In April 2020, I made my yearly predictions, and many of them were about the (then new) coronavirus pandemic.
Two other people on Less Wrong, Zvi and Bucky, decided to test themselves against me by trying to predict the same questions. Zvi saw my answers beforehand; Bucky didn’t. Here’s how we did (except where otherwise stated, all predictions are for 12/31/20):
R in most US states right now is closely clustered around 1. Mutant strains are more contagious, enough to bring the R0 up to 1.5 or so. But having a lot of the population vaccinated will bring it back down again. Also, I’m acting like there’s some complex-yet-illuminating calculation we can do here, but realistically none of this matters. It’s not a coincidence that all US states are closely clustered around 1. It’s the control system again – whenever things look good, we relax restrictions (both legally and in terms of personal behavior) until they look bad again, then backpedal and tighten restrictions. So we oscillate between like 0.8 and 1.2 (I made those numbers up, I don’t know the real ones). If vaccines made R0 go to 0.5 or whatever, we would loosen some restrictions until it was back at 1 again. So unless we overwhelm the control system, R0 will hover around 1 in the summer too, and the only question is how strict our lockdowns will be.
In autumn, if we haven’t already vaccinated everyone there’s a risk things will get worse again because of the seasonal effect. Also, for all we know maybe the virus will have mutated even further and become even more vaccine resistant. Now what?
Are there real randomized controlled trials? Yes – three of them. One from Spain (n = 76) tried randomizing hospital patients to get or not get Vitamin D; the patients in the experimental group did much much much better (25x lower odds of having to go to the ICU!) than the control group. Another from India (n = 40) tested asymptomatic people with mild cases; everyone stayed mild but the patients treated with Vitamin D were three times more likely to clear the infection quickly. The last, from Brazil (n = 240) was a large multicenter RCT that tested whether Vitamin D affected the outcomes of hospital patients. It found no effect whatsoever, not even a hint of a trend.
I could take or leave the Indian trial; nobody is worrying very much about seroconversion in mild cases. The Spanish and Brazilian ones are a pretty jarring contrast. In the Spanish one, the Vitamin D treated patients did 25x better; in the Brazilian one, there was no benefit at all.
I side with Brazil. It’s bigger, more professionally-done, and has fewer minor statistical flaws that really shouldn’t matter this much but make me nervous. Also, in the past I have learned to side with negative RCTs rather than astoundingly massively positive ones when the two conflict. There were some early astoundingly massively positive RCTs for hydroxychloroquine, and then the bigger and more-professionally-done ones that came later showed no effect.