Immune Amnesia: How the Texas Measles Outbreak Could Promote the Spread of Other Infectious Diseases

In the years before the introduction of the measles vaccine, the disease infected more than half a million people and killed hundreds of children each year in the United States alone.¹ After the approval of the vaccine in the 1960s, these numbers dropped precipitously and in 2000, the World Health Organization declared that measles had officially been eliminated from the country.

But in late January 2025, a measles outbreak erupted in Gaines County, Texas. Within weeks, it had spread across state lines to New Mexico and Oklahoma, sickening nearly 300 people. Two deaths have been reported so far—the first measles deaths in the US in a decade.

Many of the nastier measles complications were discovered decades ago: Children can die from pneumonia and encephalitis, pregnant people may give birth prematurely, and in extremely rare cases, individuals develop subacute sclerosing panencephalitis seven to 10 years after their initial infection.² This progressive neurological disorder is almost invariably fatal.

Only in the last decade have researchers discovered and characterized another consequence of measles infection that is both common and insidious: immune amnesia. Essentially, the measles virus causes the immune system to “forget” previously acquired immunity, both from vaccinations and infections, leaving children vulnerable to a host of other pathogens for the following two to three years.³

“What we see is almost like a shadow of mortality following a measles outbreak,” said Michael Mina, an epidemiologist and coauthor of the 2015 study, which demonstrated that measles cases in the US, UK, and Denmark were strongly correlated with rates of childhood mortality attributed to non-measles infectious diseases in the 18 to 30 months that followed an infection. Formerly at the Harvard T.H. Chan School of Public Health, Mina now serves as Executive Chairman for C2Sense, a company developing diagnostic technologies.

Immune Amnesia: From Epidemiology to Mechanisms

Mina has long been interested in the unexpected sequelae of infectious diseases. During his medical and graduate training at Emory University in the early 2010s, Mina studied the effects of influenza—and vaccination against it—on an individual’s risk for developing other types of viral or bacterial infections. Mina said, “It brought me into this whole mode of thinking about, ‘how else do viruses impact our bodies in weird ways? And what are the consequences of that?’”

In the course of this research, Mina read a 2012 study by Rik de Swart, a virologist at Erasmus University, that piqued his curiosity.⁴ De Swart’s group used glowing green proteins to track the measles virus as it spread throughout animals’ bodies. They watched as the virus entered and multiplied inside memory T cells and follicular B cells, which are important for antibody responses; these infected cells were then cleared away by other immune cells. “When I came across Rik’s paper on measles, I thought, ‘Wow, this is really interesting—measles kills immune cells!’” said Mina. “But at the time, there wasn't really much discussion about the long-term ramifications.”

In 2013, Mina moved on to a postdoctoral position at Princeton University, where he worked with infectious disease dynamics researchers Jessica Metcalf and Bryan Grenfell. The Princeton team joined up with de Swart and began to comb through the epidemiological data, looking for clues that might indicate population-level immunological dysfunction following measles outbreaks.

In 2015, they published their findings on the link between measles and infectious disease fatalities and in 2018, a subsequent study of thousands of children in the UK demonstrated widespread effects on nonfatal infections as well.^3,5 Researchers found that after contracting measles, children were 43 percent more likely to see a doctor for another type of infection in the first month post-measles, 22 percent more likely between one month and one year, and 10 percent more likely from one year to 2.5 years, in comparison to their demographically-matched peers who did not contract measles.

Meanwhile, in vitro studies by de Swart’s research team had demonstrated that a subset of immune cells called plasma B cells were especially susceptible to measles infection.⁶ “Plasma cells are very special cells,” explained Mina. “When your body creates B cells in response to an infection, a very small fraction of those B cells migrates into the bone marrow, and they set up shop and become your long-lived antibody-producing factories against that infection.” If measles also attacked the plasma cells in vivo, the immunological consequences could be severe indeed. “Plasma cells are terminally differentiated, which means they don’t divide again,” explained Mina. “So, if you kill a plasma cell, you've killed like a whole antibody-producing factory… and we don't have a lot of plasma cells.”

Since long-lived plasma cells are tucked away in the bone marrow, it can be tricky to study them in humans, especially in children, whose parents may be understandably reluctant to subject them to a painful bone marrow biopsy. The antibodies produced by these plasma cells, however, can be measured using a single drop of blood. “Literally 0.2 microliters of blood has a representation of your whole immunological memory in it,” said Mina. These antibodies provide a detailed record of an individual’s history of infections and vaccinations.

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Along with Harvard University geneticist Stephen Elledge, Mina, de Swart, and a dozen others analyzed the pathogen-targeting antibodies present in blood samples from children before and after a measles infection. In the approximately ten weeks between the pre- and post-measles blood samples, children with mild cases lost about 33 percent of the antibody types their blood contained in the pre-measles assessment; those with severe cases lost an average of 40 percent.⁷ While some variation is normal, “Ninety percent of your antibody repertoire is super stable,” said Mina. Indeed, two separate control cohorts, sampled three months and one year apart, maintained about 90 percent of their antibodies and did not show any significant change in overall antibody diversity.

