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Old 06-16-2012, 05:47 AM
 
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Saying its 59-85% effective means somewhere in that range is the percentage of people who won't get it at all if exposed. There is a separate effectiveness rate for serious cases that is higher.
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Old 06-17-2012, 03:19 PM
 
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Kathy, I remember reading that 59-85% effective means the DIFFERENCE between
1) those who get the shot and don't get the disease and
2) those who don't get the shot and still don't get the disease.

So, for example, in the case of flu shots, 59-85% fewer people who've gotten the flu shot get the flu than those who haven't gotten the flu shot--but either way, close to 95% of BOTH groups studied did NOT get the flu.


It does NOT mean that 59-85% who get exposed are protected.

I believe that was according to the Cochrane Collaborative, but am out of town right now, and not able to access the files on my computer where I had that info saved.
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Old 06-17-2012, 03:53 PM
 
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Originally Posted by Taximom5 View Post

Kathy, I remember reading that 59-85% effective means the DIFFERENCE between
1) those who get the shot and don't get the disease and
2) those who don't get the shot and still don't get the disease.
So, for example, in the case of flu shots, 59-85% fewer people who've gotten the flu shot get the flu than those who haven't gotten the flu shot--but either way, close to 95% of BOTH groups studied did NOT get the flu.
It does NOT mean that 59-85% who get exposed are protected.
I believe that was according to the Cochrane Collaborative, but am out of town right now, and not able to access the files on my computer where I had that info saved.

Your post spurred me to look around.

 

This article looked at how efficacy was described, and you are right, it has little to do with how many exposed people got the flu.  

 

If 2% of vaxxed get the flu and 4% of unvaxxed, the efficacy (50%) is the same as if 80% of of unvaxxed people got the flu and 40% of vaxxed did (once again 50%).  Efficacy is measured with attack rate of disease in unvaxxed minus the attack rate of disease in vaxxed divided by disease rate in unvaxxed.  (aru-arv/aru)

 

It was quite the interesting read - one I hope to go back over when I can take it all in.

 

https://www.hidionline.com/hidi/Documents/Vaccine_Epidemiology.pdf

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Old 06-17-2012, 06:25 PM
 
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Well you learn something new everyday.
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Old 06-18-2012, 06:02 AM
 
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That is interesting. So 50% effective means you're half as likely to get it if you get the shot than if you didn't, and 85% effective means you're almost 7 times less likely to get it if vaxxed than unvaxxed.


Mother of two living in UK. Daughter (2007) born in USA, son (2010) born here. I'm pro natural birth, midwife care, breastfeeding, co-sleeping, baby wearing and a keen advocate of cloth diapering. I'm a full time working research scientist (physical sciences) and I'm pro-vaccine.

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Old 06-18-2012, 06:23 AM
 
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That is interesting. So 50% effective means you're half as likely to get it if you get the shot than if you didn't, and 85% effective means you're almost 7 times less likely to get it if vaxxed than unvaxxed.

 

If 9 percent of unvaxxed get a disease, and 1 percent of vaxxed do, the efficacy rate will be 88%  (9-1)/ 9

 

If 90% of unvaxxed get a disease, and 10 % of vaxxed do, the efficacy rate will still be 88%

 

For me, it is important to know the pecentage of people who get the disease in the first place, not just  the efficacy rate.

 

Using the top line, 91% of unvaxxed do not get disease xyz, and 99% of vaxxed do not get xyz, I might be inclined to skip xyz if xyz does not scare me too much in the first place.

 

Using the bottom number (and assuming I have no other issues with vaccines), where I have a 10% chance of getting a disease if vaxxed and a 90% if unvaxxed, I might be more inclined to vax.  

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Old 06-18-2012, 07:47 AM
 
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Originally Posted by kathymuggle View Post

 

If 9 percent of unvaxxed get a disease, and 1 percent of vaxxed do, the efficacy rate will be 88%  (9-1)/ 9

 

If 90% of unvaxxed get a disease, and 10 % of vaxxed do, the efficacy rate will still be 88%

 

For me, it is important to know the pecentage of people who get the disease in the first place, not just  the efficacy rate.

 

Using the top line, 91% of unvaxxed do not get disease xyz, and 99% of vaxxed do not get xyz, I might be inclined to skip xyz if xyz does not scare me too much in the first place.

 

Using the bottom number (and assuming I have no other issues with vaccines), where I have a 10% chance of getting a disease if vaxxed and a 90% if unvaxxed, I might be more inclined to vax.  

Quite right.

 

And if the vaccine has a risk of serious side effects (like Gardasil) or does not stop transmission of a disease (like FluMist or pertussis vaccines), then that weighs into the decision as well.

 

And we have only recently become aware that people can have serious side effects that are not immediately obvious--like autoimmune issues, seizures etc.  Vaccine-induced seizures may occur weeks after the vaccine--which is something most doctors have not been taught.  Certainly, most people are unaware of that possibliity, and if a child has his first-ever seizure 10 days after a vaccine, the parents would never dream that that vaccine might be involved, nor would the doctor, never having been trained to recognize this possibility.  Autoimmune disorders, once triggered, often take weeks or months for their symptoms to be apparent, even after autoimmune activity is clinically apparent. For example, with celiac disease, one can have visible damage to the intestinal villi well before one has noticeable intestinal symptoms.

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Old 06-18-2012, 09:12 AM
 
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Yeah I see you're point. You want to know both the baseline frequency, and the efficiacy of the vaccine in making the choice - not just one or the other. 

 

But I think it makes sense to talk about the rates relative to the unvaccinated population in this way since that figure is about the improvement the vaccine itself offers in avoiding a certain disease (ie. make you half as likely, or 9 times less likely to get the VPD), while the baseline frequency will change with time due to factors like what proportion of the population are immunised/immune, general hygiene etc. 

 

But definitely you want to know both when researching vaccine choices. 


Mother of two living in UK. Daughter (2007) born in USA, son (2010) born here. I'm pro natural birth, midwife care, breastfeeding, co-sleeping, baby wearing and a keen advocate of cloth diapering. I'm a full time working research scientist (physical sciences) and I'm pro-vaccine.

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