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In reply to the discussion: An unvaccinated worker set off an outbreak at a U.S. nursing home where most residents were immunize [View all]Buckeye_Democrat
(14,853 posts)... during their trials, with Pfizer & Moderna having stricter definitions while still showing higher efficacy rates. (On the other hand, there were also fewer variants during their trials.)
COVID-19 vaccines: What does 95% efficacy actually mean?
https://www.livescience.com/amp/covid-19-vaccine-efficacy-explained.html
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So, if efficacy means some percent fewer cases of COVID-19, what counts as a "case of COVID"? Both Pfizer and Moderna defined a case as having at least one symptom (however mild) and a positive COVID-19 test. Johnson & Johnson defined a "case" as having a positive COVID-19 test plus at least one moderate symptom (such as shortness of breath, abnormal blood oxygen levels or abnormal respiratory rate) or at least two milder symptoms (such as fever, cough, fatigue, headache, or nausea). Someone with a moderate case of COVID-19 by this definition could either be mildly affected or be incapacitated and feel pretty sick for a few weeks.
Barker cautions that its tricky to directly compare efficacy between the Johnson & Johnson, Pfizer, and Moderna vaccines, because the clinical trials happened in different geographic areas with different populations, and at slightly different time points in the pandemic when different variants of COVID-19 were circulating. There were more people who had the B117 [U.K. variant] or other types of variants during the time of the Johnson & Johnson trial than during the Moderna trial, she said.
And none of the three vaccine trials looked at all for asymptomatic COVID-19. "All these efficacy numbers are protection from having symptoms, not protection from being infected," Barker said. (Some early studies hint that the Pfizer and Moderna vaccines also reduce the number of viral particles in a person's body, called viral load, and the likelihood of testing positive at all, which would cut transmission. Still, because we don't yet know that for sure, people "can't throw away their mask" once they're vaccinated, Barker said.)
But all three trials also used a second, potentially more important, definition of "cases." What we care most about is protecting people from the worst outcomes of COVID-19: hospitalization and death. So Moderna, Pfizer and Johnson & Johnson also measured how their vaccines performed against severe disease (which meant severely affected heart or respiratory rate, the need for supplemental oxygen, ICU admission, respiratory failure or death).
All three vaccines were 100% effective at preventing severe disease six weeks after the first dose (for Moderna) or seven weeks after the first dose (for Pfizer and Johnson & Johnson, the latter of which requires only one dose). Zero vaccinated people in any of the trials were hospitalized or died of COVID-19 after the vaccines had fully taken effect.
"We are incredibly lucky with how effective these vaccines have been," Barker said.
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