Severe. These medicines may interact and cause very harmful effects and are usually not taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
Acyclovir, famciclovir or valacyclovir are a type of antiviral medicine that may inactivate varicella or zoster vaccines before your body can develop immunity to the virus.
What might happen:
The vaccine may not work as well if it is given within 24 hours of taking a dose of acyclovir, famciclovir or valacyclovir, or if you begin or restart acyclovir, famciclovir or valacyclovir within 2 weeks after receiving the varicella or zoster vaccine.
What you should do about this interaction:
Before receiving the varicella or zoster vaccine, make sure your healthcare professionals (e.g. doctor or pharmacist) know that acyclovir, famciclovir or valacyclovir have been prescribed for you. Your provider may want to delay giving the vaccine until after the medicine is out of your system. If you have received the varicella or zoster vaccine in the previous 2 weeks, let your healthcare provider know before you start acyclovir, famciclovir or valacyclovir.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.