Another herd immunity thread - Page 4

[PaigeC]

Originally Posted by carriebft

Some also see a subclincal infection (having been exposed to wild type measles) acts as a natural booster to the vaccine. I don't see subclincal measles as much of an issue and I don't think it happens too often to the point where transmission is possible (or we would have a lot more measles cases and a lot more vaccinated measles cases-- as the case would have to have a high enough viral load to transmit, in which case it would not be too subclincal anymore)

I swear it took me an hour to find these again! I need a folder for all this stuff!

Detection of measles vaccine in the throat of a vaccinated child.
http://www.ncbi.nlm.nih.gov/pubmed/1...t=AbstractPlus
Quote:
Fever occurring subsequent to measles vaccination is related to the replication of the live attenuated vaccine virus. In the case presented here, the vaccine virus was isolated in the throat, showing that subcutaneous injection of an attenuated measles strain can result in respiratory excretion of this virus.

Detection of measles virus RNA in urine specimens from vaccine recipients.
P A Rota, A S Khan, E Durigon, T Yuran, Y S Villamarzo, and W J Bellini
http://www.pubmedcentral.nih.gov/pic...9&blobtype=pdf
Quote:
The changing epidemiology of measles, in the form of mild
measles cases in previously vaccinated individuals (1, 11, 20),
suggests that more asymptomatic or subclinical cases might be
occurring. ... In one previous
study, urine samples from 5 of 12 measles case contacts
were positive for measles virus antigen even though only 1 of
these 5 contacts developed clinical signs

[carriebft]

I am not sure what you are saying. I did not say subclincal infections don't happen, I said that they: possibly beneficial in acting as a booster when exposed to wild type measles and that I don't think subclinical measles are a big issue in creating outbreaks. the one case you noted there is a single case and i would have to see the whole study to really comment on it.

I would add that I don't think we all have subclincal measles either, but I think that is for another thread.

[carriebft]

Also, if subclincal infections were this big issue, why would outbreaks occur from importation in the USA. And if subclincal infections were an issue AND the vaccine didn't work AND the vaccine wanes (as is being said in this thread), wouldn't we be having a lot more measles cases NOT from importation?

[japonica]

Originally Posted by shuttlt

@tmaue
Thanks for explaining that angle on herd immunity so succinctly.


I must confess, when I started looking at the herd immunity that was exactly the problem I had. But (and sticking to measles) I then found the following information from our good friends the CDC.

If you're born prior to 1957 you've probably been exposed to epidemic measles, people vaccinated prior to 1968 needed boosters because they were vaccinated with innactivated measles, post '68 vaccination was with live measles and is believed to be lifelong.
http://www.cdc.gov/vaccines/vpd-vac/...-vac-risks.htm

Just to muddy the waters a bit, here's the Canadian take on adults and measles and the question of immunity...

Combined measles, mumps, rubella vaccine (MMR) is preferred for vaccination of individuals not previously immunized against one or more of these viruses. Adults born before 1970 may be considered immune to measles. Adults born in 1970 or later who do not have documentation of adequate measles immunization or who are known to be seronegative should receive MMR vaccine. One additional dose of vaccine should be offered only to adults born in 1970 or later who are at greatest risk of exposure and who have not already received two doses or demonstrated immunity to measles.

http://www.phac-aspc.gc.ca/im/is-cv/index-eng.php

I was born in 1970, right on fence so to speak (yes, I'm old). I have no idea if I was given the MMR but if I was, I know for certain the mumps portion did not confer "lifelong immunity" as I had full blown wild mumps at age 10. If I never received the MMR, as many in my age group might not have (even Health Canada says we may be considered immune, who knows), then I wouldn't think that as adults we're contributing to "herd immunity." One personal note, even though I have no idea about my measles status, I'm not worrying about it and running out to get a MMR.

[MyBoysBlue]

I'm Canadian and I was born in the later half of the 70's. I did get the one round of MMR as a baby. I also did end up with Mumps anyway at around at 11 or 12. So either I was one of the ones where the vax didn't confer immunity at all or it had worn off by that time.

[japonica]

Hey, maybe we got a bad batch of mumps vaccine...so much for us protecting the herd. LOL.

