One thing seems to be sure, and that is that the hallmark of long-term COVID survival may be a form of cognitive decline. That doesn’t mean impending dementia, but a loss of sharpness in what is now referred to as the “fog” of COVID.
According to a Current Population Survey of Americans, there were less than 15 million people in the United States aged 18 to 64 who had some form of handicap at the beginning of the year 2020. By September 2023, that number had risen to almost 16.5 million. And nearly two-thirds of those adding to the total had previously unreported restrictions on their cognitive abilities.
A prime factor in the increase in people with a cognitive disability appears to be COVID-19, and while the vast majority of people who contract it make full recoveries, some people who contract the virus continue to experience symptoms months or even years after the initial infection. The puzzle for scientists is what is causing this brain fog of cognitive impairment and what might be done to remediate it.
Post-acute sequelae of SARS-CoV-2 (i.e., symptoms continuing for at least 4 weeks after infection), also known as protracted COVID, include fatigue and cognitive impairment, along with other enduring neuropsychiatric (e.g., depression) and physical (e.g., dyspnea) manifestations. Working memory fluctuations would appear to be most distressing and may account for increased applications for disability. Note: Disability requires the three factors of maintaining pace, persistence, and concentration (aka PPC), and the memory impairment shown in COVID patients would increase the likelihood of receiving benefits.
For one thing, rigorous data on the incidence of the illness appears to be lacking and we do not know how many people have COVID or how many are suffering its long-lasting effects. As of December 2021, the number of confirmed cases of coronavirus illness around the world had risen to almost 275 million. However, numerous models suggest that the true number of cases is three to twenty-four times higher than the number of confirmed cases.
Researchers have proposed numerous reasons for the changes in cognition and general well-being, including viral persistence, chronic inflammation, hypercoagulability, and autonomic dysfunction. One new hypothesis is being offered for a reduction in a vital neurotransmitter, serotonin. However, most of the work is being evaluated with mouse models.
Certain structures or pathways can lead to changes in memory. One is a drop in serotonin, which can stop the vagus nerve from working properly, which in turn affects how the hippocampus responds and stores memories. The hippocampus is the brain structure most involved in memory consolidation, so anything that interferes with its functioning could result in a change in memory formation and retrieval.
For now, all we know is that there are multiple factors involved in brain fog and fatigue after being infected with the virus for COVID. There are also many physical organ systems that are also affected, so this is a virus, seemingly, unlike others scientists have encountered in the past.