If the vaccine is related for travelling for business in some countries where there is a requirements, I am sure you should include it on your expenses, if there is not available Visa/Medical profilassis I would use "miscellaneous" or "Others".
If specific to Covid-19 vaccine, I would be surprise it is charged in your country, as I thought it was a free vaccine globally to take.
If my answer didn't provide you with an actual solution, please escalate within your HR or Expense department team.
@vivek I agree with @Munari_alEXPert that if you are referring to the COVID vaccine, it should be free. If for some reason you did have to pay, you should speak to your manager about whether it is something your company reimburses and if so, how to submit that.