What does 95% effective mean

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Atreides Ornithopter
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8:06a, 8/4/21
AG
Not to get into the delta debate but for the "baseline" covid, does 95 % mean 95 out of 100 will not test positive to a lab test or does it mean 95 will not show symptoms?

I had a debate at work about this and a guy claimed it meant not showing symptoms but you could still test positive which his his reasoning for "breakthrough " cases.
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RockOn
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8:08a, 8/4/21
With exposure, you have a 1 and 20 chance of still becoming infected with the virus. Regardless of symptoms.

(correct me if i'm wrong)
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beerad12man
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8:22a, 8/4/21
AG
Neither. If we are talking about efficacy of preventing disease, it means they are 95% MORE effective than not. So if 1000 people were studied in a placebo trial over a given time period, and 100 got the disease. 95% effective would be 5 get it in the vaccinated trial in that same time period.

Not that 5% out of 1000 get it. If it meant 5% of all participants get it, that would be 50. Which would be 50% more effective compared to the placebo trial.
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BlackGoldAg2011
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8:23a, 8/4/21
AG
if we are saying it has a 95% efficacy against infection that means your chances of becoming infected are reduced by 95%.

So for example if you tracked 1,000 un-vaccinated and 1,000 vaccinated people across a given time period, and 100 of those unvaccinated people became infected, for a vaccine with 95% efficacy against infection you would expect 5 vaccinated people to become infected in the same time period.

ha, beerad12man beat me too it
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beerad12man
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In reply to BlackGoldAg2011 • 8:23a, 8/4/21
AG
Copy cat
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BlackGoldAg2011
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In reply to beerad12man • 8:30a, 8/4/21
AG
beerad12man said:
Copy cat
apparently i'm too slow on the keyboard. funny that we chose the exact same numbers in our example
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Zobel
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8:30a, 8/4/21
AG
Verbatim from trials.

Pfizer

Quote:
The first primary end point was the efficacy of BNT162b2 against confirmed Covid-19 with onset at least 7 days after the second dose in participants who had been without serologic or virologic evidence of SARS-CoV-2 infection up to 7 days after the second dose; the second primary end point was efficacy in participants with and participants without evidence of prior infection. Confirmed Covid-19 was defined according to the Food and Drug Administration (FDA) criteria as the presence of at least one of the following symptoms: fever, new or increased cough, new or increased shortness of breath, chills, new or increased muscle pain, new loss of taste or smell, sore throat, diarrhea, or vomiting, combined with a respiratory specimen obtained during the symptomatic period or within 4 days before or after it that was positive for SARS-CoV-2 by nucleic acid amplificationbased testing, either at the central laboratory or at a local testing facility (using a protocol-defined acceptable test).

Major secondary end points included the efficacy of BNT162b2 against severe Covid-19. Severe Covid-19 is defined by the FDA as confirmed Covid-19 with one of the following additional features: clinical signs at rest that are indicative of severe systemic illness; respiratory failure; evidence of shock; significant acute renal, hepatic, or neurologic dysfunction; admission to an intensive care unit; or death.
Moderna
Quote:
The primary end point was the efficacy of the mRNA-1273 vaccine in preventing a first occurrence of symptomatic Covid-19 with onset at least 14days after the second injection in the per-protocol population, among participants who were seronegative at baseline....Covid-19 cases were defined as occurring in participants who had at least two of the following symptoms: fever (temperature 38C), chills, myalgia, headache, sore throat, or new olfactory or taste disorder, or as occurring in those who had at least one respiratory sign or symptom (including cough, shortness of breath, or clinical or radiographic evidence of pneumonia) and at least one nasopharyngeal swab, nasal swab, or saliva sample (or respiratory sample, if the participant was hospitalized) that was positive for SARS-CoV-2 by reverse-transcriptase-polymerase-chain-reaction (RT-PCR) test.
...
A secondary end point was the efficacy of mRNA-1273 in the prevention of severe Covid-19 as defined by one of the following criteria: respiratory rate of 30 or more breaths per minute; heart rate at or exceeding 125 beats per minute; oxygen saturation at 93% or less while the participant was breathing ambient air at sea level or a ratio of the partial pressure of oxygen to the fraction of inspired oxygen below 300 mm Hg; respiratory failure; acute respiratory distress syndrome; evidence of shock (systolic blood pressure <90 mm Hg, diastolic blood pressure <60 mm Hg, or a need for vasopressors); clinically significant acute renal, hepatic, or neurologic dysfunction; admission to an intensive care unit; or death. Additional secondary end points included the efficacy of the vaccine at preventing Covid-19 after a single dose or at preventing Covid-19 according to a secondary (CDC), less restrictive case definition: having any symptom of Covid-19 and a positive SARS-CoV-2 test by RT-PCR

