Covid-19 vaccine efficacy?

[Unveiled Artist]

I was simply trying to suggest belt-and-braces (and possibly cycle clips) was the best approach. The more the merrier. Hey, I've had the vaccine why do I need to gel my hands?

Maybe there's a balance?

I know hospital doctors wear shields, gloves, a gown, vaccinated, wash their hands when they take the gloves off, and sanitize. We can actually do the same thing, but I guess there's a balance between protecting oneself and going overboard if the need wasn't warranted?

 

[Lyndon]

There will never be herd immunity as long as a sizable portion of idiots refuse to get vaccinated or wear masks

 

[ronki23]

Vaccine efficacy, effectiveness and protection

I have difficulty understanding this as I have a learning disability (autism)

@ChristineM

If you have nothing constructive to say then don't say it at all

 

[ChristineM]

Vaccine efficacy, effectiveness and protection

I have difficulty understanding this as I have a learning disability (autism)

@ChristineM

If you have nothing constructive to say then don't say it at all

Public thread, and in my view my post was constructive. I simply do not believe people's deliberate ignorance over basic hygiene and sanitary procedures.

 

[Altfish]

If a vaccine reduces likelihood of getting Covid-19 then why are we still recommended to wear masks after vaccination ?

If 100 people were vaccinated from Covid then 66 (Janssen) to 95 (Pfizer / Moderna) won't get Covid and 5 to 33 out of that 100 will.

They say herd immunity is 60 to 75% so if 60- 75 people were vaccinated then out of 100 people 40 (66% Janssen efficacy x 60 percent jabbed) to 67.5 (95% Pfizer / Modern x 75 percent jabbed) won't get it.

That still means 32.5 to 60 % of people will still get Covid regardless of whether they are or aren't vaccinated because the vaccines are not 100% effective.

If sample size is 100 then 32.5-60 x 3% means instead of 3 people out of 100 dying from Covid, 2 will die from Covid after jabbing 60-75%.

Have I made an error in my calculations somewhere ?

Good grief!!!
No one has ever said the vaccine will prevent you from getting COVID; what it does very well is stop you getting it badly, ie needing hospitalisation or death.
The number of people dying from COVID after being vaccinated is minimal; in UK nearly all hospitalisations are unvaccinated; deaths of vaccinated people are insignificant.

 

[metis]

If a vaccine reduces likelihood of getting Covid-19 then why are we still recommended to wear masks after vaccination ?

If 100 people were vaccinated from Covid then 66 (Janssen) to 95 (Pfizer / Moderna) won't get Covid and 5 to 33 out of that 100 will.

They say herd immunity is 60 to 75% so if 60- 75 people were vaccinated then out of 100 people 40 (66% Janssen efficacy x 60 percent jabbed) to 67.5 (95% Pfizer / Modern x 75 percent jabbed) won't get it.

That still means 32.5 to 60 % of people will still get Covid regardless of whether they are or aren't vaccinated because the vaccines are not 100% effective.

If sample size is 100 then 32.5-60 x 3% means instead of 3 people out of 100 dying from Covid, 2 will die from Covid after jabbing 60-75%.

Have I made an error in my calculations somewhere ?

Masks provide an extra layer of protection, plus this Delta variant is so contagious that it has changed the "game" somewhat, as a 70% vaccination rate by itself will not lead to herd immunity.

 

[metis]

I withdraw my analogy.
Get the vaccine, wear a mask, wash your hands, stay 2m apart. And this 18 months into it.

Namaste.

 

[Secret Chief]

Namaste.

Prego.

 

[sun rise]

How does herd immunity percentage relate to vaccines not working 100%?

Herd immunity is a measure of how much a disease such as Covid spreads. And what you mean by "not working 100%" is also important.

To take the second part first, vaccines ideally prevent 100% of infections. That is not the case for COVID delta. The vaccine makes it less likely you'll catch the virus, that it will be a serious infection and most importantly that you won't die from it.

That people with the vaccine can still catch the virus means that herd immunity becomes harder and maybe impossible depending on the percentage of of breakthrough cases there are.

I read the other day that delta is so strong that even if 100% were fully vaccinated, we'd still have Covid cases until a new version of the vaccine is available.

 

[Martin]

How does herd immunity percentage relate to vaccines not working 100%?

Herd immunity develops when around 80% of the population develop resistance to an infection, either from vaccination or from previous infection.
It means the "R" number reducing to below 1.

 

[exchemist]

Vaccine efficacy, effectiveness and protection

I have difficulty understanding this as I have a learning disability (autism)

@ChristineM

If you have nothing constructive to say then don't say it at all

It's a good thing you have told us about your disability. Without knowing that it would be easy to get annoyed.

