to Cognitive Changes

Some people who had the flu during the 1918 influenza epidemic developed a complication in the nervous system after they recovered, says Petersen. “It was called von Economo’s encephalitis or encephalitis lethargica, and some of those people developed Parkinson’s disease-like symptoms,” he says. Some of those symptoms occurred decades after the original infection, he adds. “There are other viral illnesses of the brain where the virus actually gets into the brain, such as HIV and certain herpes viruses,” he says.

Registries, Long-Term Studies Aim to Answer Questions About COVID-19 and Alzheimer’s Risk

“It’s still early in the pandemic and so we don’t have long-term data yet on what the trajectory will be for people who have cognitive dysfunction related to COVID-19,” says Friedly. According to Petersen, there currently studies underway for people who have been infected with COVID-19 that include different types of assessments, including baseline examinations, PET scans, MRI scans, cerebrospinal fluid or lumbar punctures, and blood work, says Petersen. “These people can be followed and tested periodically to look for signs of changes in the brain or brain function,” he says.

Many People With COVID-19 Cognitive Symptoms Have Recovered

“The good news is we have many patients who have gotten much better; their cognitive issues have improved with some of our rehabilitation strategies and with time,” says Friedly. That suggests that COVID-19’s impact on the brain is either temporary or reversible to some extent, she says.

A Vaccine Is the Best Defense Against Cognitive Changes Due to COVID-19

While we’re still figuring out who is at risk for the post-COVID-19 symptoms, we do know that the single biggest risk factor for experiencing them is getting infected with COVID-19 in the first place, says Friedly. “The more that you can do to protect yourself against getting the virus, the lower your risk of any related long-term cognitive dysfunction,” she says. “In terms of comparing the risks, COVID-19 poses a far greater risk than getting the vaccine; I highly encourage everyone to get vaccinated,” says Friedly.