[PaigeC]

Originally Posted by carriebft

Also, if subclincal infections were this big issue, why would outbreaks occur from importation in the USA. And if subclincal infections were an issue AND the vaccine didn't work AND the vaccine wanes (as is being said in this thread), wouldn't we be having a lot more measles cases NOT from importation?

Perhaps we DO have a lot more measles cases but they are subclinical and/or not diagnosed by drs? When (if) subclinical infection is rampant then the source of outbreaks is difficult to determine.

[mamakay]

Originally Posted by carriebft

Also, if subclincal infections were this big issue, why would outbreaks occur from importation in the USA. And if subclincal infections were an issue AND the vaccine didn't work AND the vaccine wanes (as is being said in this thread), wouldn't we be having a lot more measles cases NOT from importation?

What has me completely convinced that measles is really eliminated is the total and complete lack of measles death in infants. If an infant is deathly ill with a measles-like rash, they're going to test for measles. And in a "post vaccine society" it is infants who are most severely affected by measles when there's an epidemic.

[ema-adama]

Originally Posted by shuttlt

Surely all of these things effect whether or not you get new outbreaks of the disease (well maybe not the polluted air), and maybe how bad you are likely to get it, rather than the possibility of herd immunity?

Yes. This was in relation to epidemic theory, not herd immunity. I am not sure what they are factoring in when they try to figure out what causes an epidemic.

Originally Posted by ema-adama
What makes a susceptible host?

I assume from previous posts, it means 'not immune'. Anyone disagree?

Here something does not make sense to me. I do not think immune/not immune is the only part of the equation. For instance with the various bacteria that can cause meningitis, from what I understand they are in pretty much everyone's throats. But not everyone is coming down with meningitis. Why do some and not others? Why do 999 out of the infected 1000 not develop clinical polio? What makes that one person develop the clinical signs? What makes a person develop complications from measles, chickenpox, mumps?

I think the lifelong immunity claim is only made for live virus vaccination.

Depends who you ask. I have heard the current polio (IPV) and DTaP aurgued as being important from a public health perspective.

Originally Posted by ema-adama
Each vaccine it would seem has a different percentage rate for providing life long immunity (factoring in whether it prevents transmission or only the clinical disease). I have by no means reached a final conclusion as to which vaccines actually do and do not have the potential to confer life long immunity, if any at all.

I'm curious what your reasons are for doubting that vaccines can confer immunity at all, or that the lifelong claim isn't true. Why wouldn't it be?

That was poor phrasing on my part. "if any at all" I meant that I am not sure than any vaccines confer lifelong immunity. I do think some vaccines are more effective than others. I also think that just because a vaccine confers immunity, does not mean that this is preferable to the disease - in light of the extras that come with the vaccine that you would not otherwise need to metabolise. And it does not mean that it is life long immunity.

There were some links to studies posted last night that I still need to read. The source of the lifelong immunity claim is important as so many people seem to doubt it.

One day I hope to have a neat tidy table with each vaccine and the studies done on duration of immunity. So far this eludes me. But this is central to the herd immunity aurgument. Can you imagine the confusion if pediatricians started trying to explain why some vaccines contribute to herd immunity and others do not? The number of times I have seen DTaP given as a vaccine for herd immunity just has my head :

Shifting epidemiology is surely an argument for not having a sloppy vaccination program, rather than an argument about whether herd immunity is achievable, or meaningful. As for serotype/Th1 immune systems, I would need to read more in order to comment.

This is the second time I have read you writing this and it has me intrigued. Why would an optimal vaccination rate take care of shifting epidemiology?

A lot of what you say strikes me as sensible. Vaccination most certainly isn't a substitute for clean drinking water. Having said that, are there figures for how bad these diseases (say measles) are in countries that do have clean drinking water etc...?

I have not done in depth reading on measles as it was never a question for me. I know there are other mama's who have lots of info for this. There was an outbreak in Switzerland that I read about and no one died. I can't remember the complications and I certainly cannot remember what the health profile of those who had complications were. I hope someone has the figures for this question.

