How is the effectiveness of the vaccine measured? By comparing the number of people (vaccinated vs. placebo) who get sick in a period of time. If they have the gender, age, weight, general condition of the volunteers, and location . . . it seems they have no control on other factors (mask carrying, social contacts and behavior, . . .) at least, it is not reported in the data released. On the other hand, finding antigens in the blood is not a sign that you cannot get sick. So, 90% effectiveness???