Important things to know about the human rabies vaccine?

June 28, 2023 9:21 AM

I was vaccinated against rabies in the mid 2010s. I recall at the time hearing something important about it, something along the lines of - if you've had a rabies vaccine that has since worn off, and you get rabies, your rabies won't show up on a test. It wasn't that exactly, I don't think, but something similar, and of course I can't find it now because search engines are terrible.
posted by wheatlets to Health & Fitness (7 answers total)

Here’s what the CDC has to say about it (previously vaccinated individuals)

https://www.cdc.gov/rabies/medical_care/vaccine.html
posted by raccoon409 at 9:42 AM on June 28, 2023

(For what it’s worth the human rabies vaccine only lasts about 3 years so I think if you were exposed you’d be treated as a non vaccinated individual).
posted by raccoon409 at 9:44 AM on June 28, 2023

Also I believe you have to get post-exposure prophylaxis regardless of vax status. It's just that you get a shorter series if you've been vaccinated within the effective period. So in some sense it doesn't matter, because it doesn't affect initial treatment at all.
posted by praemunire at 10:01 AM on June 28, 2023 [3 favorites]

Response by poster: I should clarify, it was definitely a bad thing. It wasn't "You may need less treatment if you were vaccinated previously", it was something that made me go "Oh shit, I am so glad I learned this, it's very important for doctors to know that I was vaccinated because otherwise I may not get proper treatment if exposed".
posted by wheatlets at 10:05 AM on June 28, 2023

Nothing bad that I'm aware of is associated with rabies vaccine. They don't test for rabies. If you've been potentially exposed (like from a bat or other animal interaction) treatment is initiated as described above. Maybe it was just a warning that protection will fade over time?
posted by emd3737 at 10:15 AM on June 28, 2023 [2 favorites]

Probably the right explanation if I understand the concern:

There are different kinds of antibodies your bodies make. It makes IgM very quickly for short term use and after a few weeks makes IgG for long term use.

If you are vaccinated for something, your body starts making IgG a few weeks later. If you get the infection of the same thing, it makes IgG a few weeks later.

Thus, I suspect the concern is that an assay for Rabies IgG wouldn't be able to differentiate between post-vaccination IgG and post-infection IgG.

However, because it takes weeks to make IgG and you may have clinical symptoms before the human body has made IgG, you don't always exclude an infection based on the absence of a positive IgG.

I would not worry.
posted by chiquitita at 4:50 AM on June 29, 2023 [2 favorites]

Agree with chiquitita.

Good parts about rabies vax: if current (ie you've had yearly titres as many vets do), you get fewer post-exposure shots.

Bad parts: none.
Though if you were vaccinated that long ago and haven't pulled a titre before exposure, it's most likely you'll be treated as unvaccinated. Though I bet you're still less likely to die if exposed even that long after the original series.

If you haven't been exposed and were vaxxed that long ago, pull a titre to provide peace of mind, especially if you're considering travel to a rabies-endemic area. You may be surprised!
posted by esoteric things at 8:29 PM on July 3, 2023