pfizer trial showed first dose by itself was extremely effective. check out the chart here: https://www.businessinsider.com/how-well-pfizer-shot-works-a...

Much of the data comparing efficacy of 1 vs 2 doses doesn't wait until 10-days after the first dose, which defeats the point. That being said 2 doses is more effective, just not by as much as you'd might think.

edit: replaced the above link because it was pay-walled