I believe conditional acceptances are not official until some/all of the following are met (according to each school):
- All LORs are received.
- Final grades/transcripts received.
- Background check is clear.
- Immunization records up-to-date.
- Physical examination clear.
- Deposit mailed.
- (Etc.)
Each school should tell you what they require, but the list I mentioned seems to be pretty standard.