What Is Immune Amnesia? This Measles After-Effect Reduces Your Immunity To Other Infections

Measles dominated health headlines last year — the U.S. experienced a record-breaking number of measles cases, children died, and the strain of managing outbreaks in communities fell hard on the shoulders of parents. According to the U.S. Centers for Disease Control and Prevention (CDC), the nation is already set to outpace last year’s numbers. As more and more Americans contract measles, the complications of the infection will become more common, too. And there’s one complication that impacts everyone who gets the measles: immune amnesia. So what is immune amnesia, and how long does it last?

Measles is often referred to as a respiratory virus because it is transmitted via small droplets in the air. You can breathe it in after walking into a room where an infected person was up to two hours prior. But when the virus infects the body, it doesn’t target our respiratory system.

“The virus predominantly infects cells of the immune system; the cells of the immune system are best known to most people as the white blood cells,” says Dr. Rik de Swart, a virologist at Erasmus MC, University Medical Center Rotterdam in the Netherlands. Through their research, de Swart and colleagues have learned that memory cells — a specific type of white blood cell — are the measles virus’s primary target.

We all know our immune system learns to fight off viruses after it has been infected with them once before; memory cells make that possible. After you’ve experienced an illness and recovered from it, memory cells learn to make antibodies to combat it and are then prepared to fight that virus the next time you’re infected, de Swart explained. The measles virus attacks these cells, rendering them unable to produce antibodies that would fight off infections it “remembers” from past exposures.

Experts call this immune amnesia.

You may have heard of some rarer complications from measles infection: encephalitis, pneumonia, subacute sclerosing panencephalitis (SSPE), and even death. In the U.S. and Europe, de Swart says 80% to 90% of people with measles recover with no long-term complications. But immune amnesia affects every person infected with measles to some extent, he said. Research suggests immune amensia can wipe up to 73% of your immune system’s memory.

“Measles is one of those diseases that you experience only once in your life, and most vaccinated people will never experience it. But if you get measles, you will always get some degree of immune amnesia. Whether or not that is clinically relevant will differ very much between different patients,” he said.

Researchers haven’t yet pinned down precisely how long immune amnesia lasts. Based on epidemiological studies, the potential maximum duration of immune amnesia is up to three years, but de Swart emphasized that would be a very extreme case. For many people, he says, “the major impact of measles immune suppression is in the first weeks to months after you have the disease.”

The big question being researched now is whether the immune system eventually “remembers” the infections it once knew how to fight, or if the person has to endure all those illnesses again like it’s the first time. The American Academy of Pediatrics asserts that new infections and vaccines are the only way to get the immune system’s memory back.

“It is possible that the system would recover by itself, but it's not unlikely that for many of these infections, we do indeed need re-exposures to get the system back on track,” de Swart agreed.

In 2025, the CDC logged 2,267 confirmed measles cases nationwide, and already there have been 588 confirmed cases in 2026. These are massive leaps from the 59 cases in 2023 or 285 in 2024. Ninety-four percent of infections happened to people who were unvaccinated or whose vaccination status was unknown. Surges in measles cases are often the “canary in the coal mine” that vaccination rates are declining overall, de Swart said, and can signal more vaccine-preventable illness outbreaks to come.

“Of all the infectious diseases that we know in humans, measles is considered the most infectious one, the most contagious virus. If you have weaknesses in vaccination programs, measles is almost always the first disease to pop up. It will always find those pockets of people that are unvaccinated at some point, either because the unvaccinated people themselves are traveling or because people who have been traveling bring the virus into the community. But it's always measles that you see first, and then other infections follow later.”

To keep measles out of the community, 90% to 95% of people need to be vaccinated against it, and across the U.S. and Europe, more people are choosing not to vaccinate their children, said de Swart. The AAP recommends the first dose of the MMR vaccine be given between 12 and 15 months of age, and a second between 4 and 6 years of age. Roughly 95 out of every 100 people will be protected from measles infection after getting their first dose of the MMR vaccine, and two doses of MMR protect 97 to 99 of every 100 people, the AAP says. The organization emphasizes that vaccination is a far safer way to provide immunity than by letting them get a measles infection.

“This is really not a harmless childhood disease,” de Swart said. “This is really a virus that can do incredible damage to a child's immune system.”