The UK studies suggest that against the Delta variant, which is now dominant in the UK and is far more infectious than the original strain, the vaccines are 90% effective at preventing severe disease - the kind that gets you sent to hospital. That means your chance of severe disease if you are vaccinated is reduced to 10% of what it would otherwise be.

However, your chance of testing positive for the virus, i.e. getting infected, is only halved by the vaccine. That means you can still catch it and can still spread it, though the chance is reduced by half. So masks, which reduce the chance of an infectious person spreading it to others, are still a good idea.

Given that the vaccines only halve the infection rate, and presumably only halve the transmission rate, and given the high R0 number for the Delta variant, it is very hard indeed to reach herd immunity. My own view is that we will have to live with covid circulating along with colds and flu, as just another respiratory diseases you can catch. However, if everyone has either been vaccinated or has some immunity from previous infection, an individual's chance of needing to go to hospital with it will be fairly low. So we may be able to just put up with it.

Unhappily, this likely state of affairs mean that there will continue to be the potential for new variants to be bred in the population. So we may well be constantly playing catch-up, with tweaked vaccine boosters, just as we have to with 'flu'.

 

[exchemist]

Herd immunity develops when around 80% of the population develop resistance to an infection, either from vaccination or from previous infection.
It means the "R" number reducing to below 1.

The % needed for herd immunity depends on R0. With the Delta strain, R0 could be as high as 7, which would put the herd immunity threshold at close to 90% if immunity were 100% effective i.e. total. Given that immunity is only 50% effective against being infected, herd immunity seems to be unattainable.

 

[Polymath257]

If a vaccine reduces likelihood of getting Covid-19 then why are we still recommended to wear masks after vaccination ?

If 100 people were vaccinated from Covid then 66 (Janssen) to 95 (Pfizer / Moderna) won't get Covid and 5 to 33 out of that 100 will.

That isn't what the effectiveness means.

They say herd immunity is 60 to 75% so if 60- 75 people were vaccinated then out of 100 people 40 (66% Janssen efficacy x 60 percent jabbed) to 67.5 (95% Pfizer / Modern x 75 percent jabbed) won't get it.

That isn't what herd immunity means. Even if it *did* mean that, you multiplied the wrong numbers.

That still means 32.5 to 60 % of people will still get Covid regardless of whether they are or aren't vaccinated because the vaccines are not 100% effective.

If sample size is 100 then 32.5-60 x 3% means instead of 3 people out of 100 dying from Covid, 2 will die from Covid after jabbing 60-75%.

Have I made an error in my calculations somewhere ?

Pretty much everywhere.

 

[Polymath257]

So the herd immunity of 60-75% is nonsensical ? It must be higher ?

Herd immunity doesn't mean what you seem to think it means. That 60-75% is the percentage of the population that needs to be resistant in order for the virus not to spread uncontrollably. It says NOTHING about what percentage of the people are naturally immune.

 

[ronki23]

That isn't what the effectiveness means.



That isn't what herd immunity means. Even if it *did* mean that, you multiplied the wrong numbers.



Pretty much everywhere.

It's a good thing you have told us about your disability. Without knowing that it would be easy to get annoyed.

The UK studies suggest that against the Delta variant, which is now dominant in the UK and is far more infectious than the original strain, the vaccines are 90% effective at preventing severe disease - the kind that gets you sent to hospital. That means your chance of severe disease if you are vaccinated is reduced to 10% of what it would otherwise be.

However, your chance of testing positive for the virus, i.e. getting infected, is only halved by the vaccine. That means you can still catch it and can still spread it, though the chance is reduced by half. So masks, which reduce the chance of an infectious person spreading it to others, are still a good idea.

Given that the vaccines only halve the infection rate, and presumably only halve the transmission rate, and given the high R0 number for the Delta variant, it is very hard indeed to reach herd immunity. My own view is that we will have to live with covid circulating along with colds and flu, as just another respiratory diseases you can catch. However, if everyone has either been vaccinated or has some immunity from previous infection, an individual's chance of needing to go to hospital with it will be fairly low. So we may be able to just put up with it.

Unhappily, this likely state of affairs mean that there will continue to be the potential for new variants to be bred in the population. So we may well be constantly playing catch-up, with tweaked vaccine boosters, just as we have to with 'flu'.

Where does it say that testing positive for CoVid19 is only halved by vaccination ?

@Polymath257 can you please correct the calculations because I don't know where I went wrong

 

[Shakeel]

in UK nearly all hospitalisations are unvaccinated; deaths of vaccinated people are insignificant.

"From July 19 to August 2, 55.1 percent of the 1,467 people hospitalised with the Delta variant were unvaccinated, PHE said, while 34.9 percent – or 512 people – had received two doses."
In England, hundreds of vaccinated people hospitalised with Delta

 

[Polymath257]

Vaccine efficacy, effectiveness and protection

I have difficulty understanding this as I have a learning disability (autism)

@ChristineM

If you have nothing constructive to say then don't say it at all

What parts are you finding difficult to understand?

