That is partially correct, and thanks for pointing that out in my comment. The efficacy is measured in preventing COVID symptoms. Some of these trials are measuring all symptoms and others more moderate/severe symptoms.
In the Pfizer trial, there were 41,135 participants who received both doses. From this cohort, preliminary results showed 170 COVID cases were recorded, of which 162 were from the placebo group and 8 from the vaccine group. Of these 170 cases, there were 10 severe cases: 9 from the placebo, and 1 from the vaccine group.
This may (or not, we’ll find out soon) be sufficient enough data to warrant an EUA in this landscape. But, a 0.4% positivity rate (and 0.02% severe case rate) among all trial participants is quite low compared to the case rates in the general US population. This is because we only have preliminary results. Full trial results will be made available when the usual timeframe for phase 3 trials have passed—in a couple years.