Here is the story from the Associated Press: Scientists mystified, wary, as Africa avoids COVID disaster.
One suggestion in the article is that sunlight might fight the spread of the disease. This is because ultraviolet light can kill (or neutralize) viruses in the air, perhaps decreasing transmission when persons are outdoors.
But sunlight has another benefit. UV light on skin produces vitamin D. A meta-analysis of 142 studies showed that optimal levels of vitamin D in the blood reduces many different risks from Covid-19. Persons with good levels of vitamin D in the blood have reduced risk related to Covid-19, including: risk of infection; of having a severe case; of needing hospitalization, ICU care, and/or mechanical ventilation; as well as the risk of dying from Covid-19. Then vid also seems to improve overall outcome for Covid-19 cases. See the Covid-19 vitamin D studies here.
If you do not receive much sunlight on skin (to produce vitamin D naturally), consider taking a vitamin D supplement. the Vitamin D Letter signed by over 200 scientists and doctors recommends 10,000 IU of vitamin D per day for 2 to 3 weeks, followed by 4,000 IU per day of vitamin D.
What other vitamins might be helpful? This study found that vitamin K and vitamin D are each independently associated with a reduction in Covid-19 disease severity. Vitamin K can be obtained from a supplement, preferably one with Vitamin K1 and the Mk-4 and Mk-7 forms of vitamin K2. Then a deficiency in either or both vitamin K and vitamin D were associated with increased risk of severe Covid-19 disease. The study also suggested that having good levels of both vitamins might be synergistic, having a greater benefit that then sum of each.
“Participants who were vitamin D defcient (780 ng/mL) and experienced the most severe COVID-19 outcomes.” [1]
1. Desai, Ankita P., et al. “Vitamin K & D Deficiencies Are Independently Associated With COVID-19 Disease Severity.” Open Forum Infectious Diseases. Vol. 8. No. 10. US: Oxford University Press, 2021.
Ronald L. Conte Jr.
Covid.us.org
an author, not a doctor
Covid.us.org 
It seems that most people think that the seasonality of COVID-19 and influenza, in areas more than about 30 degrees from the equator, is due to people spending more time indoors when meeting others (outside their family group) in winter, with closed windows. I think this is a factor, but only a minor one compared to the seasonal changes in 25-hydroxyvitamin D levels.
Please see my article on this https://nutritionmatters.substack.com/p/covid-19-seasonality-is-primarily and the research articles I cite at: “What every MD, immunologist, virologist and epidemiologist should know about vitamin D and the immune system” https://vitamindstopscovid.info/05-mds/ .
I have not had time to research the best form of vitamin K2 to take, or in what quantities, given that there is some in vegetables and fruit. Even vitamin A is quite complex – I am not sure what form is best, or to what extent supplementation is necessary depending on diet. The 1,25-dihydroxyvitamin D – vitamin D receptor complex binds to the retinoid X receptor in the nucleus before the complex of these can alter gene transcription – and this is derived from Vitamin A.
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