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The Health Ministry explained on Monday that a 95% effectiveness of a vaccine against the new coronavirus means that, compared to an unvaccinated person, an immunized person has a 20 times lower risk of developing symptomatic COVID-19.
"95% efficacy does not mean, as it may be easy to believe, that in 5% of cases the vaccine fails and is useless. In fact, '95% efficacy' means that, compared to an unvaccinated person, a vaccinated person has a 20 times lower risk of developing symptomatic COVID-19. How is this estimate of efficacy achieved? Through clinical trials," the Health Ministry said on its Facebook page.
The ministry indicated in this regard the clinical trial that was the basis for the approval of the Pfizer BioNTech vaccine and which followed 43,448 people, divided into two groups: one included people who were given the vaccine and the other people who were given placebo (a saline solution).
"In both groups, the injections were given 21 days apart. One of the main objectives of the trial was to determine the effectiveness of the vaccine against the development of symptomatic COVID-19 at least 7 days after the second dose. Of the 21,720 people who received the vaccine, only eight developed specific symptoms of COVID-19 and were confirmed by RT-PCR testing, and from the other 21,728 people who received placebo (saline), 162 developed specific symptoms of COVID-19, being confirmed by RT-PCR testing," said the Health Ministry.
