Brain fog, trouble concentrating, and memory loss have become common complaints for many people who have contracted COVID-19. In fact, between 10 and 30 percent of the general population has experienced at least one of these post-infection conditions. Now researchers have not only pinpointed a specific protein that may drive it, but have also shown that vaccination may reduce its impacts, especially for memory loss.

The researchers used a rodent model to better understand how COVID-19 impacts cognitive impairment.

“We looked carefully at their brains during acute infection and then later after recovery to discover what was abnormal in terms of the different immune cells trafficking into the brain and their effects on neural cells,” study author and Schulich School of Medicine & Dentistry professor Dr Robyn Klein said in a statement.

Quite early into the COVID-19 pandemic, it became clear from reports that some people who caught COVID-19 experienced some sort of cognitive impairment. This was a concern for many researchers, who wondered whether the virus invaded the central nervous system.

However, Klein’s previous work had shown that the virus could not be detected in human or rodent brains, which was also confirmed in this latest study. Essentially, something else is going on that does not involve the central nervous system.

What they did find, however, is that COVID-19 infection increased levels of brain Interleukin-1 beta (IL-1β). This is a form of cytokine protein, which are crucial for controlling the growth and function of other immune system cells and blood cells.

Klein and colleagues noticed that the rodent models with increased levels of IL-1β experienced a loss of neurogenesis – the process that creates new neurons in the brain – and showed signs of memory loss.

According to this research, IL-1β may be a potential mechanism that drives COVID-induced cognitive impairment, but could its impact be limited or even prevented by vaccination?

Further rodent models that used vaccinations showed promising results. They found that those that had been vaccinated before contracting COVID-19 had less brain inflammation and lower levels of IL-1β. This meant the vaccinated models had less memory loss and overall cognitive impairment.

Although this is a promising result, there are still limitations to be worked through. For one thing, it is unclear how vaccinations achieve this apparent defense against cognitive impairment. Secondly, the results also need to be translated into human models.

“We know there’s anecdotal evidence that humans who’ve been vaccinated have a much lower risk of developing this long COVID brain fog,” Klein added.

The vaccine used in the study is not one that is available for humans, so future work needs to investigate the connections between vaccination and reduced COVID-19 impacts.

“What we do know is that if you’re vaccinated you have much less inflammation,” said Klein.   

Vaccinations are not able to fully prevent an infection from occurring – this is a common misconception that is harmful to wider trust in their efficacy. Vaccines lower the risks of the impacts from a given infection. So, a vaccine developed to protect from severe pneumonia will not completely prevent you from getting pneumonia, it just helps your body deal with it better. The same is likely true in the context of COVID-19 and cognitive impairment. 

“People need to understand that about vaccines,” Klein said. “They need to know what vaccines can do and what they can’t do.”  

The study is published in Nature Immunology.