Mumsnet has not checked the qualifications of anyone posting here. If you have any medical concerns we suggest you consult your GP.

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?

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?

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 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.

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 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?

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

Elaine

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

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.

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 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.

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.

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

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

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 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 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.

mathanxiety Sun 16-Sep-12 21:33:03

BM -- 'I don't think it's a 'cliff edge effect'. If you read my posts and my links you'll understand what I'm saying. Do you think that having 3 people in 1000 (a very small proportion) immune will offer any protection to the non-immune? There is a reason why most of these definitions use terms such as 'a significant proportion' you know.'

Again, you are missing the point about different diseases, different means of spreading them, different susceptibility levels in different parts of the community.

Hospital workers and Hepatitis of various kinds is a case in point.

mathanxiety Sun 16-Sep-12 21:28:00

BM, 'waning immunity' means no boosters are being administered. Therefore lack of vaccination remains the issue. The Vanderbilt doctor is only partially right, or you have posted a partial quote. Or you have misparaphrased him.

'While it is possible to argue that 'a little bit of the population are immune' it is not possible to argue that you can have 'a little bit' of herd immunity with the other usage because, as many links and diagrams have pointed out, a significant proportion of the population need to be immune for that to exist. '

Depends on the disease and on the part of the population most susceptible. (See Briffin's post about smallpox in NZ and Aus)

seeker Sun 16-Sep-12 19:41:59

In my head it just works the same with bigger numbers. Imagine a class at school, or a nursery, and imagine 3 out of 30 instead of 1 out of 10. Or 10 out of 100.

Tabitha8 Sun 16-Sep-12 19:06:51

I can follow the 1 person in a group of ten immunity example, but we, in reality, mix with far more than that. They then mix with others.
Now, where am I? I think I'm lost already. grin

seeker Sun 16-Sep-12 18:59:31

Well, I understood myself, Tabitha- don't you understand me?

< image of self as cutter through of jargon collapses about ears>

Tabitha8 Sun 16-Sep-12 18:54:39

You could try explaining it to me. I can't even count on my fingers.

JoTheHot Sun 16-Sep-12 13:23:35

You're explanation is excellent seeker. Bm is still being coy as to whether or not she fully accepts it.

Here is an online simulator you can play with. It shows that increasing the proportion of people who are initially immune, always reduces the proportion of the unimmune people infected in a disease outbreak. The effect of 0.3% immunity is too small too see, but 5% has a visible effect. If you'd like me to talk you through how to use it bm, just ask.

seeker Sun 16-Sep-12 10:06:08

Well, I am an arts graduate who counts on her fingers. But.

It would seem to me to be logical that any level of immunity within a population must by definition reduce the risk of transmission of an infectious illness a bit- simply because that's one less person who might pass it on. So in a group of 10 people, where 9 are immune, the 1 remaining non immune person is not going to catch disease Z from them. If 5 are immune and 5 aren't, the chances are higher, but still lower than if none of the group is immune. So even 1 immune person in the group is going to reduce the probability of catching Z a bit.

Reducing the risk of catching Z is different from eradicating it. Which would mean,in my example, 9 of them being immune so that Z has nowhere to go after it has infected and either killed or conferred immunity on the one non immune person.

Does this make sense, or have I missed something?

bumbleymummy Sun 16-Sep-12 09:45:59

Thanks Jo smile

I don't think it's a 'cliff edge effect'. If you read my posts and my links you'll understand what I'm saying. Do you think that having 3 people in 1000 (a very small proportion) immune will offer any protection to the non-immune? There is a reason why most of these definitions use terms such as 'a significant proportion' you know.

bumbleymummy Sun 16-Sep-12 09:34:01

Lol . I've actually been thinking of Jo as the black knight grin

JoTheHot Sun 16-Sep-12 09:31:28

R could not have equalled 2.9. I made a silly mistake. I used the HIT formula wrong because I'm congenitally innumerate. There is no road between Norwich and Cambridge.

Will you now answer the question?

Do you now accept that vaccinating any proportion of people, no matter how small, will reduce the incidence of that disease in the unvaccinated proportion of people? Or do you still believe that there is a cliff-edge effect, such that the reproductive rate of a disease doesn't influence the incidence of the disease unless it falls to one or below?

Join the discussion

Join the discussion

Registering is free, easy, and means you can join in the discussion, get discounts, win prizes and lots more.

Register now