Why are non-vaccinated people a danger to public health?
February 4, 2015 8:23 AM   Subscribe

In theory, if most of the public is vaccinated against measles, only other non-vaccinated people are put at risk by non-vaccinated people who get the measles (or other vaccine-preventable diseases). But apparently some vaccinated people are also at risk? Is this really the case? If so, how common/easy is it for vaccinated people to get the disease that they were vaccinated against, and how does this happen?
posted by Mechitar to Health & Fitness (29 answers total) 9 users marked this as a favorite
 
Wired has an article about this that's pretty understandable. It's mostly a numbers game. And the big deal is people who can't get vaccinated because they are immunocompromised or for other reasons. They benefit from herd immunity without being able to contribute to it. And they are very vulnerable.
posted by jessamyn at 8:26 AM on February 4, 2015 [40 favorites]


Herd immunity. Wikipedia, Washington Post.
posted by Bentobox Humperdinck at 8:26 AM on February 4, 2015 [3 favorites]


This video gets into it a bit, particularly myth #3.
posted by ThePinkSuperhero at 8:35 AM on February 4, 2015


We need herd immunity to protect infants who often cannot be vaccinated until they reach a certain age and for people who have compromised immune systems (cancer patients undergoing chemo for example).

Those extremely vulnerable people rely on other people in the community to do the right thing in order to save their lives.
posted by brookeb at 8:39 AM on February 4, 2015 [17 favorites]


As the Wired article states, sometimes the MMR vaccine doesn't result in immunity. This is an issue for pregnant women, because diseases like rubella can cause miscarriage. So, for example, I am currently pregnant and I was tested early on to check my immunity to rubella. Apparently I'm one of those folks for whom the vaccine didn't take, so I have to hope that we don't have a sudden rubella epidemic, or else my baby could be at risk.
posted by cabingirl at 8:41 AM on February 4, 2015 [14 favorites]


The issues with whooping cough/pertussis and the effectiveness of its vaccine may be of interest: article.
posted by gudrun at 8:47 AM on February 4, 2015


It's all in the numbers.

If 30 people in a group are vaccinated and 2 people who choose not to be, then herd immunity will help protect those two, plus reduce the chances of one of the vaccinated 30 catching something anyway (see the current measles outbreak: the vaccinations reduce the likelihood of an immunized person getting measles, but doesn't 100% eliminate it).

The problem is, there are people, for instance infants who have not yet gotten vaccinated or individuals who --- per their doctors --- shouldn't be because of pre-existing medical conditions. So, that vaccinated-to-unvaccinated number is skewed even more, and that's where the trouble lies: you've got even fewer vaccinated people protecting the unvaccinated.

Think of the vaccinated as a wall around the unvaccinated: if there's a good strong, tall & solid stone wall around the unvaccinated, they're far more protected from attack by wild animals --- whoops, make that viruses and pathogens! --- than they would be if their wall was a short, weak picket fence.
posted by easily confused at 8:50 AM on February 4, 2015 [3 favorites]


Right, a lot of vaccines aren't 100% effective, So if you get exposed directly to a disease, there's still a chance you might catch it. But if a person is unvaccinated, but if they're exposed to a disease, they've got a good chance of catching it, and exposing anyone else they're in contact with. So basically, if you're exposed to an unvaccinated person, you are also essentially exposed to every person they've come in contact with, and if one of those people is unvaccinated, everyone that person has come in contact with... and so on. That's why people are angry about folks who don't get vaccines - they're involuntarily exposing anyone they come in contact with to each other, essentially.

Now that is an oversimplification, everything in real life is a percent chance, but with a few hundred million people in the country, you don't need very high percentages to get a lot of people sick.
posted by Zalzidrax at 8:51 AM on February 4, 2015 [3 favorites]


Yes, herd immunity.

