New global research is being driven by the mystery of how SARS-CoV-2 may cause brain fog or other neurological symptoms in some people.

In the first two years of the pandemic, approximately 79 million US nationals became infected with COVID-19. While the majority of people survived, many are dealing with long-term symptoms, also known as long Covid, that affect the brain and other body systems.

The NIH's Avindra Nath and Yale's Serena Spudich wrote in a January Science perspective that there is an "urgent need" to research the disorders and develop therapies.

It is worth mentioning that many germs are often prevented from entering the brain by the blood-brain barrier, but certain pathogens are able to breach it.

It's unclear whether SARS-CoV-2 can directly cross that barrier, though recent research suggests it can.

Autopsies have also revealed that SARS-CoV-2 infections in cells near the brain can inflame brain-barrier cells and that this inflammation can be relayed into neurons and glial cells in the brain.

A study of 785 people - aged 51 to 81 - published this week in Nature found that COVID can shrink the size of the brain, with some people showing as much as a decade of normal aging months after infection.

However, there is some concern that it may hasten or trigger the onset of Alzheimer's or Parkinson's disease.

Meanwhile, the NIH and others are investigating whether the changes are reversible, whether they affect younger as well as older people, whether changes in the brain are directly related to the brain fog people experience, and what the best therapeutic options will be.

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