Very good morning doctors. when it says that you have 52 percent protection after the first phizer shot, what does that mean? 52 percent of what?

Suppose there are 2 similar groups of people, and the only difference is that one group got the vaccine but the other did not. After a time of observation (a number of weeks, months, etc.) we count the people in each group who caught the disease. 52% protection means the number of vaccinated people who caught the disease was 48% of the number of unvaccinated people who caught it. (48 + 52 = 100%)