Since you're asking specifically about those who have already been vaccinated, immunity can wear off (sorry for no link; google "vaccination wear off"). Additionally, most vaccines have limited success rates, so it's possible to be vaccinated and remain vulnerable without even knowing (another reason for herd immunity).
posted by whoiam at 8:52 AM on February 4, 2015


Unfortunately, "immune" isn't a binary condition. So another issue is that the strength of your immunity for many vaccines declines over time as the years go by since you've had it, with different durations for different vaccines and individuals. So you can be vaccinated, mount an immune response, but then be (incrementally) more susceptible to the disease over time as you get older. (Citation.)

This is related to one area where there's a grain of truth inside a nugget of bullshit from certain anti-vaxxers who claim getting exposed to disease is "better" for the immune system. Folks immunized by vaccines often have a less persistent immune response than people who got the fullblown disease - after several decades, they won't mount titers quite as high as folks who actually got sick instead of getting the shot. But from a risk standpoint, it makes a lot more sense to get vaccinated and get a booster shot down the road than risk the disease complications in the hope of a slightly stronger immunity via infection decades and decades later.

[Edit] Takeaway: another part of the numbers game is that even vaccinated individuals can become more susceptible eventually, even if the vaccine worked for them.
posted by deludingmyself at 8:57 AM on February 4, 2015 [7 favorites]


It goes so far beyond herd immunity and variable efficacy, even though those are the principal (correct) answers to your question.

To give you a bit more detail about what I mean, keep this in mind. Vaccines are a class of therapeutic drugs that are referred to as biologics--to put it simply, they're given this name because they're made in biological systems (cells, eggs, horses, etc.).

By comparison, a 'small molecule' drug is fundamentally just a chemical of some sort, a single molecule that doesn't vary over time. Production processes are standardized and always pump out the same final product. This is why it's easy for a manufacturer to come up with a 'generic' version of a drug--you just do what the other people did, show that it's the same chemical, and boom, market it.

A biologic is never 100% standardized, even by the same manufacturer. Every batch varies in some way, even batches made by the same manufacturer over time using the same recipe. Production processes can be controlled, but there's always some margin of error: a few extra seconds at a particular incubation step, a degree cooler during a purification stage, a different manufacturer of another reagent, etc. And that's understood in the regulations. Some vaccines, for instance, have expressions of the accepted range of potency compared to a standard that say, paraphrashing, 'the final product must be at least 75% as potency and less than 150% as potent as this standard vaccine you're comparing it to." That kind of range of potential therapeutic effect is unacceptable for small molecule drugs, but just the price of admission for a biologic.

So keep that in mind--vaccines can be standardized, but the standardization itself is more in line with being consistent than being identical from batch to batch. Variability of the product is guaranteed, which compounds issues related to the efficacy and immunogenicity of vaccines and the immune systems which have to respond to them. And this is for vaccines whose antigens don't appreciably change over time. Ones that do, like the flu vaccine, well... this shit gets complex, quick.

(Signed, epidemiologist.)
posted by late afternoon dreaming hotel at 9:04 AM on February 4, 2015 [48 favorites]


It's similar to why we need public fire departments rather than private pay-if-you-want fire brigades.

Let's say you can't afford to pay for the fire brigade because you have cancer (and in the US, that's expensive).

All your neighbors buy fire protection: You only have to worry about your own house -- you make sure not to play with matches, etc. You don't have to worry about a neighbor's fire flashing over to your property, as they all have fire brigade protection.

Let's say you have one one neighbor who chooses to not pay (he's got a lot of fire extinguishers, and thinks his house is particularly strong, plus his favorite celebrity doesn't have fire brigade insurance): chances are, your house will still be fine and only that neighbor will have a fire and lose his house. The rest of your neighbors have fire protection, so any fire will be put out long before it reaches your house. Of course you could be right next to that neighbor's house, and still end up losing yours. But your risk of loss is low overall.

Now, assume half your neighborhood chooses not to pay: well, chances are a fire in one house will spread to the next, and before you know it, every non-fire-protected house is up in flames. Now your house has little to no chance of avoiding fire. You'd get fire brigade protection if you could, but you can't, because you have cancer. Now your house is on fire, because your neighbors didn't feel like paying for the fire brigade.

It's like that. Only instead of fire, it's measles, and instead of houses catching fire, it's people dying.

