People often make a categorical distinction between randomized clinical trial data and other forms of data. Under this view the only information that can ground medical decision making is a large, multicenter, randomized clinical trial, and other study designs can only prove correlation, not causation. People who hold this view treat clinical trials as determinative of causation. Without a clinical trial you can’t make a causal claim, and once you have one, you no longer need to think that hard about causation.
Black and brown people in northern countries have been disproportionately affected by Covid-19. In the US, Sweden, Canada, and the UK, racialized people have been more likely to contract the disease, more likely to have severe courses, and more likely to die from it. The explanation you usually get for this is that excess mortality is caused by systemic racism or social determinants of health. Under this explanation, there’s nothing that surprising about the high Covid mortality because it’s just another example of discriminatory health care policies.
Imagine that someone offered you a free lottery ticket. You would have a small chance of winning a million dollars, but the ticket doesn’t cost anything. It would be silly to turn down this ticket because you thought your odds of winning were either too small or too unclear; the only reason we care about the odds of winning a game is so that we can determine if the expected value of winning is higher than the expected cost of playing.
In a recent piece about the puzzling ways that Covid-19 has spread across the world the New York Times explores a number of possible theories about why Covid-19 has affected some countries more grievously than others, including “demographics, culture, environment, and the speed of government responses.” I think Vitamin D status should probably be included in this conversation. A tale of two countries Canada and Australia have had pretty similar Covid-19 timelines.