I drank one of the vials to get the achievement and now I can't bite anyone. I would like to be able to bite again so I can go for that achievement. Does anyone know how long it'll take for the effect to go away?

i believe it was about a week? i forgot exactly, sorry. if im not mistaken, there is a cure.. the one in Louis' shop, from the earliest year you can see?
better check with subetalodge as well? this makes me wonder if we can redeem the skins from those infections, lol, but i guess not.

The cure doesn't work on 2014 viruses

Also, you cannot redeem these in the wardrobe.

Does that mean I have no way to get rid of this infection from the vial, I just have to wait it out?

Yeah, you have to wait for it to cure on its own, like last year

Darn, I guess that means I won't be able to get the bite achievement.

Thanks for the information though, I really appreciate you taking the time to answer my questions. ^-^

you can bite others with the vial infection once it progressed to the final stage.