Originally Posted by tmaue

One of the questions given above was about why I doubt antibodies, as far as vaccine protection goes. The reason I doubt antibodies is because you see over and over in studies and personal accounts where someone had sufficient antibody levels and still got the disease. You also get the reverse, where someone does not have antibodies and when exposed does not get the disease. There is something else that must be going on in the immune system to make this possible. They are starting to learn more but more info is needed. So, in my opinion, vaccine antibody level alone providing protection is just theory.

Don't say that too loudly Terribly blasphemous.

I think what I was trying to say is that herd immunity is part of epidemic theory as in an attempt at preventing epidemics.

But when you are dealing with infectious diseases that are not dangerous to most people who are healthy and have access to the things we know promote good health, then I find myself asking the question as to why the vaccine is needed to create herd immunity.

What was wrong with the model of children having illnesses that left them immune as adults when the diseases are more dangerous (mumps, measles, rubella, chickenpox)? And, if you were a woman, protecting your child through the placenta and breastmilk. What was not working there?
Surely this was also creating herd immunity?

[mamakay]

Originally Posted by carriebft

The 15 year study seemed to me to say that the projections we thought would happen did not hold and that the MMR continued to be effective. I know I have a 25 year one but I just cannot locate it at the moment.

Some also see a subclincal infection (having been exposed to wild type measles) acts as a natural booster to the vaccine. I don't see subclincal measles as much of an issue and I don't think it happens too often to the point where transmission is possible (or we would have a lot more measles cases and a lot more vaccinated measles cases-- as the case would have to have a high enough viral load to transmit, in which case it would not be too subclincal anymore)

I also think the outbreaks recently demonstrated that the MMR doesn't seem to wane or be waning yet (again, its only been around 40 years). If you look at switzerland and USA particularly, the infection remained isolated to unvaccinated and partially vaccinated populations.

For the measles component, yes. (for now...we did have a lot of measles floating around until the late 90's, and that's probably why those of us vaccinated in the 70's and 80's aren't having our own measles epidemic at the moment. Our vaccine immunity was regularly "boosted" by exposure to the wild virus from time to time in the 80's and 90's.)

The mumps part is different. Pretty much every country on earth that has used the Jeryll-Lynn strain for a long time has seen mumps epidemics in an older age group.

For this reason, the CDC is considering adding a third dose of MMR to the schedule, to be given to adults. Which probably won't hurt the continued elimination of measles, too.

[carriebft]

Actually the Switzerland outbreak does now have a death associated with it. It happened this past month.

[carriebft]

There was an outbreak in Switzerland that I read about and no one died. I can't remember the complications and I certainly cannot remember what the health profile of those who had complications were. I hope someone has the figures for this question.

outbreak in switzerland to date:

Bern noted that since November 2006 Switzerland has seen 3,400 cases of measles, with one death last week in Geneva, 250 hospitalizations and 500 complications that included 143 cases of pneumonia and 8 cases of encephalitis

http://genevalunch.com/2009/02/06/me...erland-update/

outbreak in germany- 614 cases (some traced back to switzerland):

All interviewed patients fulfilled the clinical case definition for measles. Otitis media was reported by 91 (19%) patients, pneumonia by 35 (7%), and encephalitis by three (0.6%), of whom two died. Measles-related complications were more common in younger children: otitis media (22% in infants, 21% in 1–14 year-olds, 10% in > 14 years; P = 0.008) and pneumonia (17% in infants, 7% in 1–14 years, 4% in > 14 years; P = 0.015). The two patients with encephalitis who died were aged 2 months and 2 years; the patient who survived was aged 19 years.

[mamakay]

Originally Posted by carriebft

Actually the Switzerland outbreak does now have a death associated with it. It happened this past month.

It sounds like the "completeness of reporting" in Switzerland is very poor if their reported cases make it look like it's just an outbreak. The CDC now thinks it might have been only 3% of measles cases that were being reported here during the early and mid 90's. If you see a measles death, you have to figure that there are thousands of infections (usually about 5-7 thousand) happening, reported accurately or not.

[carriebft]

well, it's 3,600 or something so far so they are getting up there in numbers reported. i am not sure they are still calling it that

[anewmama]

So what does that say about the alleged 90% drop in measles from 1966- 1968? How many cases were erroneously reported then?

