Welcome to Ask The Doctor. We are here for your help.
Tetanus vaccine has no relation in making your birth control a failure. Tetanus is not considered as antibiotic.
If you are on birth control, then tetanus is not going to effect it any way and getting you pregnant. However, in case even if you get pregnant, tetanus vaccine has no relationship with it. In fact, to bring it best to your knowledge, any birth control method doesn't give you 100% guarantee of birth control.
In case you miss your periods, get a urine pregnancy test done after 10 days of missing the periods for the conformation of pregnancy.
See your doctor and share my opinion with him/her.
I hope it helps.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.