R.F.Kennedy jr. - How 100% Effective was Calculated From the First Covid Vaccine Subjects

R.F.Kennedy jr. - First Covid Vaccine Trials - 44,000 Subjects - 22,000 Vaccinated - 22,000 Placebo.
Placebo group would really be gone if they got 100% of the population to take the shot.
But there are many non-vaxed people that can be a baseline norm.

Also, %100 effective was a number that was derived from factual numbers of 2 deaths in placebo, and 1 death in vaccinated. That is %100 more deaths in placebo group.
What if 3 deaths were in placebo group, is that %200 effective?
Also, how did they derive the lower efficacy percentages as time went on. Take a guess.?