I’ve often heard and read that unvaccinated individuals put others (presumably vaccinated) at risk. How does this happen exactly? Is it just that vaccines aren’t 100% effective and having an unvaccinated person contract the disease makes it more likely to spread amongst everyone else?
I’m in the midst of debating an anti-vacciner and would prefer some reputable sources. Thanks! 
Several reasons, including:
Many vaccines don’t last forever. We don’t know, for example, if people vaccinated against smallpox are still good to go or not. If you go carrying it into that population, we’ll find out.
Some people can’t be vaccinated - little babies, people with immune problems, etc. That population needs to be kept as small as possible so those people don’t come into contact with a disease that could kill them through no fault of their own (or of their parents.)
Here is one story with a link to actual research into the phenomenon.
Vaccinations don’t just protect one person. Epidemics happen because disease become very common in a particular population, that makes it possible for the disease vector, virus in most cases to infect people more quickly, which again increases the number of new sources of the disease. First two people have it, then 8, then 50, then 200, then 4000.
But when the majority of a population is given this immunity, the vectors have a much smaller chance of infecting others. So, sixty patients become 62, then 60, then 55, then 20, then 2, then 0. So, if you are the only person in a city who doesn’t get vaccinated it is likely that the only person who is at risk is you. (You can still be infected by an animal in some cases.) But if you also neglect to have your kids vaccinated, and your church group follows your advice, you have all be a part of the increase in risk.
Tris
There is a phenomenom called herd immunity, which is much as Triskadecamus describes.
Good luck with that - my experience is that the anti-vax crowd tends to dismiss out of hand anything that contradicts their notions.
Regards,
Shodan
One very important thing to note from this cite:
Not all people who receive a vaccine will become immune to the disease. These people depend on herd immunity to protect them.
Not all vaccines ‘take’ so some percentage people don’t mount enough of an immune response to the bug.
People will lose their immune response with time. Elderly people will often suffer a decreased immune response, which is part of why shingles increases with age - they can no longer keep the virus contained. Even healthy robust people can have a decreased immunity with time - you need a booster for tetanus, for instance.
Not everyone can get a vaccine. People with egg allergies can’t get flu vaccines. People with compromised immune systems (transplants, as well as other things) can’t get live vaccines. These people are counting on the rest of us to keep them alive by blocking the disease’s path to them with immune people.
Then mention that Jenny McCarthy son doesn’t, and didn’t, have autism, which was not caused by vaccines, and that Jenny says so (http://www.hollywoodlife.com/2010/02/26/jenny-mccarthy-says-her-son-evan-never-had-autism/)
It is very rare for vaccines to hurt someone. Not impossible, but very rare. It is not rare for the diseases that vaccines stop to hurt someone. Research some of the diseases for which we vaccinate, and the choice becomes pretty straightforward. Measles has a fatality rate of 3 / 1000 healthy people in the west.
I might also point out that we don’t vaccinate for diseases where the vaccine can be dangerous. You don’t get rabies vaccine when you’re a kid, because the vaccine has a high rate of significant side effects. You get it when you get bitten by a bat, because rabies will kill you dead. So it’s not like the concept of dangerous vaccines is unknown and unappreciated. It’s simply that the benefit for standard vaccination is huge, and the risk is very very low.
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There are quite a lot of people who are advised not to get some live vaccines because this group includes those with asthma and autoimmune diseases (in my family alone that’s Crohns Disease and Psoriasis, so you can see how common these diseases are - here’s a long list of them) too. If we’re lucky, as we were in the case of the H1N1 vaccine, they can make a dead virus version too.
Modern vaccines have kept us from being exposed to formerly common diseases, which either killed us or rendered us immune. As a result, without modern vaccines, we would be as unprotected as the indigenous populations of the Americas when Columbus arrived.
It is estimated that as high as 90% of the 1492 population died of diseases they had never encountered - like measles and smallpox. Not something any population should have to experience.
IMHO, the two greatest misuses of modern medicine are to ignore vaccines and to overuse antibiotics - both in the food industry and in the ‘Doc, give me an antibiotic for my cold.’.
This is an anecdote, but it illustrates what the good folks have said above. I had a rubella shot as a child. When I got pregnant with my first, they did the prenatal bloodwork and I was negative for immunity to rubella. So when my first was born, I got another shot. (You can’t have the shot while pregnant - it can cause the same birth defects that the disease can, per the OB.)
Three years later, I’m pregnant again and the same thing - no immunity. I got another shot after the second was born. A year after that, pregnancy number three and still no immunity. That’s three shots. I gave up. If three didn’t do it, four isn’t likely to.
I went through three pregnancies either without immunity or somehow showing a false negative. I have to assume no immunity. I’m just glad that I didn’t meet anyone with rubella during that time.
The key problem is “herd immunity” as mentioned above.
The first epidemic of black death about 1350 was estimated to have wiped out about 1/3 of Europe (Barbara Tuchman, A Distant Mirror) It then disappeared as the survivors were immune. It returned several generations later, when many of the immune individuals had died; and continued to reappear in waves when conditions warranted. So too did other diseases like smallpox or polio.
Basically, an epidemic happens if it is easy to infect people you come in contact with. Flu, smallpox, bubonic plague, and other transmissible diseases where infections are airborne (sneezes, etc.) rely on human contact to pass them on. The more people you meet that are not immune, the more likely some of them will catch it and so pass it on too.
Obviously vaccines break this cycle by reducing the candidates for infection. Skipping vaccinations is analgous to skipping a lineup. If everyone lines up except you, you break into the front of the line and wow, that’s great; all the benefit and none of the expense. Too many people do it, there’s no line just chaos.
Same with vaccines; as long as everyone you meet is vaccinated, you very likely won’t get the disease; from humans, at least; if you work with birds or swine, you might get the flu from them… So where’s the safe point? 1%? 5%? 10%? 50%? How do you ensure you don’t go over the critical threshhold? Like lining up, the only way to ensure it’s fair is if everyone does it unless they really physically can’t. As mentioned, there’s always the risk we have a small non-immune population anyway due to vaccine failures and the quirkiness of the human body.
… which is no freaking joke. I know a deaf guy who’s deaf because his mother caught it while pregnant.
By serving as incubators for new and exciting versions of the bug. If a flu bug comes near me, my body immediately recognizes it and launches an attack, because it has been educated by the vaccine in how to recognize these proteins.
If an unvaccinated person gets the bug, it not only gets to take hold while their immune system takes time to recognize and ramp up, but also gets to reproduce in a new environment, which may include any number of variables (not least of which is the patients own DNA) which it has not encountered before. In the process it can lose/gain attributes which make it easier/harder for the next person to catch or fight.
It may even change just enough that my immune system no longer recognizes it, and succumbs despite my vigilance.