95% means if you split a group randomly and give the vaccine to one half and placebo to the others, and you get 100 cases per the definition above, 95 will be in the control group and 5 will be in the vaccine group.
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Atreides Ornithopter
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8:38a, 8/4/21
AG
But the definition of a positive case is a lab test positive? which means not necessarily showing symptoms .

That was what surprised me about his argument not what all of you guys focused on in my post.
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Zobel
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In reply to Atreides Ornithopter • 8:44a, 8/4/21
AG
It depends. Case definition is a moving target. The CDC wants a unified national case definition to try to keep things straight. This may or may not be the same definition of case used in any particular study or paper.

The case definitions to determine efficacy for the vaccines are defined in each efficacy paper.

The CDC case definition can be read here. It's broader, and if I'm reading it correctly can be determined by infection alone. The CDC says probable / confirmed are any one of the following:
Quote:
  • Meets clinical criteria AND epidemiologic linkage with no confirmatory laboratory testing performed for SARS-CoV-2
  • Meets presumptive laboratory evidence
  • Meets vital records criteria with no confirmatory laboratory evidence for SARS-CoV-2

Any cases and deaths classified as probable are included in CDC case counts. The same applies to any cases and deaths classified as confirmed.


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BlackGoldAg2011
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In reply to Atreides Ornithopter • 8:49a, 8/4/21
AG
Baron Von Flag Smasher said:
But the definition of a positive case is a lab test positive? which means not showing necessarily showing symptoms .

That was what surprised me about his argument not what all of you guys focused on in my post.
that's because you're title asked about the definition of efficacy (which if zobel's post is correct, means beer and I are slightly off on our definition)

as to the argument, that depends. This is why you see multiple efficacy numbers listed with varying effectiveness against, infection, disease, hospitalization, etc. If the efficacy is 95% against Infection that means symptomatic or not if you randomly tested a large population this is the effectiveness you would expect to find. if that 95% is against disease (meaning has symptoms) then yes, if you were randomly testing regardless of symptoms you would expect to see a higher case count in the vaccinated group than that 95% would suggest.
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Teslag
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In reply to Atreides Ornithopter • 9:48a, 8/4/21
AG
Baron Von Flag Smasher said:
But the definition of a positive case is a lab test positive? which means not necessarily showing symptoms .

That was what surprised me about his argument not what all of you guys focused on in my post.

I believe the efficacy studies determined it to be symptomatic covid.
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Troglodyte
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12:15p, 8/8/21
AG
If it's a comparison to unvaccinated, the more unvaccinated people get Covid and recover, the lower the efficacy of the vaccines?? Or, is it always compared to previously not infected, unvaccinated?
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Zobel
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In reply to Troglodyte • 12:33p, 8/8/21
AG
It's a comparison versus placebo in that trial - at that time and place, those people, etc. so that number is fixed.

