Serious. These medicines may interact and cause very harmful effects. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
Methotrexate, depending upon your dose, may suppresses the immune system preventing your body from responding correctly to the vaccine.
What might happen:
If you are receiving methotrexate, you may not develop disease immunity from the vaccination.If you are taking a high dose of methotrexate, a live vaccine may cause you to develop the illness it was supposed to prevent.Note that the inactive type of vaccines cannot cause you to develop the illness it was supposed to prevent, even if you receive a high dose of methotrexate.
What you should do about this interaction:
Before receiving a vaccination with a live vaccine, let your doctor know all of the other medicines you are taking, especially if you take methotrexate or other medications that work by suppressing the immune system (e.g. some medicines for rheumatoid arthritis or inflammatory bowel disease) or if you have recently received radiation or chemotherapy for cancer. Your doctor may decide to give you an inactive vaccine, or may want to change the timing of your vaccination.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.Reference:1.Centers for Disease Control and Prevention. General Recommendations on Immunization. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR January 28, 2011;60(RR No.2):1-64.