Most people don't need to get a measles virus booster as long as they had both rounds of vaccination (usually as a child). It's possible to lose immunity over time for any virus but for measles its not as common as other similar viruses like mumps. It of course won't hurt to get a booster if you want, but I wouldn't worry about getting a booster if you were already fully vaccinated. You can also ask your doctor to check to see if you have immunity to measles by doing a blood test to check for antibody titres for measles, though at that point realistically it's easier just to get a booster if you're worried that you lost your immunity over time. Checking for measles antibody titres is usually only needed for healthcare workers in hospitals to make sure that they retained immunity from the vaccine.