The studies are limited, and you can't really extend them beyond what they actually studied. Other studies have found similar numbers though.
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Nasreddin
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1:35p, 8/8/21
Nasreddin
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1:36p, 8/8/21
It means whatever they want it to mean, and will change what it means when it suits them.
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GenericAggie
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In reply to Zobel • 4:36p, 8/8/21
AG
I don't follow. Not at all.

Does the vaccine prevent me getting the virus?

The latest narrative is that the vaccine does not stop you from getting the virus. It keeps you from getting really sick.

How are we defining efficacy at this stage?
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Nasreddin
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In reply to GenericAggie • 4:39p, 8/8/21
Well, i was vaccinated for small pox as a kid. I only caught a little and was only slightly disfigured. Yeah...I also passed small pox to all my family, but it was a great vaccine. Lol.


Apply the "reasoning" and goal post moving of these ideologues to any other vaccine and you'll see how stupid it is.
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Zobel
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In reply to GenericAggie • 4:50p, 8/8/21
AG
When they talk about efficacy they're always citing a study, which means you can only apply it so far out of a study.

The endpoints of the vaccine studies which were done late last year were symptomatic covid, and severe covid. I put the Pfizer and Moderna studies up there. So when people say 95%, they are referencing those studies or studies like those.

If you ask about being infected but not sick, I guess you'd define that as being PCR positive but no symptoms. I don't think any of the vaccines tested for that... because it doesn't really matter, in a practical sense, and it's much more difficult to do. You'd have to periodically test everyone, regardless of symptoms.

But they did test for people who had any one of those symptoms, plus being PCR positive. In those tests (which were pre-delta) you were roughly 19 times more likely to get sick - any of the symptoms plus PCR positive - without the vaccine than with.

To re-define efficacy, you'd have to do another study, like say Pfizer efficacy vs delta, and then that efficacy number would be again compared to something. This study did what's called a test-negative design* to do just that, and found that against the alpha variant it was 93% effective and against delta 88% compared to not taking the vaccine. Efficacy is always relative to something, so should always be talking about some study, trial, whatever.

The media shorthand for 95% is just sort of lumping all these into a basket and hand-waving at them. It sounds science-ier than saying "really effective" or "big numbers".

*Test negative is a different style of studies than the phase 3 trials, because instead of starting with a test (vaccinated) and a control (placebo), you count everyone who presents with symptoms that match your case criteria (in this case having covid) then find out afterwards which patients are your test group (vaccinated) and which are your control (unvaccinated). Common for monitoring for vaccine efficacy.
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Zobel
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In reply to Nasreddin • 4:53p, 8/8/21
AG
These vaccines and smallpox are actually similar..
Quote:
...more than 95% of individuals develop a 'take' with neutralizing antibodies after primary vaccination. The efficacy of the vaccine has not been evaluated in controlled studies, but epidemiologic data suggest that a high level of protection persists for up to 5 years after vaccination, with partial immunity persisting for 10 years or more. The vaccine will prevent infection or reduce the severity of illness if given within a few days following exposure to smallpox.
Most of the vaccines we have on our current schedule have efficacy numbers in the 90s, many require multiple doses to get there (MMR, Polio, DTaP, etc all have multiple doses).
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GenericAggie
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In reply to Zobel • 6:23p, 8/8/21
AG
Put all of that into 1 sentence because you really didn't clarify anything. I'm not being an ass.

One question:

1. Does the vaccine BLOCK me from getting the virus?

I'm vaccinated btw.
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Zobel
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In reply to GenericAggie • 6:34p, 8/8/21
AG
That's called sterilizing immunity. These vaccines probably don't, but they weren't justified based on that, and the trials above weren't even testing for that.

And even if they do, they may provide sterilizing immunity for a period of time, and then it may wear off.

Most vaccines we use don't provide sterilizing immunity, and if they did, a mutation may make that moot anyway.

As an aside:
If you want to be precise about the numbers, they are limited to the test you did. If someone says,
"how effective is this vaccine?" to be strict the answer should be "when they tested it in study x they found it to be y% effective vs z control."