[by the way some places do have this system for fire departments]
posted by melissasaurus at 9:08 AM on February 4, 2015 [17 favorites]


Right, a lot of vaccines aren't 100% effective, So if you get exposed directly to a disease, there's still a chance you might catch it.

One of the best examples of this is the recent NHL mumps outbreak. Most of the players had not only been vaccinated, but recently gotten boosters when they played in the Olympics.
posted by cjorgensen at 9:14 AM on February 4, 2015 [4 favorites]


Immunity can be partial: it's not all or nothing. Vaccination also fails to produce immunity in very small numbers of people, and is not always 100% effective. Immunity can also wear off. You might not be protected by the vaccine later in life.

Some people cannot get vaccines because they are immuno-compromised or too young. Some people have the vaccine, but later become immuno-compromised.

But this mostly won't matter as long as everyone who can safely get the vaccine does: the "targets" would be too few and far between. They are protected by herd immunity. But that breaks down when too many people don't get vaccinated.
posted by spaltavian at 9:18 AM on February 4, 2015


Getting sick with a disease like chicken pox is not a 100% guarantee that you'll always be immune to it, either. There are people who have had chicken pox more than once. The problem seems to be something inherent to the immune system, not just a problem with our current vaccines.
posted by Anne Neville at 9:27 AM on February 4, 2015 [2 favorites]


Vaccination for measles in this day and age primarily protects infants and a few immunological compromised children who haven't been vaccinated is my undersanding. Without vaccination I've seen the number of complications as 1 in 100 (minor) and 1 in 1000 (encephalitis). I had measles as a kid and it was a mild simple childhood disease, just like the anti vaxxers say. My brother had a severe case though and I know a couple kids who were hospitalized.

A few other diseases like mumps (possible side effect of sterility in adolescent men) and rubella (can cause miscarriage and birth defects) affect more of the population than measles which is why I think measles is the poster child for "childhood diseases are natural!!" crowd.

If we could maintain high enough rates long enough to consider it eradicated we wouldn't need to keep vaccinating, it wouldn't exist in the population.
posted by fshgrl at 9:30 AM on February 4, 2015


This doesn't directly answer the question, but I found this chart and info from the CDC useful to really visualize the recent impact of unvaccinated individuals as far as Measles outbreaks. See the huge spike in 2014, plus the fact that we're barely a month into 2015 and there's already 102 cases reported, 92% of them from one outbreak center.
posted by Crystalinne at 10:21 AM on February 4, 2015


Here's a real life example: The varicella vaccine is given in two doses, a year apart. A week before he was due to get his second vaccine, my two year old son somehow got the chicken pox. (We think he was probably exposed on a return flight from Hawaii; given that he screamed for 4.5 hours of a six hour flight, he probably deserved it.) Because of his initial dose of the vaccine, his case was incredibly mild -- he had 14 pocks on his back, and 48 hours they were crusted over and that was that. But during that time, he spent two hours in the child care at my gym (it was freezing cold outside that day and so I had just changed his diaper and left him in his fleece footie jammies, and since the pocks were only on his back, I didn't see them until after we got home) along with several other children, some of whom were too young to have been vaccinated. Despite the fact that the vaccine "mostly worked" -- his case was SO much less serious than the pox I experienced as a child -- he could have passed it along to one of the infants in the child care facility, and that could have been incredibly serious.

Fortunately, he didn't. In fact, when I took him to the doctor to have the pox confirmed, they were unable to even culture any virus out of the pock fluid, his viral load was so low thanks to the vaccine. But it was possible. That doesn't mean the vaccine was useless, obviously, but it does illustrate how immunity isn't binary.
posted by KathrynT at 10:24 AM on February 4, 2015 [4 favorites]


In case you're interested, there's a vaccine megathread going on at /r/askscience right now. If you're not familiar with askscience, it is heavily moderated and all answers must be cited and are typically made by people with "flair" (i.e., have had their credentials verified by the mods). It's a new thread, so not many answers yet, but it would be a good place to pose your question if you want a cited answer from a legit source.
posted by melissasaurus at 10:35 AM on February 4, 2015 [2 favorites]


Measles isn't trivial for everybody.

