Brain fog from Long COVID leads to 6 point IQ loss

While many people with Long COVID have reported neurological symptoms like brain fog, there has, until recently, been no objective measurement of how severely people really are affected. That was until a new study from Imperial College London, recently published in the New England Journal of Medicine, found that people experiencing Long COVID saw cognitive deficits equivalent to a 6 point loss in IQ. The lead author of the study is Adam Hampshire…

Adam - We built on the back of one of the largest epidemiological studies that was run in the UK during the pandemic. It was called React, which is the real time assessment of community transmission. And that was a project where they sampled somewhere in the order of about three and a half million people randomly within the general population to see at different points in the pandemic whether they had been infected with the virus and whether they had covid or not. So we kind of got this background on people's history of covid if you like. And what we did is we recontacted 800,000 of them and asked them to take part in an online cognitive assessment on a platform that's called cognitron that can measure different aspects of cognitive and memory ability through people's laptops, their smartphones. And out of those people we contacted, there's about 140,000, did at least one of our tests and about 112,000 completed the entire assessment.

Chris - How big are the differences that you are detecting? So if I took an IQ test for example, and I was affected in the way that some of the people you registered in the study were affected, how many IQ points down would I effectively be if I were affected in that way?

Adam - If we treat the global score from this assessment like an IQ test, then the group with the largest cognitive deficit is on average people who were in intensive care. And so they showed a difference of around about minus nine IQ points. People who have ongoing persistent symptoms, that is the ones who may have long covid, they perform at about minus six IQ points and that's enough that it could have affected your daily function. You are very likely to be aware and notice that change. The larger number of people of course sit in the short term symptom group and they show a difference on average of about minus three IQ points and that's very small. But we are powered, we are able to detect that because we measured so many people.

Chris - Were there any things that leapt out in people who got SARS CoV 2 infection where certain elements of cognition were consistently impacted or is it just an across the board reduction for at least a period of time in everybody?

Adam - In terms of aspects of cognitive ability, we saw the strongest relationships with having had Covid 19 in memory function reasoning and what we call executive function things like planning. That's the case. If we were looking at, for example, people who had longer term sort of ongoing persistent symptoms. So what some people would refer to as long covid

Chris - And critically, when a person says they get better, because we know that a proportion of people have symptoms for a certain period of time and then they get better. When they get better, does their cognition go back to normal? Do you think?

Adam - We have to be very careful here in terms of the inferences that we draw. What we're looking at are essentially associations. We are not looking at change because we have only measured one time point. Nonetheless, the pattern of results that we see shows that people who have ongoing persistent symptoms perform worse than people who have shorter duration symptoms. Whilst that's the case, even people who had short duration symptoms on average showed slightly worse cognitive performance compared to people who had not had covid at all. The really interesting group of people who had ongoing persistent symptoms. But by the time we cognitively tested them, those had resolved. That set of participants performed at the same level as people who had only short-term persistent symptoms. That is only a small cognitive deficit was still evident.

Chris - Well that's slightly encouraging, isn't it, because it notwithstanding the fact that this is an association would argue that there should be an improvement in someone when their symptoms overall subside.

Adam - Exactly. I think on the face of it, our study has some results that were quite negative and not really what we hoped to see. For example, we don’t see any association between shorter duration covid and cognition. And that's somewhat worrisome. It's not what we were looking for or we didn't predict that. On the other hand, it does appear to be the case that people who have long-term persistent symptoms, when those symptoms eventually subside, they may well have some degree of recovery in their cognitive and memory abilities. Another really quite promising result that we had was that actually several of the results in the study converged towards indicating that this association between covid and cognition has reduced throughout the pandemic. So the association was larger for the original virus and for the alpha variant, but by the time we get to Omicron it seems to have been diminished.

Chris - To what do you attribute that? Do you think that's because by that time it's hitting people who've been either infected before and recovered or vaccinated before and are therefore subject to a less severe infection?

Adam - Well, our model takes all of these things into account, but they're quite hard to disentangle because they correlate across time. So of course if you think through the course of the pandemic, different virus variants were dominant. Right? And then in addition to that, partway through they started to roll out vaccinations and approaches to treatments probably improve somewhat as well. Within the model, it would appear to be the case that if a person was vaccinated at least twice prior to their infection, they have a small cognitive advantage relative to people who had not yet been vaccinated. So I think that's one aspect that's probably coming into play and it's very likely that later variants had a lesser impact on cognition as well. So these things aren't mutually exclusive.