Herd immunity for dummies

amother

Tue, Feb 23 2021, 8:04 pm

I still don't get it and hope someone here can explain it to me.

I understand the idea that the more people in any particular area that are immune to a particular illness - be it naturally or by vaccination - the less of that illness is going to be moving around in that population, which means smaller chance of infection for those who do not have the benefit of immunity (again, be it natural or from a vaccination).

But what I don't understand is why a couple years ago (or maybe it wasn't even that long?) when there were a few measles outbreaks here in the US, it seems like half the cases or so were in kids who had been vaccinated. And it was explained not as a failure of the vaccine but as a failure of the communities to reach a high enough percentage for herd immunity.

I don't get this. I just don't.

Either the vaccines are giving our children (and ourselves) immunity or they aren't. Because even if we are at 99.9% vaccination rates, what happens when one sick kid comes into the population? Can he spread to our children or not? Are my kids protected or aren't they?

I don't personally know anyone whose vaccinated kids got measles but I do know of a few people in my neighborhood who had their kids vaccinated for chicken pox and their kids got chicken pox anyhow when there were a few cases going around (this is 4-5 yrs ago).

So again, it's great if everyone is vaccinated and no viruses or illnesses around but unfortunately we don't live in a bubble. There are always going to be some unvaccinated for medical reasons or maybe religious reasons (I'm guessing christian scientists probably don't vax?) and plus people travel and bring things in (I guess less so now with so many travel bans). And if the vaccinated kids can pick up measles and chicken pox and maybe other stuff too from a sick kid.... well, what was the point then? It doesn't seem like only the unvaccinated kids suffer and the vaccinated kids are protected.

Please don't link me to articles and statistics. I wasn't kidding in my thread title. Explain it to me in the must simple, idiot-proof way. I really don't have a head for statistics or have much of a science background. I do want to finally understand this.

amother

Pearl

Tue, Feb 23 2021, 8:36 pm

I'll leave the complete answering to the more scientific types, but as I understand it vaccines are supposed to stimulate an immune response in the individual so that if they are exposed to that particular agent their body will quickly recognize it and produce antibodies that will fight it off. Not everyone reacts the same to every vaccine.

For example, I am in my 40s. I never got chicken pox as a child even though I was exposed numerous times. When I was a teenager I had to get the vaccine. Years later I had to get my titers checked and I didn't have any so I had to get the chicken pox vaccine again due to my job. If that had been the MMR vaccine, then I would have been vulnerable to measles because my body wouldn't have developed enough antibodies to fight it.

amother

Burgundy

Tue, Feb 23 2021, 8:46 pm

You raise a few good questions.
1:Let’s say herd immunity is when 98% of population is immune to a specific virus (don’t know exact numbers, just make believe) then it is harder for the virus to spread because it needs to reach those 2% of people that aren’t immune. If the virus doesn’t have whom to go to, then the outbreak is over.
2:When talking about the measles outbreak, there were a few reasons why it spread even among vaccinated people; first, you need 2 mmr shots for it to be effective and not all kids got the 2nd dose already, second, babies under a yr don’t get the vaccine yet, but are able to catch and spread measles, third, even with 2 mmr vaccines, it is still not 100% effective. Some people lose their immunity sooner than others.
Basically, the goal is to get as many people as possible to be immune so that the virus has a harder time “catching people” and having them spread it.