I was a kid before the chicken pox vaccine was in wide use. I got chicken pox when I was four, and I still have scars. I think my chicken pox scars significantly contributed to the development of body image issues for me, body image issues that I still have (heck, I've got body image subscriptions). My daughter was vaccinated for chicken pox as soon as they would give her the vaccine, to spare her the experience of thinking she's unattractive because she has chicken pox scars.
posted by Anne Neville at 10:44 AM on February 4, 2015 [1 favorite]


Also as a virus travels among people, it is more likely to mutate. If it mutates too much, vaccines may no longer work for it. So it might start with only unvaccinated people catching it but if enough of them did, eventually it could spread to the vaccinated population too
posted by KateViolet at 11:02 AM on February 4, 2015 [2 favorites]


The mumps are certainly not trivial to a grown man...my Dad slept on the sofa for two weeks with an icebag on his crotch because he was far too swollen to risk jostling in the marital bed...and there were no subsequent siblings, either.
posted by cookie-k at 1:07 PM on February 4, 2015 [3 favorites]


I will add that, in addition to biologics not being completely standard and some of the other stuff said here, humans aren't completely standard. So one of the reasons you get different reactions to the vaccines is because you are putting them into different bodies.

In some cases, like genetic disorders, we have some idea that the body is different in some important way. In other cases, we don't. Even with genetic disorders, the mechanisms behind how this stuff works is often poorly understood, which means that we generally do not have the information we need to predict how a particular person or particular "class" of people (ethnic group, people with a specific disorder, etc) will react. This aspect is part of where anti-vaxxers are coming from with their protests.
posted by Michele in California at 1:13 PM on February 4, 2015


Lots of great answers and information up so far.

My .02 to add, that I haven't seen explicitly mentioned here, is that since measles was so rare in the US after the vaccine was developed it wasn't known that some people need 2 doses of the MMR to achieve immunity to measles until the earliest rumblings of the anti-vaxx movement in the 1980s.

Since 1985, the standard of care has been to get the MMR at age 1 and 5. However, there are plenty of adults around today who missed that second dose. The effectiveness rate for them is lower than the 98% rate for people with two doses.

Plus measles is just, super super contagious. A pinnacle of virus evolution.
posted by fontophilic at 1:17 PM on February 4, 2015


I'm one of those immune-compromised people. If you don't get your child vaccinated because it's trendy not to do so, and your sick child comes near me, I could die, even though I've been vaccinated for everything except shingles (live virus). For me, EVERY cold turns into bronchitis or pneumonia. The flu would likely kill me. The same kind of people who don't get their children vaccinated for "philosophical reasons" also think it's okay to bring sick children out in public.
posted by clarkstonian at 4:53 PM on February 4, 2015


>Why are non-vaccinated people a danger to public health?

I'll tell you why:

My son, then 11, was vaccinated against mumps. The vaccine is not always 100% effective. He went to school in Japan where MMR is not mandatory. There was a mumps outbreak. He caught the mumps. Luckily because he had the vaccine, he was off school for 3 days. However, he could not eat for 2 days and lost weight - a disaster at that age.

Had the other children been vaccinated, he would not have caught the mumps.

As well:

This past December my son's friend caught pertussis - whooping cough. He had been vaccinated, but the booster schedule was coming up and likely he has fewer antibodies to fight off pertussis.

If other children had *all* been vaccinated (at one time pertussis was almost wiped out) he would never have caught it.

He has been off of school for more than two months, and has experienced *a* *lot* of pain.

That is why we must vaccinate our children. For "herd immunity" and to eradicate these nasty diseases.
posted by Nevin at 12:42 AM on February 5, 2015 [1 favorite]


I just wanted to chime in to add that measles isn't trivial, and the complications it can lead to can be devastating.
posted by discopolo at 4:25 AM on February 5, 2015


The mumps made me completely deaf in one ear, and possibly sterile. Not a trivial disease either.
posted by Halloween Jack at 12:52 PM on February 5, 2015


Watch this.
posted by John Cohen at 10:13 PM on February 5, 2015


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