This year, the United States has seen the biggest surge of measles in decades, resulting in nearly 1,500 confirmed cases across the country. Driven by low vaccination rates, these outbreaks are dangerous. On average, measles kills 3 out of every 1,000 infected people. But death isn’t the only risk. Measles survivors may develop a strange but serious side effect: immune amnesia.
You may have heard of amnesia before. It means memory loss. Meanwhile, the immune system is what protects your body against infections, helping you to stay healthy. Immune amnesia is just what it sounds like: your immune system forgets what the flu, common cold, and other viruses look like. This is a big problem.
The Immune System’s “Most Wanted” List
Your immune system isn’t a single organ. Instead, it’s a network of organs, cells, and glands. These body parts work together to fight off germs.
When you get sick, your immune system ‘takes a picture’ of the germ. These ‘pictures’ are preserved by a special type of immune cell called memory cells. This way, the immune system keeps a photo album of its “most wanted” criminals: the RSV you caught when you were five, the mono that kept you in bed for a month as a teenager, last year’s flu, and a few different versions of the common cold.
This photo album keeps your immune system on guard for years, ready to recognize old enemies the moment they show up again. Just like a “most wanted” list helps police to recognize and capture criminals, the immune system’s shared photo album helps its memory cells to recognize dangerous germs and destroy them. That way, the germ can’t get you sick a second time.
This is why you only get some diseases, like chicken pox, once. It’s also why vaccines work—they basically give your immune system a photo of a new germ. (You may be wondering why you can still catch the cold multiple times. That’s because there are actually many different viruses that cause cold symptoms. Each time you get sick, it might be caused by a different type of virus.)
This is also one reason why kids get sick more often than adults. Their immune systems are still learning to recognize the most common germs. Each time a kid gets sick, their body adds one more photo to the album. By the time you’re an adult, your photo album is pretty thick, and your body can recognize and fight off most germs.
So what happens when measles enters the picture?
A Hostage Situation
But measles has a superpower most germs don’t. It can wipe clean the immune system’s photo album, erasing years of protection in a single infection.
How does it do this? The measles virus latches onto these memory cells, holding them hostage. To defeat the infection, your body destroys not just the virus but the memory cells it hijacked.
Unfortunately, destroying a memory cell also means destroying that cell’s ‘photo’ of a dangerous germ. And without a photo record, the immune system forgets its old enemies. So when an old germ returns, it looks like a stranger. This is why the body loses up to three-quarters of its immune memory after a measles infection.
Your body can make new memory cells. But they won’t carry the photos from before.
The Big Picture
So far, we’ve been talking about cells. But what does this all mean for real people?
It means that their immune system is basically reset to that of a young child’s. If they’ve gotten chicken pox before, they might get it again. If they had been vaccinated for different types of infections, those vaccinations might not work anymore (so they’ll need to be vaccinated again). And for the next 2–3 years, they’ll catch a lot of colds and stomach bugs, just like a child going to school for the first time.
Why Measles Vaccination Matters
Vaccination is safe and effective. Two doses of the MMR (measles, mumps, and rubella) vaccine is 97% effective at preventing measles. These shots give your body a ‘photo’ of the virus without causing immune amnesia.
And not only does vaccination protect you against measles, it also protects you from all the infections you’re likely to catch after measles. It’s a package deal!
Sources:
Centers for Disease Control and Prevention. Measles cases and outbreaks. Accessed September 3, 2025. https://www.cdc.gov/measles/data-research/index.html
de Vries RD, McQuaid S, van Amerongen G, et al. Measles immune suppression: Lessons from the macaque model. PLoS Pathog. 2012;8(8):e1002885. https://www.doi.org/10.1371/journal.ppat.1002885
Hagen, A. Measles and immune amnesia. American Society for Microbiology. February 27, 2024. https://asm.org/articles/2019/may/measles-and-immune-amnesia
Mina MJ, Metcalf CJ, de Swart RL, Osterhaus AD, Grenfell BT. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science. 2015;348(6235):694-699. https://www.doi.org/10.1126/science.aaa3662
Mina MJ, Kula T, Leng Y, et al. Measles virus infection diminishes preexisting antibodies that offer protection from other pathogens. Science. 2019;366(6465):599-606. https://www.doi.org/10.1126/science.aay6485
Leave a Reply