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?

I wasn't trying to belittle anything. As well you know.

Umm, yes, BM. Even a few people vaccinated would reduce the number of susceptibles - by a very little and probably not enough to really notice when outweighed by huge numbers of susceptibles.

I don't know enough to know if the relationship is linear, I suspect it's more an S shaped relationship but I'm not sure.

Why is this is an issue for you? It's just maths! What shape do you think the relationship has and why (eg flat the whole way and then a little increase?)?

I am indeed aware that we can be hit by a car when not in a car. This is an unavoidable risk in normal modern life. Yet I still continue to strap my children when I put them in a car.

And vaccines are one part of an overall development package to save lives. Clean water is indeed another part, together with antibiotics for pneumonia, and oral rehydration salts for example. They all contribute to the same thing - helping children survive and lead productive and healthy lives.
You may find this article of interest
saving children's lives

Really seeker? I'm talking about women walking miles to get clean water for their children and you talk about Theodore Roosevelt.

I asked if you think that having even a few people immune (or a few less susceptibles if you prefer) means you have herd immunity. Is that what you think?

You might find this interesting.

"1.1 billion people lack access to safe drinking water. 2.6 billion people lack adequate sanitation. 1.8 million people die every year from diarrhoeal diseases, including 90 % of children under 5 . "

Why don't you tell me what you're getting at BM? I answered you above.

I mentioned Theodore Rooseveldt because his case shows that yu can be rich and have access to clean water and sanitation and still end up in a wheelchair because of polio.

If anyone is belittling anyone you are being very dismissive of every child in the developing world killed or crippled by polio.

Am confused? I worry about getting hit by a car every time I walk down a street. My 'immunisation' is that I know the green cross code. It doesn't mean I won't be hit by a car, but it certainly reduces my chances. Same as giving my baby vaccinations does stop them getting diseases but reduces their chances of being harmed by the disease in question.

Isn't that what all parents do? The best they can to reduce the chances of their children coming to harm?

Doesn't stop them that should read, obviously!

No one here has said that safe drinking water is a bad thing! It's not, it's an excellent thing and would indeed save many lives.

And in the Lancet article I linked to, it would save more lives than measles vaccines do.

Vaccines save lives. Clean water saves lives. Both are very good things and something people should be entitled to.

You started a thread on herd immunity and suddenly you want to discuss development priorities???? A little distraction technique going on here methinks.

Sorry, you didn't. Tabitha did. But still, start a new thread on development priorities if you have an issue with poor countries spending money on vaccinating children. Don't try to derail this thread.

Actually polio is a strange disease because the severity actually increases when you have access to clean water and aren't exposed to the disease as an infant.

No you didn't EB. You said it would reduce the number of susceptibles. I said:

" 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?"

So is that that you think? That as soon as you have a few immune people/a few less susceptibles that you have herd immunity?

I am not being dismissive of them at all. I just think your comparison between us sitting here discussing polio when people are walking miles to get polio vaccines is inappropriate. Particularly when you consider how many millions of people are dying from lack of a something like clean water in comparison. If you want to get incandescent about something, get incandescent about that.

Hopefully my last paragraph will explain why I went off in a clean water tangent. If you're going to make comparisons between developed and developing countries there are much more glaring differences than vaccine availability.

"I am not being dismissive of them at all. I just think your comparison between us sitting here discussing polio when people are walking miles to get polio vaccines is inappropriate. Particularly when you consider how many millions of people are dying from lack of a something like clean water in comparison. If you want to get incandescent about something, get incandescent about that."

I genuinely don't understand. This thread is about immunity to disease. Not about clean water. I regularly do "get incandescent" about that as well. But that is not what this thread is about. Please will you stop with the smoke and mirrors and stick to the subject.

Whatever seeker. Maybe we should stay clear of comparisons between developing and developed countries. To put it nicely, it's not exactly a 'fair' comparison.

Why? Because you haven't actually got the insensitivity to tell mothers in developing countries that you don't think they should vaccinate their child against the illness that killed its siblings?

(big sigh)

let's put it this way BM. If you reduce the number of susceptibles, you reduce the probability of transmission of disease. if you reduce them by a little, you reduce the probability by a little.

If you wish to call this 'herd immunity' or 'mathematical models of disease transmission', I don't care. If you have a few people vaccinated you have a little 'herd immunity' - the exact amount would depend on the relationship between the number of susceptibles and disesae transmission.

As I said, I suspect it's S shaped so you probably won't have much of an effect at low levels of vaccination.

It is not a belief system - it's a mathematical model.

The vaccine won't be much use if the child starves to death or dies from drinking contaminated water will it? See how inappropriate you're being? Leave it.

No I won't leave it. You are being ridiculous. And you are diminishing the death of every child who dies of a preventable disease in the developing world. It is shameful that not everyone has access to clean water. Shameful. And it is also, and separately, shameful that children wre not protected from preventable diseases.

EB, your own link talks about reducing the number of susceptible people below a certain threshold in order to achieve herd immunity. You do not have 'a little herd immunity' because you vaccinate a few people. You either have it, because a significant proportion of the population is immune, or you don't.

if you're genuinely interested in modelling the impact on mortality of different interventions (which unfortunately do have to take into account mortality from other causes), you can download this software

LIST

It's actually an important question and one that development professionals consider very carefully - what's the most cost-effective tool for saving lives?

Like I said, I think it's an S shaped relationship. You can indeed have a little 'herd immunity', just not enough to have a significant effect.

The theshold would be the bend in the S. I had a feeling that was what you were getting at. I wish you'd just say, it'd make life easier.

This paper shows the potential impact of even quite low levels of vaccination on herd immunity.
www.ncbi.nlm.nih.gov/pubmed/22778297

I'm being ridiculous? You're comparing us with people living without basic access to food, water,sanitation and healthcare to try to suggest we take vaccines for granted and you think it's an appropriate, valid comparison. Why not take away our access to water, food, sanitation and healthcare and see how we fare even with our vaccines.