So, to determine the efficacy of a vaccine, we compare the rates of infection for vaccinated people to those for unvaccinated people.

So, suppose we have 1000 vaccinated people and 1000 unvaccinated people. Suppose that among the unvaccinated people, 200 got sick and among the vaccinated people 20 got sick. We compare the 20 to the 200 and find that the number of vaccinated people who get sick is 10% of the number of unvaccinated people who get sick. That gives a vaccine effectiveness of 100%-10%=90%. (These are made up numbers to explain the concept).

From the site you gave: "An efficacy of 80% does not mean that 20% of the vaccinated group will become ill. " It means that given equal numbers of vaccinated and unvaccinated people, the number of vaccinated that get sick will be 20% of the number of unvaccinated people who get sick.

The difference between effectiveness and efficacy is the difference between working in the broader population and working in a clinical trial.

In both cases, the actual number of people who get sick depends on many more things than just whether they have been vaccinated. For example, if someone is never around other people, they won't get sick simply because they are never exposed. Being exposed for a short time while masked is a lot different than being exposed for hours while unmasked. And, among other things, the total number of people who carry the virus affects how likely it is to be exposed at all.

Herd immunity happens when enough people are resistant, either from vaccinations or from immunity produced by exposure, that it is unlikely the virus will be able to go from one infected person to someone who is not resistant.

So, imagine 100% of people are totally resistant to the virus. Then the virus will simply not be able to move to anyone new and will die out. It gets ore complicated when people are not totally resistant and when fewer than 100% of the people show resistance. The key is how likely it is for the virus to go from one infected person to someone new who will become a carrier. The number of people who are likely to get the virus from a single person depends on a lot of factors, but is called the R0 of the infection. if R0 is less than 1, the infection will die out. if it is larger than 1 it will spread faster and faster. herd immunity happens when R0 goes less than 1.

 

[Polymath257]

Where does it say that testing positive for CoVid19 is only halved by vaccination ?

@Polymath257 can you please correct the calculations because I don't know where I went wrong

There is no way to correct the calculations based on the information you have. See my other post.

 

[ronki23]

There is no way to correct the calculations based on the information you have. See my other post.

What parts are you finding difficult to understand?

So, to determine the efficacy of a vaccine, we compare the rates of infection for vaccinated people to those for unvaccinated people.

So, suppose we have 1000 vaccinated people and 1000 unvaccinated people. Suppose that among the unvaccinated people, 200 got sick and among the vaccinated people 20 got sick. We compare the 20 to the 200 and find that the number of vaccinated people who get sick is 10% of the number of unvaccinated people who get sick. That gives a vaccine effectiveness of 100%-10%=90%. (These are made up numbers to explain the concept).

From the site you gave: "An efficacy of 80% does not mean that 20% of the vaccinated group will become ill. " It means that given equal numbers of vaccinated and unvaccinated people, the number of vaccinated that get sick will be 20% of the number of unvaccinated people who get sick.

The difference between effectiveness and efficacy is the difference between working in the broader population and working in a clinical trial.

In both cases, the actual number of people who get sick depends on many more things than just whether they have been vaccinated. For example, if someone is never around other people, they won't get sick simply because they are never exposed. Being exposed for a short time while masked is a lot different than being exposed for hours while unmasked. And, among other things, the total number of people who carry the virus affects how likely it is to be exposed at all.

Herd immunity happens when enough people are resistant, either from vaccinations or from immunity produced by exposure, that it is unlikely the virus will be able to go from one infected person to someone who is not resistant.

So, imagine 100% of people are totally resistant to the virus. Then the virus will simply not be able to move to anyone new and will die out. It gets ore complicated when people are not totally resistant and when fewer than 100% of the people show resistance. The key is how likely it is for the virus to go from one infected person to someone new who will become a carrier. The number of people who are likely to get the virus from a single person depends on a lot of factors, but is called the R0 of the infection. if R0 is less than 1, the infection will die out. if it is larger than 1 it will spread faster and faster. herd immunity happens when R0 goes less than 1.

Why can't we agree on what percentage needs to be vaccinated for herd immunity? Some say 60%, others say 66%, some say 75%

 

[Trailblazer]

Huh? I don't understand that statement. Vaccines prevent illness or make it milder just like seatbelts do for auto crashes.

Unveiled Artist said: ↑
No, but if someone gave you a pill that just came off the market to prevent an illness you don't know you have (yet?) that's different than just seatbelts and antilock breaks.

The reason they are different is because seat belts have no potential to cause any harm (similar to wearing a mask to prevent getting Covid) whereas vaccines do have the potential to be harmful, and that is why under normal circumstances vaccines are rigorously tested for both safety and efficacy for 6-10 years before they are approved by the FDA. How long were the Covid vaccines tested?