In the children who contracted measles, the lost antibodies recognized epitopes from various types of clinically important viruses, including enteroviruses, herpesviruses, respiratory syncytial virus, and influenza virus. In agreement with previous studies, total antibody levels as measured by immunoglobulin proteins were largely unchanged—as many types of antibodies were lost, “You're refilling the pool with antibodies against measles,” said Mina.

This antibody diversity doesn’t recover on its own, he said, “You have to repopulate it with new memories, by getting new vaccines or new infections.”

This immune amnesia could have profound implications for global health and could be an important element in the design of vaccination campaigns and in epidemic disease modeling. For example, a study in the Democratic Republic of the Congo revealed that among children who were fully vaccinated against tetanus, those who had contracted measles were more likely to have subprotective levels of tetanus antibodies.⁸ Another research group concluded that measles-induced immune amnesia could have important effects on outbreaks of other diseases, enabling epidemics to spread even in areas with high vaccination coverage for that particular pathogen.⁹

The Side Effects of Misinformation

What can be done to prevent this dangerous and long-lasting immune impairment? In a small 2024 study in ferrets, an experimental antiviral helped mitigate a similar type of immune amnesia, but this drug has not been tested for safety or efficacy in humans.¹⁰ There is, of course, another option, which has been in use since the 1960s, and has a track record of safety and efficacy for preventing measles infection as well as long-term sequelae like immune amnesia: vaccination.

Unfortunately, vaccination rates have been falling in recent years. In 2019, the World Health Organization listed vaccine hesitancy as one of the top ten threats to global health.¹¹ In 2023, a CDC report found that in the US, the proportion of fully vaccinated kindergarteners fell below 93 percent, with vaccination rates as low as 80 percent in some states. Because measles is incredibly infectious, public health experts estimate that about 95 percent of people need to be vaccinated to maintain herd immunity.

As Mina pointed out, fears and misinformation related to vaccines are nothing new. “Ever since vaccines [were discovered], people have criticized them and ridiculed them,” he said. “If you don't intimately understand how the immune system works…then you’d think that putting a pathogen into somebody is just wrong and bad.”

Indeed, just one year after Edward Jenner published History of the Inoculation of the Cow-Pox—his findings on vaccination with cowpox as protection against the far more deadly smallpox—there was already substantial backlash.¹² In a treatise published in 1800, physician Benjamin Moseley expressed these somewhat hysterical concerns: “Can any person say what may be the consequences of introducing the Lues Bovilla, a bestial humour—into the human frame, after a long lapse of years?...Who knows, also, but that the human character may undergo strange mutations from quadrupedan sympathy; and that some modern Pasiphaë may rival the fables of old?”¹³ (Pasiphaë, a figure from Greek mythology, was cursed to fall in love with a bull, and subsequently conceived the Minotaur.)

While the specific concerns have varied, fears and misinformation about vaccines continue to periodically resurface throughout the centuries. “The current outcry, the current wave of anti-vaccination, really started with Wakefield and [measles, mumps, and rubella] vaccines, saying they create autism,” said Mina. Although Wakefield’s studies were determined to have crucial scientific flaws, and subsequent studies of hundreds of thousands of children revealed no differences in autism prevalence between vaccinated and unvaccinated children, safety concerns have lingered in the minds of many parents.¹⁴ Anti-vaccination influencers and public figures, perhaps most notably Robert F. Kennedy Jr., who is now the US Secretary of Health and Human Services, have stoked these concerns via popular podcasts and social media, spreading false claims about the dangers of vaccines.¹⁵

It is precisely because widespread use of this highly effective vaccine had all but eliminated measles in many countries, that parents believe that their child’s risk of encountering this virus is extremely low. This affects how they weigh the risks and benefits of vaccination, especially when misinformation about the risks is rampant. “You might have a 35-year-old mother who's saying, ‘I've never seen measles, so why would I inject my kid with this thing?’” said Mina. “Anything you do to a healthy baby is going to lead to concern and fear, which is why we have to be so much more careful and empathetic than—generally speaking—doctors are today. I feel like it's become like a nightmare scenario of people deriding their patients for not vaccinating [their kids], when actually the patients are just scared.”

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Mina called for compassion and increased communication by public health and medical professionals. “If vaccines are going to be so good that they eliminate the very threat we're concerned about, then the onus is on us to continuously educate and not assume that we can rest on our laurels and just say, ‘Well, of course vaccines are good.’”

An individual unvaccinated child—or even a small group of them—can be protected by the herd immunity of those around them. But in many places, herd immunity is no longer guaranteed. Globally, most countries currently fall below the 95 percent vaccination threshold, and of the 82 countries with verified measles elimination, just 34 percent met these vaccination targets, making their elimination status somewhat precarious.¹⁶

“What we're seeing in Texas—and what we're going to see—is what happens when we allow those vaccine-hesitant bubbles to grow too big,” said Mina. “Those kids are no longer protected by herd immunity, and the reason is because the bubbles start fusing into each other…all of a sudden, one outbreak [can ignite] the whole thing.”