Does an influenza vaccine interact with other medications?

The effect of influenza vaccines on other medications is very small. The metabolism of phenytoin, theophylline and warfarin may be slightly affected by an influenza vaccine. Despite these effects, there are no known harmful drug interactions that occur with influenza vaccines. People with weak immune systems, including those who take medications that weaken or suppress the immune system, such as corticosteroids, may not obtain the same degree of immunity to the flu virus as healthy people.