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[Off-topic] COVID-19 vaccines: What does 95% efficacy actually mean?

2021-02-18 20:51:04
147 3

HI  MIUI Users,
You have likely heard that Pfizer's COVID-19 vaccine efficacy is 95%, Moderna's is 94% and Johnson & Johnson's is 66%. But what do these numbers mean?
It's not just an academic question. How people understand these numbers affects how they think about the vaccine, whether they get it and how they behave after getting it, all of which have implications for the pandemic on a larger scale.
So how should people interpret these numbers?

"I think it's important for people to understand that this is an extremely effective vaccine," said Brianne Barker, a virologist at Drew Universityin New Jersey, referring to the Pfizer vaccine. "This is much more effective than you might think."

One common misunderstanding is that 95% efficacy means that in the Pfizer clinical trial, 5% of vaccinated people got COVID. But that's not true; the actual percentage of vaccinated people in the Pfizer (and Moderna) trials who got COVID-19 was about a hundred times less than that: 0.04%.
What the 95% actually means is that vaccinated people had a 95% lower risk of getting COVID-19 compared with the control group participants, who weren't vaccinated. In other words, vaccinated people in the Pfizer clinical trial were 20 timesless likely than the control group to get COVID-19.
That makes the vaccine «one of the most effective vaccines that we have," Barker told. For comparison, the two-dose measles, mumps and rubella (MMR) vaccine is 97% effective against measles and 88% effective against mumps, according to the Centers for Disease Control and Prevention (CDC). The seasonal flu vaccine is between 40% and 60% effective (it varies from year to year, depending on that year's vaccine and flu strains),but it still prevented an estimated 7.5 million cases of the flu in the U.S.during the 2019-2020 flu season, according to the CDC.

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 atleast one symptom (however mild) and a positive COVID-19 test. Johnson & Johnson defined a "case" as having a positive COVID-19 test plus atleast 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 it’s 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 atslightly 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 a symptomatic COVID-19. "Allthese 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 likeli hood 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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2021-02-18 20:51:04
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Master Bunny

Sarge7 | from Redmi Note 5

#1

Thanks for article . What most of us who have an interest in vaccines are concerned about is the efficacy as the virus continues to evolve and mutate and how quickly scientists will be able to tweak the genomic code .
   
2021-02-18 23:39:55
The true efficacy of these vaccines is very very important to know. And in fact this 95% business is a ton murkier than we've been led to believe.

“Suspected covid-19”

All attention has focused on the dramatic efficacy results: Pfizer reported 170 PCR confirmed covid-19 cases, split 8 to 162 between vaccine and placebo groups. But these numbers were dwarfed by a category of disease called “suspected covid-19”—those with symptomatic covid-19 that were not PCR confirmed. According to FDA’s report on Pfizer’s vaccine, there were “3410 total cases of suspected, but unconfirmed covid-19 in the overall study population, 1594 occurred in the vaccine group vs. 1816 in the placebo group.”

With 20 times more suspected than confirmed cases, this category of disease cannot be ignored simply because there was no positive PCR test result. Indeed this makes it all the more urgent to understand. A rough estimate of vaccine efficacy against developing covid-19 symptoms, with or without a positive PCR test result, would be a relative risk reduction of 19% (see footnote)—far below the 50% effectiveness threshold for authorization set by regulators. Even after removing cases occurring within 7 days of vaccination (409 on Pfizer’s vaccine vs. 287 on placebo), which should include the majority of symptoms due to short-term vaccine reactogenicity, vaccine efficacy remains low: 29% (see footnote).

If many or most of these suspected cases were in people who had a false negative PCR test result, this would dramatically decrease vaccine efficacy.
2021-02-22 03:29:56

Grand Master Bunny

myrichgoh | from Mi 10 Pro

#3

Thanks for sharing...
2021-02-23 08:54:59
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