[mamakay]

This is an interesting article, relevant to the question of waning immunity:

http://toronto.ctv.ca/servlet/an/loc...05?hub=Toronto

The end result of the investigation into the durability of immunity in the vaccine age could be a recognition that adults need booster shots to prevent outbreaks of what we now consider childhood diseases. Osterholm, for one, thinks that's likely.

[shuttlt]

Originally Posted by ema-adama

Yes. This was in relation to epidemic theory, not herd immunity. I am not sure what they are factoring in when they try to figure out what causes an epidemic.

On one level it's got to be somebody wandering around with an infectious disease meeting enough people who aren't immune. Everything else is detail

Originally Posted by ema-adama

Here something does not make sense to me. I do not think immune/not immune is the only part of the equation. For instance with the various bacteria that can cause meningitis, from what I understand they are in pretty much everyone's throats. But not everyone is coming down with meningitis. Why do some and not others? Why do 999 out of the infected 1000 not develop clinical polio? What makes that one person develop the clinical signs? What makes a person develop complications from measles, chickenpox, mumps?

I assume this is a question that has an answer. Is there a Doctor in the house?

Originally Posted by ema-adama

Depends who you ask. I have heard the current polio (IPV) and DTaP aurgued as being important from a public health perspective.

I'd have to recheck the numbers to be sure that that was bogus. Does it have the same kind of herd immunity ratio as measles. I'm kind of myopically focused on measles right now.

Originally Posted by ema-adama

That was poor phrasing on my part. "if any at all" I meant that I am not sure than any vaccines confer lifelong immunity.

OK

Originally Posted by ema-adama

I do think some vaccines are more effective than others. I also think that just because a vaccine confers immunity, does not mean that this is preferable to the disease - in light of the extras that come with the vaccine that you would not otherwise need to metabolise. And it does not mean that it is life long immunity.

OK, but a vaccine might be preferable it just isn't necessarily preferable, and vaccines don't necessarily need life long immunity for herd immunity - surely they only need to last long enough.

Originally Posted by ema-adama

Originally Posted by shuttlt

Shifting epidemiology is surely an argument for not having a sloppy vaccination program, rather than an argument about whether herd immunity is achievable, or meaningful. As for serotype/Th1 immune systems, I would need to read more in order to comment

This is the second time I have read you writing this and it has me intrigued. Why would an optimal vaccination rate take care of shifting epidemiology?

OK. This is probably just me not explaining myself properly. Clearly shifting epidemiology is a bad thing IF you haven't reduced the occurrence of the illness you are vaccinating against sufficiently. It might be sufficient if you just end up with fewer negative outcomes. It would certainly be sufficient if the number of older people coming down with the illness post epidemiological shift is less than the number before you started vaccinating. I assume that at least the former case must be true given that we vaccinate. Where the average is doesn't matter in and of itself.

Originally Posted by ema-adama

But when you are dealing with infectious diseases that are not dangerous to most people who are healthy and have access to the things we know promote good health, then I find myself asking the question as to why the vaccine is needed to create herd immunity.

But is good nutrition enough to stop children dying of all these diseases if you ended vaccination? Sure it would help, but you would still have a bunch of dead children.

Originally Posted by ema-adama

What was wrong with the model of children having illnesses that left them immune as adults when the diseases are more dangerous (mumps, measles, rubella, chickenpox)?

You might have to accept a bunch of dead children to avoid a small number of dead adults if this was implemented. Also, in the unvaccinated world, most adults would be immune, but some wouldn't be. I would be interested in seeing numbers, but you might end up with more adults with measles as well.

Originally Posted by ema-adama

And, if you were a woman, protecting your child through the placenta and breastmilk. What was not working there?
Surely this was also creating herd immunity?

Not in the same sense since measles and mumps etc.. were still freely circulating.