The minute you change anything about study x - location, demographics, what virus variant was circulating - that original y% number is no longer directly applicable. That's life. So when delta came around, all bets are off (but they redid testing about found that if Pfizer was 93% effective vs alpha, it's around 88% effective vs delta, all things being equal).
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cc_ag92
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In reply to GenericAggie • 6:50p, 8/8/21
AG
The vaccine doesn't block you from getting the virus. The more the virus is in the community, the greater your chance is of getting it, even with the vaccine. The vaccine will protect you from severe illness. This is the message I heard from the very beginning. I'm not sure how others didn't understand it. I was very optimistic at that point because I thought most people would get it.

Nebraska Medicine:
"Efficacy and effectiveness sound similar, but they are not the same. Efficacy refers to how well a vaccine performs under ideal conditions as reflected in a careful clinical trial. For instance, the study participants are carefully chosen and given specific instructions to reduce their risks, the vaccine doses are given at precisely the right time and subjects are monitored closely.
Effectiveness, on the other hand, refers to what happens in the real world when a vaccine is employed to protect a community, and often is discussed in terms of community-wide protection. When you get the yearly influenza shot, for instance, you may still get sick with one of several strains of flu that year. But, being vaccinated means protection against a more severe case. Likewise, if enough of your neighbors also took the flu vaccine, your ICU will not see as many influenza cases. People at higher risk may avoid the disease entirely. Vaccine effectiveness is about how protected everyone is as a whole.
"Vaccine effectiveness is what happens to the community experience with a disease," says Dr. Brett-Major. "So, on a population level, when you have a lot of vaccine uptake, it does change the community experience with a disease. Vaccines with moderate and even low efficacy can have reasonable effectiveness." '
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GenericAggie
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In reply to Zobel • 7:15p, 8/8/21
AG
Effective in what? Stopping someone from getting the virus or from getting hospitalized?
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GenericAggie
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In reply to cc_ag92 • 7:16p, 8/8/21
AG
Because that's not what the cdc or Fauci said. Let's go find some press conferences and interviews.
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Zobel
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In reply to GenericAggie • 7:20p, 8/8/21
AG
In all cases I've linked here vaccine effectiveness is against symptomatic disease.
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Fitch
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8:35p, 8/8/21
AG
I really don't understand the drive to find a conspiracy where one doesn't exist.
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cc_ag92
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In reply to GenericAggie • 8:50p, 8/8/21
AG
Like Pfizer's vaccine, Moderna's seems to be highly effective about 94% at preventing symptomatic SARS-CoV-2 infections. Its safety profile is also similar to Pfizer's, with fatigue, headaches and pain at the site of injection among the most often cited side effects. Nature Dec. 18, 2020

Another unanswered question is whether the vaccines, whose trials have shown that they prevent people from getting seriously ill and dying of COVID-19, also prevent people from becoming infected in the first place and, importantly, from passing the virus on to others. It could be the case, Fauci said, that even if the vaccines don't prevent infection, they keep virus levels so low that they do prevent transmission. The Harvard Gazette December 10, 2020

Fauci: "Ratio is 94% to 95% efficacious in preventing clinical disease. It would be terrible, with a tool as good as that, if people don't utilize that tool." and

"MARTIN: How many Americans, Dr. Fauci, need to get vaccinated before we start noticing an impact on infection rates?

FAUCI: Well, I mean, I would say 50% would have to get vaccinated before you start to see an impact. But I would say 75% to 85% ratio would have to get vaccinated if you want to have that blanket of herd immunity - namely, so many people getting vaccinated that the virus really doesn't have any place to go. Essentially, what we did with measles in this country, what we did with polio in this country - if you get that level of herd immunity, you could essentially crush this outbreak in this country." NPR, December 2020

I'm not going to search more. If you want to find something else, go ahead, but the first three articles I pulled from December 2020 didn't state that the vaccine eliminates one person's ability to catch the virus. The vaccines do lessen one's chance of catching it compared to an unvaccinated person. The rate of community spread impacts one's chance. What I do know is that when we were vaccinated early on, we didn't believe that there was no way we would ever catch Covid. We did believe that we improved our odds based on the research we did.
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KidDoc
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11:21a, 8/9/21
AG
You have to realize that this spike is 90% + due to delta variant. The mRNA vaccines generate an immune response to a specific spike protein that is slightly different in delta thus allowing the virus to evade immunity temporarily.

