Yesterday I was ready to talk about Herd Immunity, but thought maybe that was getting too deep into things. I could imagine everyone’s eyes glazing over. After I saw The Onion article that Dan linked, I thought that’s a good last word.
Then I read in the newspaper this morning how two politicians (Rand Paul and Chris Christy, both in the running for President in 2016) have spoken out on this issue. And I got really mad at them. How dare they try to play political football with this! I would love the chance to speak to them face-to-face on this, and say “ARE YOU OUT OF YOUR MIND?”
What is Herd Immunity? Of those who do get vaccinated, not everyone develops immunity. Nothing is 100% in biology. Some people have allergies or medical conditions that put them at risk, others have medical conditions that block developing an immune response, and others have religious reasons (such as Christian Scientists, Jehovas Witnesses or others) to avoid vaccination that are legitimate under US law. And as we’ve seen recently, some refuse vaccination for irrational reasons. Unfortunately California and some other states protect this last type of vaccine refusal.
Read more about herd immunity here:
http://en.wikipedia.org/wiki/Herd_immunity
To prevent the spread of contagious diseases, only a small fraction of the population (or herd) can be left unvaccinated. This is best reserved only for those who cannot safely receive vaccines, those who don’t have functioning immune systems, or those who have legitimate religious reasons.
Because the measles vaccine is not 100% effective, epidemiologists have tried to answer this question: If one person with measles enters a population that is not sick, what percent of that population has to be immunized to prevent spreading measles?
For measles, Herd Immunity is believed to kick in when 83-94% of the population is immunized (see the table on the Wikipedia link). If enough people choose to avoid vaccination for “personal belief” reasons, it can threaten herd immunity. We may have already gone below that threshold.