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They were divided into two: one half were injected with the original vaccine and the other half were injected with a placebo (empty medicine). Then the participants went about their activities as usual and were monitored whether anyone was exposed to Covid-19.
The result was 170 participants were infected with Covid-19. From here, they were then split again. If out of those170 people affected by Covid-19 there were 85 injected with the vaccine and 85 injected with a placebo, the efficacy is zero percent.
If the 170 infected were those who received the empty medicine, it means that the vaccine's efficacy reached 100 percent.
In this trial, out of 170 people, only eight were infected with Covid-19 after receiving the vaccine and the rest received a placebo. So, the efficacy is 95 percent.
Unfortunately, the level of efficacy is not the only benchmark.
Clinical trials of all vaccines of course use the same methods as described above.
But the problem is what the situation was like when the clinical trials were held?
"One of our biggest considerations when looking at these numbers is when the clinical trial was conducted," said microbiologist Deborah Fuller of The University of Washington.
Pfizer BioNTech and Moderna conducted their clinical trials in the summer of 2020 (approximately August to November 2020) when COVID-19 cases in the US have not yet reached its peak.
