Don’t You Forget About Me(asles): The Virus That Erases Immune Memory

Measles vaccination protects your entire immune history.

TL;DR:

• Measles causes “immune amnesia,” wiping out a significant proportion of your immune system’s memory of past infections.

• This immune amnesia can increase your susceptibility to other infections for years.

• Vaccination prevents measles-induced immune amnesia.

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With measles cases on the rise, there is yet another important reason to avoid this virus. Besides making you seriously sick, measles can erase your immune memory to other infections.

This fascinating and terrifying phenomenon is known as “immune amnesia”-basically a reset of the immune system to its immature state. Something different about measles and the immune system was first suspected when the global roll-out of measles vaccination led to dramatic drops in child mortality that were larger than could be explained by reduced measles deaths alone. Could measles vaccinations really protect kids from dying from all other infections?

Exploring this idea further, a 2015 study of data from the U.S., U.K., and Denmark found that mortality from non-measles infections moved up and down closely with the incidence of measles at the population level with a lag of up to 2-3 years. The authors dubbed this the “measles shadow.”

Source: Mina et al. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science 348,694-699(2015)

The first study to confirm measles amnesia at the individual level was published in 2019 and followed unvaccinated Dutch children during an outbreak, collecting blood samples before and after a confirmed measles infection. The researchers used a nifty test called VirScan that detects antibodies to a long list of different pathogens. They found that kids lost up to 73% of their immune memory repertoire to other pathogens after a measles infection. The only way to rebuild this immune memory was to be exposed to these infections all over again, so their immune system could re-learn how to fight all the pathogens they'd already encountered​.

In contrast, kids who got the MMR vaccine didn’t lose any immune memory, and their immune repertoire stayed stable or even grew.

Source: Mina et al. Measles virus infection diminishes preexisting antibodies that offer protection from other pathogens. Science 366, 599-606 (2019). Red dots represent kids infected with measles, green uninfected from the same community, “controls” A and B are people with no known exposure.

How does measles erase immune memory, while also inducing such strong lifelong immune memory to measles itself? Like many things in the immune system, it’s complicated. To oversimplify, measles directly infects lymphocytes including B and T memory cells aimed at other pathogens and destroys them. You can read more in this piece in Science Immunology whose title I seriously covet: “Game of Clones: How measles remodels the B cell Landscape.”

Your immune cells know nothing, Jon Snow.

Bottom Line

Measles is nasty enough, but “immune amnesia” puts it in a special class. Sadly, measles is making a comeback. This means the "measles shadow” could also make a comeback, with increased risk from all other infections lingering for years in survivors. So remember that the highly effective measles vaccine doesn’t just protect against measles disease, hospitalization, and death- it protects your entire immune history.

For more info on the recent measles outbreaks and who may need updated vaccination, check out these updates from

Those Nerdy Girls

here and

Elisabeth Marnik, PhD

here.

Stay well,

Jenn

Your immune system--not forgetting anything.