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.
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).”