With record-breaking measles activity reported in the U.S. throughout 2025 and into early 2026, many adults are asking a critical question: Am I still protected by the shots I got decades ago?

The short answer is yes, almost certainly, but there are rare exceptions you should know about.

1. The Power of Two Doses

The current medical gold standard is the two-dose MMR (measles, mumps, and rubella) series.

97% Effective: Two doses are roughly 97% effective at preventing measles.
Lifelong Protection: For most people, this immunity is considered lifelong. Once your immune system is trained by these two doses, it typically remembers how to fight the virus for good.

2. Why Breakthrough Infections Happen

While rare, “breakthrough infections” do occur. In 2025, approximately 4% of U.S. measles cases occurred in fully vaccinated individuals. This can happen for a few reasons:

Primary Vaccine Failure: About 3 out of every 100 people don’t develop a strong enough immune response even after two doses.
Intense Exposure: In rare cases, being in very close, prolonged contact with an infected person (like in a household) can “overwhelm” even a vaccinated immune system.
Waning Immunity: Recent studies suggest that for a small number of people, antibody levels may decline slightly after 10–20 years.

3. The “Milder” Silver Lining

If you are vaccinated and still catch measles, the experience is usually vastly different from an unvaccinated case. Vaccinated individuals typically have:

Milder symptoms (often called “modified measles”).
Lower viral loads, making them much less likely to spread the virus to others.
Virtually zero risk of the most severe complications like permanent brain damage or death.

4. Check Your “Era”

Your protection level may depend on when you were born:

Born before 1957: You are likely immune because you probably had measles as a child before the vaccine existed.
Vaccinated 1963–1968: Some people in this window received a “killed” version of the vaccine that was less effective. If this is you, the CDC recommends getting at least one dose of the modern live MMR vaccine.
Born before 1989: You might have only received one dose, as the second dose wasn’t standard until 1989. While one dose is 93% effective, a second dose is recommended for full protection.

What Should You Do Now?

If you’re unsure of your status, you don’t necessarily need a booster, but you have options. You can ask your doctor for a titer test (a blood test to check for antibodies) or simply get another MMR shot. Experts at Mayo Clinic and the CDC note that getting an extra dose is safe even if you are already immune.