The approval studies were done pre-delta variant and that is the reason for the difference in primary prevention with the new data coming out of England, Israel, and Mass.

It sucks but that is what seems to be the case. The data is being churned daily and it does seem like vaccine decreases your risk of getting any symptoms at all with Delta but not near the 95% of the original studies. And it is clear that they decrease the risk of hospitalization and death.
No material on this site is intended to be a substitute for professional medical advice, diagnosis or treatment. See full Medical Disclaimer.
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Diyala Nick
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In reply to KidDoc • 12:31p, 8/9/21
AG
KidDoc said:
You have to realize that this spike is 90% + due to delta variant. The mRNA vaccines generate an immune response to a specific spike protein that is slightly different in delta thus allowing the virus to evade immunity temporarily.

The approval studies were done pre-delta variant and that is the reason for the difference in primary prevention with the new data coming out of England, Israel, and Mass.

It sucks but that is what seems to be the case. The data is being churned daily and it does seem like vaccine decreases your risk of getting any symptoms at all with Delta but not near the 95% of the original studies. And it is clear that they decrease the risk of hospitalization and death.


Hold your horses there Doc. Someone with a degree in Business Management and access to YouTube has information you may not be privy to.
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Gordo14
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In reply to GenericAggie • 12:34p, 8/9/21
GenericAggie said:
Because that's not what the cdc or Fauci said. Let's go find some press conferences and interviews.


What did you want him to say? "The vaccine is 95% effective at preventing symptomatic Covid-19, but a new variant that doesn't exist yet will decrease that effectiveness to something more like 70-80%. That same variant, which does not exist yet, will be 10x more contagious than the current strain as well."

Is he really expected to know every twist and turn this pandemic will take before they happen. If he did, I'm sure you'd have conspiracies about that too.
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GenericAggie
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In reply to Gordo14 • 8:43p, 8/9/21
AG
Let me say it slowly for those that just want to argue.

They said the vaccine would STOP the virus from infecting people. That's NOT what the vaccine does.

They said 95% efficacy and stated that meant 95% would not get the virus.

They didn't say - EVER - that you would still get the virus.

NOBODY thought that's what they meant.
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GenericAggie
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In reply to Fitch • 8:46p, 8/9/21
AG
I'm not looking to find a conspiracy. What they said efficacy meant and what it means are different things. My parents didn't get the vaccine to get less sick. Show me ANY press or news headlines or interviews where they describe the vaccine that way.

We never told people to get the vaccine to get less sick.

Remember the phrase - stop the spread? Think about that and what it implies.
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GenericAggie
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In reply to cc_ag92 • 8:49p, 8/9/21
AG
You believed you had a 95% chance of not getting the virus. Isn't that what most people thought efficacy meant?

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Diyala Nick
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In reply to GenericAggie • 9:08p, 8/9/21
AG
GenericAggie said:
I'm not looking to find a conspiracy. What they said efficacy meant and what it means are different things. My parents didn't get the vaccine to get less sick. Show me ANY press or news headlines or interviews where they describe the vaccine that way.

We never told people to get the vaccine to get less sick.

Remember the phrase - stop the spread? Think about that and what it implies.


What do you think "reduction in symptomatic disease" means? It is not the fault of the medical and/or scientific community that you are easily confused.
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GenericAggie
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In reply to Diyala Nick • 9:09p, 8/9/21
AG
I'm far from easily confused, Dick head.

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