Overheard in the grocery story checkout line

On my way home from work today, I found myself at the grocery store that is affiliated with the chain at which we shop the most but that is the slowest of the three stores I go to most often when it comes to getting checked out. So, I had a long time to stand in the checkout line at 5:55 this evening. The lines were ten people deep. The woman in front of me had a blue tooth phone in her ear. I overheard her saying something to the effect of "they tried to give my sister's boy the flu shot, but why should he get it. It is just like giving him the virus. Why not just wait and see?" Using a killed virus, it is not just like "giving the child the virus". I thought that the press in general has done a good job of trying to convince people that the flu shot will not give them the flu.

Why is this economics rather than just an interesting observation of human nature to believe what we want to believe rather than information that is put forward? It is an economic question because you could ask "Why did not you try to set here straight? You are a public health economist after all.

That is an interesting question. If the disease were not a contagious disease, what she or her sister chooses to believe and chooses to do would not affect me. However, since we are discussing an infectious disease, her actions and her sisters actions and how these actions affect their kids has the potential to affect my kids or me. We call this an externality.
Why was I not concerned enough about the externality to "set her straight". First, I could perceive that the cost associated with this particular person not getting her son a flu shot would have a limited chance of affecting me. Why? Unless I shop at that grocery store again in the near future (and after the 10 deep checkout line I do not expect to do so), I probably won't come across her and I have the preconceived notion that my kids won't come across hers or her sister's?

Second, I could perceive that even if I do cross paths with the woman, her sister, or their kids I am not likely to be affected. I've had a few bad colds but never really the flu. I am generally healthy. Haven’t had anything yet this fall. So, perhaps I just think there is no need to worry.

Third, I could perceive that even if I change one person's behavior there are so many others out their whose behavior I will not change that one person's behavior change will make little difference in population level outcomes.

Finally, I may perceive the cost of changing a person's behavior to be too high. In other words, even if I could see a tangible potential benefit for myself, the effort it would take from me to help her change her behavior was "too much" to be worth it or at least more than the value of possible prevention.

So, while the decision not to vaccinate that I heard being discussed was not necessarily economically rational (given the misinformation), my decision not to do anything could be considered rational and could suggest how I view the world working. And, just for the sake of argument, even with all the right information about the vaccine, choosing not to get one still could be an economically rational choice.