How do rabies shots work?

Question

I understand the basics of vaccines and I get the rabies vaccine works, but in the instance where you are attacked by a rabid animal and bitten, how does getting the vaccine immediately help with the development of the disease? Is it not already in your bloodstream?

In: Biology

Answer 1

You are correct that usually you need a vaccine *before* you are exposed to get much value out of it. Rabies is a bit of an exception to this.

Yes, a bite from a rabid animal will get rabies into your blood almost instantly. However, rabies doesn’t infect you through your blood, at least not directly. It travels through your nervous system and eventually enters your brain. Part of why it’s so deadly is that it’s able to cross what we call the blood-brain barrier. Almost nothing can do that, including medication and your own immune system. So once an infection is in your brain, it’s very very bad because, generally speaking, we don’t have any treatments for that and you don’t have an immune response either. You just die.

Rabies can sneak into the brain by traveling through your nervous system. The one break we have, is that this is a very slow process. Bloodborn pathogens will circulate through your entire body in a matter of minutes. If you get bit on the hand by a rabid dog it can take weeks or even months for the virus to make its way to your brain. That gives you plenty of time to go get the vaccine before the disease can infect your brain. As long as you get the immune response rolling *before* that, your body can clear it out and you’ll be fine.

If you wait, though, and don’t go to the doctor until you have symptoms, you’re dead. That’s too late for the vaccine because the virus is already in your brain. We don’t inoculate people ahead of time because it’s a painful and expensive shot that most people will never need it anyway. Plus you’d probably want a booster after a bite anyway and as I said there’s plenty of time to get it *after* a bite as long as people are educated about how to respond to an animal bite, which in America at least they generally are.