Herd Immunity

[Tabitha8]

A simple title for what I think is probably a complex subject.

If we have herd immunity to an illness as a result of vaccinating our children, how is that maintained given that we don't vaccinate ourselves, the grandparents, our neighbours, etc?

Agreed EB, I'm not an expert, but I am getting facts direct lol. I think the cocoon idea is an excellent one, and most likely being looked at by those higher up. There must be more to the current outbreak than simply waning herd immunity given the vacc has been given for many years, this should have presented earlier than now. Even the experts agreed they aren't sure why its happened.

The rise in measles is much more easily explained.

This part (from my last link) contradicts what you are saying:

"This critical percentage varies according to the disease, the interactions between members of the population and the vaccine, but 90 per cent is not uncommon. This is herd immunity - the fact that others in the herd or population are vaccinated provides protection to all, whether or not vaccinated themselves."

So does this

"Herd immunity

Herd immunity is the proportion of the population that is immune to a particular infectious disease.

Herd immunity threshold (HIT)

The HIT is the proportion of a population that need to be immune in order for an infectious disease to become stable. If this is reached, for example, due to immunisation, then each case leads to a single new case and the infection will become stable within the population. That is, (R=1).

In addition, if the threshold is surpassed then R

re polio again.
If it broke out here, it wouldn't be a huge worry for me, I have to admit (ought that to be hate to admit?)
I don't know my immunity status to it. If I caught it and had even very bad flu like symptoms, I'd cope.
As I said before, I did know someone who had permanent problems from polio ? she had a limp. Wasn?t there a singer who had it similarly as well?
As Bumbley has pointed out, it's unlikely that I would be left permanently paralysed.

If my child were to join the army as BBB mentioned I?m sure he?d take the advice of army doctors with regard to vaccinations. However, I would expect the army to keep him well nourished and to give him clean water to drink. I?m not sure myself why vaccines ought to be needed in such circumstances, but then my reading over the past three years has only focussed on this country.

Which brings me back to holiday vaccinations. Hmm. As I said, I?d have to look at the country and the list of suggested vaccinations. I know nothing, for example, of cholera. I can?t even spell it. I know that it was dealt with here by providing clean water. I suspect I?d simply not go on the holiday. I?ve had a cholera jab and it was horrendous in terms of what it did to my arm for a day or two. If I were in that situation again, I?d ask myself what the chances were of a tourist ending up with cholera.

I note you didn't quote the mortality rate for respiratory polio. The full quote reads:

---

Without respiratory support, consequences of poliomyelitis with respiratory involvement include suffocation or pneumonia from aspiration of secretions.[56] Overall, 5?10% of patients with paralytic polio die due to the paralysis of muscles used for breathing. The mortality rate varies by age: 2?5% of children and up to 15?30% of adults die.[4] Bulbar polio often causes death if respiratory support is not provided;[39] with support, its mortality rate ranges from 25 to 75%, depending on the age of the patient.[4][60]

I was talking about bulbar, aka respiratory, polio as I made clear upthread. The sort of polio that landed kids in iron lungs.

But hey - you clearly don't believe in it. Go you.

Saying 'respiratory', is misleading because spinal polio can also effect the lungs. Bulbar polio accounts for 2% of paralytic polio cases so if you want to say, '25-75% of the 0.02% of people who contracted bulbar polio died' then go ahead.

BM

The threshold is critical for determining whether a disease will continue to spread in a population or whether it will die out. If 1 person, on average, spreads the disease to less than 1 person, any outbreak will be localized and not sustained. If it is just below 1, the transmission chain will probably be longer than if it is way below 1.

Similarly, even if 1 person spreads to the disease to more than 1 person, herd immunity will affect the rate of spread and the 'peak' of an epidemic. If it is just above 1 the rate of spread will be much slower than if significantly above 1.

You don't even need to 'believe' in vaccinations to understand this. Why, historically, has the average age of infection been high in rural populations compared with urban ones?

Why is this so hard to understand BM?

BM: I read the bit in the first link: "Any vaccine will be more effective at the population level if more people have been vaccinated..." and agreed to that.

"This critical percentage varies according to the disease, the interactions between members of the population and the vaccine, but 90 per cent is not uncommon. This is herd immunity - the fact that others in the herd or population are vaccinated provides protection to all, whether or not vaccinated themselves."

This does in fact describe herd immunity threshold and yes, someone should be refering them to wiki.

