Mild Covid-19 Can Cause Brain Damage

A Summary of The Evidence

As the delta variant of COVID-19 spreads and infects a growing number of fully vaccinated people, many take comfort in the fact that a breakthrough infection is likely to be mild. However, a mild COVID-19 infection is still quite risky. A growing body of evidence suggests that a mild case of COVID-19 can cause long-term brain damage, including:

Long-term cognitive impairment
Memory problems
Damage to senses of smell and taste
Increased risk of dementia and Alzheimer's disease

For many of us, this evidence is hard to accept and does not match our experience. Most of us know someone who has recovered from a mild COVID-19 infection and reports no lingering symptoms. But even in these cases, damage may have occured -- the neurological impact of this virus is often mild enough to be imperceptible to the individual, at least initially.¹

Still, though these effects may be subtle, they are measurable and consequential -- on average, people who've had mild COVID-19 perform worse on cognitive tests and show patterns of brain tissue loss that appear "strikingly similar to those associated with Alzheimer’s disease or other forms of dementia,"² raising concerns that the "long-term consequences of COVID-19 may include these disorders."

Update: In addition to the studies covered below, the July 2021 Alzheimer’s Association International Conference featured an additional batch of new studies supporting a link between mild COVID-19 and cognitive decline.

Study #1

Brain imaging before and after COVID-19 in UK Biobank

Sample Population: 394 COVID-19 survivors (most had mild cases) and 379 healthy controls
Method: Brain scans conducted pre- and post-infection
Finding: COVID-19, including mild cases, accelerates tissue deterioration in several regions of the brain
Media Coverage:
- Alarming COVID study indicates long-term loss of gray matter and other brain tissue

Study #2

Cognitive deficits in people who have recovered from COVID-19 relative to controls

Sample Population: 84,285 Britons
Method: Intelligence test
Finding: COVID-19 survivors--included those who'd had mild cases--performed worse on intelligence tests compared to healthy controls
Media Coverage:
- Recovered COVID-19 patients exhibit cognitive deficits

Study #3

Cognitive decline among individuals with history of mild symptomatic SARS-CoV-2 infection

Sample Population: 93 Villagers in Atahualpa, Peru; 52 survivors of mild COVID-19 and 41 healthy controls
Method: Cognitive assessments and brain scans
Finding: Survivors of mild COVID-19 were 18 times more likely to exhibit cognitive decline

Study #4

Frequent neurocognitive deficits after recovery from mild COVID-19

Sample Population: 18 adults, mostly young adults, who had recovered from mild-to-moderate COVID-19
Method: Cognitive assessments
Finding: 78% of COVID-19 patients performed poorly on cognitive tests, compared to healthy controls. "Our results demonstrate that sustained sub-clinical cognitive impairments might be a common complication after recovery from COVID-19 in young adults."

Study #5

The landscape of cognitive function in recovered COVID-19 patients

Sample Population: 29 recovered COVID-19 patients at Zhejiang University School of Medicine
Method: Cognitive assessments
Finding: "Our findings indicated that cognitive impairments exist even in patients recovered from COVID-19."