Consistent with these findings, our study confirmed rapid S1 protein entry into multiple brain regions and demonstrated that S1 exposure leads to impairments in episodic memory, spatial learning, and increased anxiety, suggesting that persistent spike protein contributes to long-term cognitive decline.

Earlier in the article they state that around 28% of surviving patients experience "brain fog" for months or years. That is people that have it bad enough to search for medical care. This many people having lower memory and learning abilities and living with heightened anxiety would explain a lot of things.