For the second quote:
"Herd immunity is the proportion of the population that is immune to a particular infectious disease." Agree completely. When the proportion of the population who are immune is zero, there is zero herd immunity, thus zero protective effect. Simple.

Where did all this begin? As is usual with bm, had to scroll upthread and find the nugget at the heart of the dispute. Bm, you said to me: "I'm not really sure how you can put forward a convincing argument for creating herd immunity with the vaccine knowing that it is even less effective." Despite it being less effective, there is still an effect! How do I know? Because wc was the leading cause of death in babies the 1930's in the UK, just prior to the vaccination campaign! Every country that has introduced a vaccination campaign has seen wc deaths in babies plummet!

Unfortunately, the word 'epidemic' is slippery. It varies depending on the disease being described. Do you have a link that showing the UK is currently experiencing a bona fide epidemic of wc? I would be interested to know. I thought there were localised outbreaks, showing the herd immunity effect to be going strong in many parts of the UK. As the person upthread said, the outbreaks of wc are puzzling as we've had low rates for so long (clearly herd immunity has been doing it's bit for a long time, despite the fact the vaccine doesn't confer life-long immunity). There are clearly multiple factors at work.

Elaine, in order for a disease to become stablein the community, R must be

Sorry- are people saying that they wouldn't be worried if their child was exposed to a disease that could leave them dead, or with varying levels of paralysis? Really?

Seeker, the chances of any of us being hit by a car and being killed/left paralysed are far far greater yet we don't worry about that every day.

Ah, so this is the crux of the matter BM. A person who has been vaccinated is far far far more likely to be immune and therefore not susceptible.

No, it's not 100% but this is all about probabilities. You seem to think it's all or nothing.

Vaccinated people are, on average, less susceptible to a disease than unvaccinated people who have not been exposed to the disease. Agree? You may argue the degree but the concept is solid.

Therefore by vaccinating you reduce the susceptible population. The density of susceptibles is reduced and you reduce the chance of an epidemic starting and, if it does, reduce the severity of the epidemic. Again, you may argue the degree (although it would seem to work with, say, measles) but the maths is solid. Right?

So why do you claim that vaccine induced herd immunity doesn't exist?

Actually, I do worry about it BM. That's why I strap my kids into their car seats.

Hang on, my head's spinning a bit here. Are you saying that vaccination is unnecessary because any one individual is unlikely contract a serious illness in their lifetime? The reason you don't think people should be immunised against polio is because not many people were seriously affected by it? This is a new sort of thinking I haven't come across before.

I sometimes I feel like I've discovered a parallel universe, seeker

It wasn't not many people who were affected by it, it was 1000s a year in UK and 10s of 1000s on the US. Not insignificant numbers.
The risk from vaccinating is far less than the risk of the disease, unless of course you are relying on every one else vaccinating.

I get really incandescent with rage sometimes when I think of mothers in the developing world carrying their children for bloody miles in the hope of vaccinations which might actually give them a chance of reaching adulthood, while us comfortable Westerners burble on about polio being nothing much to worry about.

EB, even your own link talks about reducing the number of susceptibles below a level in order to achieve herd immunity. You seem to talk about herd immunity as if it exists regardless of the number of susceptibles. Is that what you think? That as soon as you have a few immune people in a population then you have herd immunity?

EB, You know you can be hit by a car when you aren't in a car don't you?

Seeker, I get incandescent with rage when I think about mothers having to walk miles to get clean water for their children to drink when we can just turn on our tap. Clean water would save a hell of a lot more lives.

Bruffin, what are you replying to?

"Is that what you think? That as soon as you have a few immune people in a population then you have herd immunity?"

Nobody thinks that.

Do you think that you children are somehow magically protected from the killer diseases that used to fill our church yards?

"Seeker, I get incandescent with rage when I think about mothers having to walk miles to get clean water for their children to drink when we can just turn on our tap. Clean water would save a hell of a lot more lives."

It's not either/or.

I'm pretty sure Theodore Rooseveldt and Michael Flanders had access to clean water. Didn't stop them ending up wheelchair users though.

I'm glad to hear it seeker because plenty of people seem to keep saying 'it's not all or nothing' as if the threshold doesn't even come into it.

'magically protected' no. Less likely to contract and/or be seriously damaged by them due to better nutrition, sanitation and healthcare, yes.

Ian Drury had access to clean water too.

I'm talking about clean water in developing countries as you are well aware. Don't try to belittle their situation. Children are dying every minute because they don't have access to clean water - you can't vaccinate against that.

You are belittling every child that has died or been affected by a vaccine preventable disease with every single post you write.