Vitamin D deficiency is about the right fraction of the population, 29-41% depending where you set the threshold, which approximately matches the household secondary attack rate and the infection rate at superspreading events.
It varies over time with random variation in diet and indoor/outdoor activity patterns.
I think there’s a reasonably high chance that, if any town had handed out 5kIU vitamin D supplements to everyone, that town would have had almost no cases.
This is an interesting hypothesis, but I find it implausible that there is large temporal variation in vitamin D levels. Seasonal variation which might be even the biggest factor affects everybody the same, and it just does not seem to match my experience that the majority of the population changes their diet in such random ways that they could become Vitamin d deficient by chance. Same with indoor/outdoor activities, most people’s life is not that variable that they are spending each day outside one month, but not the next. Besides, Vitamin D deficiency is correlated very strongly with various commodities, which definitely do not randomly fluctuate.
I would also bet that the secondary household attack rate is similar across different age groups (except children) while it is known that Vitamin D deficiency is much likelier in older people.
I think vitamin D deficiency might be the hidden factor that determines vulnerability. Reasons for thinking this:
Vitamin D is an immune modulator, so there’s a clear mechanism.
Vitamin D deficiency is about the right fraction of the population, 29-41% depending where you set the threshold, which approximately matches the household secondary attack rate and the infection rate at superspreading events.
It varies over time with random variation in diet and indoor/outdoor activity patterns.
It correlates with season, latitude, race and BMI.
I think there’s a reasonably high chance that, if any town had handed out 5kIU vitamin D supplements to everyone, that town would have had almost no cases.
This is an interesting hypothesis, but I find it implausible that there is large temporal variation in vitamin D levels. Seasonal variation which might be even the biggest factor affects everybody the same, and it just does not seem to match my experience that the majority of the population changes their diet in such random ways that they could become Vitamin d deficient by chance. Same with indoor/outdoor activities, most people’s life is not that variable that they are spending each day outside one month, but not the next. Besides, Vitamin D deficiency is correlated very strongly with various commodities, which definitely do not randomly fluctuate.
I would also bet that the secondary household attack rate is similar across different age groups (except children) while it is known that Vitamin D deficiency is much likelier in older people.
Supporting your point, the ACX post on COVID and Vitamin D cites this study finding that Vitamin D levels are relatively stable.
Relevant from the abstract: “The 25(OH)D levels were correlated between visits 2 and 3 (3 y interval) among whites (r = 0.73) and blacks (r = 0.66).”