EDIT: I forgot (or didn’t know) that loss of sense of smell was less likely with Omicron, which Steven Byrnes pointed out. Seems like 12-20% (probably mostly vaccinated?) of Omicron infections vs 7-68% for previous variants (section 3.5, and I’m not sure to what extent vaccination status was considered here). I’ve also read that Delta was less likely to cause loss of sense of smell than earlier variants, too. If the probability of loss of sense of smell scales proportionally with other brain issues, then I’d guess Omicron is less severe than previous variants (assuming 2 doses of mRNA vaccines against Delta, and 3 against Omicron, with the last one recently). Maybe by a factor of ~2x, which is somewhat but not extremely reassuring.
Also, it’s not clear that long COVID is less bad or less likely with Omicron than Delta (for a fully vaccinated person). IIRC, vaccines are less effective at reducing symptoms even conditional on catching COVID, and the supposed mildness of Omicron might be explained by which part of the respiratory system it attacks, but that might not have much bearing on how it affects the nervous system and brain in particular (if it does). Brain fog and chronic fatigue seem more like brain issues than respiratory issues, although maybe poor breathing could cause both?
There are studies for and against COVID infecting the brain (I haven’t taken the time to evaluate them), and in particular olfactory regions, which could explain long term loss of smell. If it does have a route to the brain, that’s very worrying and would likely rule out a purely psychosomatic explanation (although both could be involved), although I agree that the severity of some cases, the specificity of some symptoms, and long COVID progression (IIRC, it can have a fairly delayed onset) make a purely psychosomatic explanation unlikely already.
EDIT: Here are a few studies, but I wouldn’t consider this a particularly representative sample, and again, I haven’t looked through them in much detail.
I thought omicron didn’t cause as much loss of sense of smell as previous strains? I was thinking of that (very tentatively) as a good sign, like “omicron is less of a destroyer of nerve cells”, and I think of nerve cells as being unusually difficult to heal, cf. polio. (Omicron does cause brain fog, which is bad but not necessarily associated with the killing of nerve cells, or at least that’s my vague impression / guess.) Low confidence on all this.
EDIT: I forgot (or didn’t know) that loss of sense of smell was less likely with Omicron, which Steven Byrnes pointed out. Seems like 12-20% (probably mostly vaccinated?) of Omicron infections vs 7-68% for previous variants (section 3.5, and I’m not sure to what extent vaccination status was considered here). I’ve also read that Delta was less likely to cause loss of sense of smell than earlier variants, too. If the probability of loss of sense of smell scales proportionally with other brain issues, then I’d guess Omicron is less severe than previous variants (assuming 2 doses of mRNA vaccines against Delta, and 3 against Omicron, with the last one recently). Maybe by a factor of ~2x, which is somewhat but not extremely reassuring.
Also, it’s not clear that long COVID is less bad or less likely with Omicron than Delta (for a fully vaccinated person). IIRC, vaccines are less effective at reducing symptoms even conditional on catching COVID, and the supposed mildness of Omicron might be explained by which part of the respiratory system it attacks, but that might not have much bearing on how it affects the nervous system and brain in particular (if it does). Brain fog and chronic fatigue seem more like brain issues than respiratory issues, although maybe poor breathing could cause both?
There are studies for and against COVID infecting the brain (I haven’t taken the time to evaluate them), and in particular olfactory regions, which could explain long term loss of smell. If it does have a route to the brain, that’s very worrying and would likely rule out a purely psychosomatic explanation (although both could be involved), although I agree that the severity of some cases, the specificity of some symptoms, and long COVID progression (IIRC, it can have a fairly delayed onset) make a purely psychosomatic explanation unlikely already.
EDIT: Here are a few studies, but I wouldn’t consider this a particularly representative sample, and again, I haven’t looked through them in much detail.
For brain route:
Song et al., January 2021, Neuroinvasion of SARS-CoV-2 in human and mouse brain
Douaud et al., August 2021, Brain imaging before and after COVID-19 in UK Biobank (not yet peer-reviewed)
Against brain route:
Khan et al., November, 2021, Visualizing in deceased COVID-19 patients how SARS-CoV-2 attacks the respiratory and olfactory mucosae but spares the olfactory bulb
I thought omicron didn’t cause as much loss of sense of smell as previous strains? I was thinking of that (very tentatively) as a good sign, like “omicron is less of a destroyer of nerve cells”, and I think of nerve cells as being unusually difficult to heal, cf. polio. (Omicron does cause brain fog, which is bad but not necessarily associated with the killing of nerve cells, or at least that’s my vague impression / guess.) Low confidence on all this.
Hmm, ya, that seems right. From a quick Google search: https://www.businessinsider.com/loss-of-taste-smell-not-common-covid-symptoms-2022-1.
Maybe Omicron just doesn’t get as deep in the body generally, too, then. That would be a good sign, too.