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Herd Immunity

(289 Posts)
Tabitha8 Sun 09-Sep-12 16:42:12

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?

LeBFG Mon 17-Sep-12 07:31:20

I think this point about 'significant proportion' needs addressing. I would understand this to mean: a proportion that would have a significant/measurable effect of disease susceptibility in the unimmune. If it were explicitly referring to threshold, they would be emphasising the exact proportion etc.

Bm: explain to us explicitly what your understanding of herd effect is. Do you think that vaccinating 3 in 1000 will have an effect? 400 in 1000, 800 in a 1000?

Tabitha, you ask a good question wrt sources of disease. We brush shoulders with perhaps tens, of people a day (more if you're walking through a shopping mall etc). Still, most of the diseases we vaccinate, although often pretty contagious, are caught laregely from people we have close contact with, very frequently family members. Children have always been very susceptible to disease bacause, amongst other things, they are in close contact with a lot more sources of disease at nursery/school than we are as adults. I reckon my weekly close contacts come to less than ten people (but I live in the country) and even when I was working, you could have added 5 to that number. You may be surprised by how few close contacts people have in a week! Factor in a low vaccination rate - it is quite possible that having one or two of my contacts no longer spreading disease could have a big impact on if I get ill or not.

bruffin Mon 17-Sep-12 08:11:56

I do think there is a difference if you commute somewhere like London LeBFG, you can come into very close contact with a lot of different people on a daily basis
But if you dont have children, drive to work and work in a small office then you really don't need to a lot of people around you to be immune to stop you getting a disease. I know before we had children, dh started to commute for a short while and started picking up one bug after another, which he never did before.

LeBFG Mon 17-Sep-12 08:28:11

Yes indeed bruffin. Lifestyle will make a big difference to your exposure risk. The thing with epidemiological models is they deal in populations writ large, not micro-populations, or families or even individuals. It may seem improbable that a low vaccination rate will have any effect on whether you contract a disease or not, but where an individual isn't seeing too many people and the disease is not super contagious, I can easily imagine a low proportion of vaccinated people making a difference on disease incidence.

bruffin Mon 17-Sep-12 09:30:15

It just plain common sense, not sure why we need huge long threads on it.

Tabitha8 Mon 17-Sep-12 19:00:01

Bruffin It was a health visitor who said to me that I should vaccinate my child in order to maintain herd immunity.
Then we hear the term "herd immunity" in the media whenever there is an outbreak of disease.
Here, on the BBC website, for example, during last May's measles cases, they talk about an uptake rate for the MMR required in order to stop the spread of disease:
www.bbc.co.uk/news/health-13561766
"HPA figures show that the number of toddlers getting the MMR vaccination is climbing steadily, but is still far from the 95% uptake rate needed to stop the spread of the disease in the community."

I think that this thread might, more sensibly, be suggesting that the above approach is too simple? It will vary from area to area and, as BFG said, from circumstance to circumstance?
Yet, there again, I do go on holiday. I travel abroad, I travel within the UK.

ElaineBenes Mon 17-Sep-12 21:28:05

But as we've discussed, while there is indeed a threshold where a disease can't be sustained - even below that threshold, having more immunised children still reduces the probability of a non immune child being exposed to the disease.

Primarily you should vaccinate your child to protect him or her but even if you're below the threshold where a disease won't spread, you can maintain the herd immunity already achieved by keeping vaccination levels up. That must be what your hv meant.

bruffin Mon 17-Sep-12 22:09:36

"HPA figures show that the number of toddlers getting the MMR vaccination is climbing steadily, but is still far from the 95% uptake rate needed to stop the spread of the disease in the community."

Most people reading that would have the common sense to realise that 95% is not an all or nothing figure.

ElaineBenes Mon 17-Sep-12 23:01:51

Not if you want to pretend that herd immunity is a myth so you can keep on claiming that your decision not to vaccinate does not impact anyone else in society.

sashh Tue 18-Sep-12 02:32:05

Elaine

That still does not explain how R>1 can rise to R=1

ElaineBenes Tue 18-Sep-12 11:32:26

R decreases as the number of susceptible people in the population decreases. It doesn't necessarily stop when it equals 1.

Obviously it doesnt rise if you're going from more than 1 to less than 1. I think bm wrote that by mistake?

Tabitha8 Sat 22-Sep-12 21:37:24

Bruffin "Most people reading that would have the common sense to realise that 95% is not an all or nothing figure. "
That's one person here, then, with no common sense, I am afraid.

ElaineBenes Sat 22-Sep-12 23:41:54

Tabutha
Are you still saying that there is no effect on disease transmission if vaccination rates are 90% as opposed to 95%?

Even bm has realised that there is an effect.

LMCG Tue 25-Sep-12 09:11:47

If people are so confident that vaccination works, why are you worried about whether or not other people are vaccinated??? surely you should be protected by said vaccination? herd immunity is shown time and time again to be a complete myth - outbreaks of disease occur in fully vaccinated communities.

ElaineBenes Tue 25-Sep-12 15:08:54

Oh dear, someone's been drinking the crankosphere kool aid.

Have you actually read this thread and the links on it?

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