For Most Adults, One MMR Shot Is Considered Enough

Vaccination is the best way to protect yourself against measles, and for most adults a single shot of the MMR vaccine is considered enough protection, NPR reports. The guidance carries a qualification: there are certain situations that call for a second dose.

So the useful question for an adult isn't "one or two?" in the abstract. It's whether you fall into one of the cases where a second dose is called for. The default for most people is one shot, and the exception is situational rather than universal.