How long does immunity from MMR vaccines last?

In a CBS news interview, HHS Secretary RFK Jr. claims that immunity from the MMR vaccine wanes quickly in order to explain why the measles outbreaks are spreading farther and longer than they might otherwise.

The claim that the MMR wanes quickly is untrue. Even if the antibodies your body makes from the vaccines lessen over time, your immune system still remembers the virus using special memory cells. These memory cells usually remain in your body for your entire life, able to respond quickly and protect you from measles if you’re ever exposed.

Also, measles is so contagious that if a person susceptible to measles walks into a room where someone with measles had been two hours prior and left, 90% of those people would still get measles. Before the vaccine was available, nearly everyone got measles.

If the measles vaccine were waning quickly, as Kennedy claims, leaving a large number of people susceptible, we would see a huge number of vaccinated people getting measles. But that’s not what we are seeing. Of 561 cases identified, 550 of them are unvaccinated, while only 11 have had only one or two vaccine doses. We know that one dose of MMR protects up to 93% of people while two doses protect up to 97% of people, and these numbers track what we’d expect if the vaccine was working as expected.