Effect Of Not Vaccinating?

[sanctus]

Premise 1: there are plenty of threads and one active speaking about pros  and "cons"(?) of vaccinations, this is not the topic of this thread

 

Premise 2: just in case someone over interprets my question, I am very anti-anti-vaccinationations (--> hence pro-vaccination, but see premise 1).

 

 

When people criticise the anti-vaccination movements one of the arguments is that you endanger the society you are living in. Since all the other arguments where convincing I just took this one for granted (I admit I did not analyze it and even used it), but thinking about it I do not understand how it works.

Take a small society, say a village of 100 people if 99 are vaccinated against X and 1 is not. How does this one person endanger the village if he/she gets disease X? Because the other 99 are already immune thanks to the vaccination.

 

Or does this argument go in the way that this one person endangers all the newborns not yet vaccinated?

 

[Buffy]

This scenario is the extreme example of what herd immunity is all about: that if ONLY ONE person in a 100 person village is not vaccinated, the chances of them transmitting or contracting it is ZERO. As you increase the percentage, the probability that a disease will be transmitted stays low, because the carrier has to come in direct contact with the low number of other unvaccinated people in order for them to get it. If a very HIGH number of people are not vaccinated--even if it is far less than the majority--then the probability that someone will get it increases because the number of paths through the population with additional carriers being infected increases dramatically.

 

If I have time this weekend I'll put up the numbers in more detail, but those are the basic principles.

 

In the real world beyond the pure math that drives it is that as a practical matter, some subset of the population is going to be allergic to the vaccine, and as a result MUST not take it for medical reasons. If EVERYONE else takes the vaccine, chances improve dramatically for those who cannot take it that they will remain uninfected.

 

The problem is that it's gotten really bad: vaccination rates for the county I live in (which is actually extremely conservative and is the home of Disneyland where the big outbreak of measles occurred last year: this problem knows no ideological bounds) among Elementary school children (5-12 years) fell to 60% last year. The state passed a law this year eliminating "personal belief" exemptions so we're hoping the vaccination rates will begin to rise soon.

 

 

The best lightning rod for your protection is your own spine, :phones:

Buffy

[pgrmdave]

https://www.washingtonpost.com/posteverything/wp/2015/02/03/why-a-few-unvaccinated-children-are-an-even-bigger-threat-than-you-think/

 

So, how do we calculate what fraction of a population needs to be immune to reach herd immunity? First, we need to know what the reproduction number, or R, is. That’s how many new cases a single case of an infection will cause.

 

Imagine that you are infected in a completely susceptible population, and you pass on the infection to five other people (ieR=5). In order to prevent an outbreak, at least four out of those five people, or 80 percent of the population in general, should be immune. Put differently, 20 percent of the population may remain individually susceptible, but the population would still remain protected.

 

So if you can estimate the reproduction number for a given disease, you can calculate the fraction of the population that needs to be immune in order to attain herd immunity.

 

For influenza and Ebola, the number R is about two. For polio and smallpox, it is around five to eight. But for measles it is much higher, somewhere between 10 and 20. And because of that, the goal for measles vaccination coverage is typically around 90 percent to 95 percent of a population.

The thing to remember is that vaccines are neither 100% effective nor 100% long-lasting, so if you need 80% of the population covered for good herd immunity then you need more than 80% of the population to receive the vaccine.

[Turtle]

What Would Happen If We Stopped Vaccinations? @ CDC

[bolding mine]

 

...

A final example: what could happen.

 

We know that a disease that is apparently under control can suddenly return, because we have seen it happen, in countries like Japan, Australia, and Sweden. Here is an example from Japan. In 1974, about 80% of Japanese children were getting pertussis (whooping cough) vaccine. That year there were only 393 cases of whooping cough in the entire country, and not a single pertussis-related death. Then immunization rates began to drop, until only about 10% of children were being vaccinated. In 1979, more than 13,000 people got whooping cough and 41 died. When routine vaccination was resumed, the disease numbers dropped again.

The chances of your child getting a case of measles or chickenpox or whooping cough might be quite low today. But vaccinations are not just for protecting ourselves, and are not just for today. They also protect the people around us (some of whom may be unable to get certain vaccines, or might have failed to respond to a vaccine, or might be susceptible for other reasons). And they also protect our children’s children and their children by keeping diseases that we have almost defeated from making a comeback. What would happen if we stopped vaccinations? We could soon find ourselves battling epidemics of diseases we thought we had conquered decades ago.

[billvon]

Take a small society, say a village of 100 people if 99 are vaccinated against X and 1 is not. How does this one person endanger the village if he/she gets disease X? Because the other 99 are already immune thanks to the vaccination.

 

There are some problems with your assumption.

 

1) In your village of 100, 3 or 4 of the people there will not have vaccinations because they cannot handle them; they are immune-compromised or have other issues which makes taking the vaccine dangerous for them.

 

2) In your village of 100, a few will be vaccinated but it will not "take" - vaccinations are not 100% effective.

 

3) In your village of 100, that 1 person won't stay 1 person for long.  "If Joe doesn't have to get his kids vaccinated, why do I?  It's still a tiny percentage."  And soon half the village is unvaccinated.

 

4) Even as vaccination rates decline, diseases do not return immediately.  Thus the village may go for years before polio strikes.  And at that point it's too late to vaccinate everyone.  If, at that point, 70% of the village is not vaccinated, you might see 10% of the unvaccinated people dead and 10% of them paralyzed.  And many of them will not be the people who skipped vaccines, but will be the people who could not get the vaccine for medical reasons, or the people who got the vaccine but did not become immune.

 

For every disease there is a herd immunity threshold.  It varies by disease.  For polio it's ~83%, for measles it's ~93%, for smallpox it's ~84%.  That means almost everyone in the community has to be vaccinated, so that even when you account for the non-immune vaccinated and the immunocompromised, you can keep immune rates above 93% (or whatever the threshold is for that disease.)  If you can do that then the disease basically never spreads; if one person catches it, they don't spread it.

 

(Interestingly the herd immunity threshold for the flu is closer to 40% - which means even moderate vaccination rates are very helpful in preventing spread of influenza.)