[ema-adama]

Originally Posted by mamakay

This is an interesting article, relevant to the question of waning immunity:

http://toronto.ctv.ca/servlet/an/loc...05?hub=Toronto

Nice article. I should be using more google scholar

Originally Posted by shuttlt

On one level it's got to be somebody wandering around with an infectious disease meeting enough people who aren't immune. Everything else is detail

OK, I think I am starting to understand where the differences in our approach come from. From what I understand you would be happy with a world where diseases were wiped out one after another leaving the population safer.
I do not think everything else is detail. I think it is very significant as to just who is at risk of developing complication and/or dying. Disease is a part of life and I am not sure that it can just be eradicated with vaccination (articificially - which I know is a difficult word, but I can't think of another).
I just do not think it is that simple. I still think that when addressing epidemiology and trying to figure out how best to protect a population, there are factors which doctors do not think are essential. It is almost as if some magic wand with no side effects is waved and voila, the disease is eradicated and we are a safer, healthier population. But is this really so?

I assume this is a question that has an answer. Is there a Doctor in the house?

Well, there are a couple of questions. To the first one, you do not need to be a doctor to answer it. Look up serotype replacement and the history of HIB and Prevnar. To the others, I do not have the links, but the info is there. If I have time, I will track them down.

I'd have to recheck the numbers to be sure that that was bogus. Does it have the same kind of herd immunity ratio as measles. I'm kind of myopically focused on measles right now.

As neither pertussis nor polio transmission are prevented (although pertussis is a hotly debated one), these vaccines protect the individual, and not the community. (OPV prevent transmission, but it also causes polio)

OK, but a vaccine might be preferable it just isn't necessarily preferable, and vaccines don't necessarily need life long immunity for herd immunity - surely they only need to last long enough.

When life long immunity is required for herd immunity, what else is long enough? Under what circumstances is a vaccine preferable?

OK. This is probably just me not explaining myself properly. Clearly shifting epidemiology is a bad thing IF you haven't reduced the occurrence of the illness you are vaccinating against sufficiently. It might be sufficient if you just end up with fewer negative outcomes. It would certainly be sufficient if the number of older people coming down with the illness post epidemiological shift is less than the number before you started vaccinating. I assume that at least the former case must be true given that we vaccinate. Where the average is doesn't matter in and of itself.

My understanding of shifting epidemiology is that babies are no longer protected by maternal antibodies and older people are more at risk for the diseases - the two segments of the population that you do not want sick with the diseases are now more at risk. I have to admit that this is more theoretical for me, as I do not have the numbers. This has been discussed here before (of course). If I have time I will try and dig it up.

But is good nutrition enough to stop children dying of all these diseases if you ended vaccination? Sure it would help, but you would still have a bunch of dead children.

Oi, who said stopping vaccination?
What do you know about the nutritional needs of a child sick with measles and the recommended treatment? I have to assume you are thinking, please correct me if I am wronge, that it seems complete quackery to believe that something as simple as nutrition, clean water, clean (not disinfected) home environement etc can make that big of a difference in a healthy child. That it can mean the different between life and disability/death. Especially when there is so much science telling us that vaccines and modern drugs are saving so many millions. I certainly do not expect you to take my word on it.

[mamakay]

I'd have to recheck the numbers to be sure that that was bogus. Does it have the same kind of herd immunity ratio as measles. I'm kind of myopically focused on measles right now.

No. The DTaP and IPV are nothing like the measles vaccine. Neither the pertussis vax nor IPV have any significant effect on making the vaccinated non-infectious.

http://www.polioeradication.org/vaccines.asp

Inactivated polio vaccine (IPV) needs to be injected and works by producing protective antibodies in the blood (serum immunity) - thus preventing the spread of poliovirus to the central nervous system. However, it induces only very low levels of immunity to polivirus locally, inside the gut. As a result, it provides individual protection against polio paralysis but, unlike OPV, cannot prevent the spread of wild polio virus.

Pertussis:

http://www.mothering.com/discussions....php?t=1042918

But measles is different. The theory of herd immunity DOES work perfectly (more or less) with the measles vaccine.

[mamakay]

My understanding of shifting epidemiology is that babies are no longer protected by maternal antibodies and older people are more at risk for the diseases - the two segments of the population that you do not want sick with the diseases are now more at risk. I have to admit that this is more theoretical for me, as I do not have the numbers. This has been discussed here before (of course). If I have time I will try and dig it up.

It's all true, but that's actually a compelling reason to NOT stop vaccinating against measles. Measles is "more deadly" (though less common) in societies that vaccinate.
We've reached a point of no return there with maternal antibodies and infants.