Midwest, really all the people in states north of 30 degrees parallel, have a hard time producing enough Vitamin D through the sunlight. Reports are that the solar rays are simply much weaker north of 30 degrees and not strong enough to trigger adequate Vitamin D production in the human body. Reminds me of why we put iodine in salt.
I welcome correction, and concede this does not explain and even contradicts the rise in cases in the southern states in the Summer (when all the ‘experts’ thought it would help slow the spread) but seems to me come the fall the midwest could indeed have another wave of ailments - if not covid (the Vit D connection is not well established) then the usual stuff made worse by the unknowable side effects of long term lockdowns.
People with lighter complexions produce more vitamin D.