Measles: A Hidden Threat to Children's Health
The recent surge in measles cases in the US has sparked concern among healthcare professionals and parents alike. While the immediate dangers of the virus are well-known, a lesser-known consequence poses a significant threat to children's health: immune amnesia.
Immune amnesia is a condition where the virus destroys immune memory, wiping out memory B cells and T cells, and forcing the immune system to rebuild its defenses from scratch. This leaves patients vulnerable to new exposures and infections, with potential long-term consequences.
"Nearly every unvaccinated child who gets measles can be impacted," says Patricia Stinchfield, CPNP, past president of the National Foundation for Infectious Diseases. "Rebuilding immune memory leaves patients vulnerable to new exposures, and infections, hospitalizations, and missed work and school can linger for up to 5 years."
Immune amnesia was officially recognized in 2015, but clues emerged much earlier. Scottish scientists in the 1700s described waves of infections and deaths in the wake of measles. When measles vaccines arrived in the 1960s, '70s, and '80s, researchers noticed unexpected drops in seemingly unrelated health problems.
Michael J. Mina, MD, PhD, an infectious disease expert and former assistant professor of epidemiology and immunology at Harvard Medical School, says: "Half of all childhood infectious-disease deaths were related to immune amnesia caused by measles. Before vaccines, it was difficult to see the connection because virtually everyone got measles. There was no one to compare them to."
Experts once believed that measles suppressed immunity for only a few weeks, but evidence began mounting after the turn of the century that its effects lasted much longer.
Japanese researchers made a breakthrough in 2000 when they identified a unique interaction with immune cells. The measles virus binds to a receptor called CD150, an immune memory cell marker, and then travels from the lungs to lymph tissue, using those cells to replicate.
Mina's 2015 study, published in Science, demonstrated the long-term impact. Graphs in the study showed dramatic drops in non-measles deaths in the decades after the vaccine was introduced in the US, Denmark, England, and Wales. "The results were so striking," Mina said. "This wasn't just statistical magic."
Another breakthrough came when Harvard researchers unveiled VirScan, a biological scanner that detects a wide range of antibodies from a small blood sample. Researchers now had a tool to track changes in infection-fighting antibodies, but they needed before-and-after samples from children who'd had measles.
Virologist Rik de Swart, PhD, an associate professor at Erasmus Medical Center in Rotterdam, Netherlands, had collected blood samples from infected and uninfected children during a 2013 measles outbreak in Amsterdam. Their 2019 Science study was the first to measure the immune memory loss following infection, finding dramatic losses in some children.
"The kids who had measles lost 11%-73% of their whole immunological memory pool," Mina said. "Overall, half of their total memory cells were gone."
This provided the biological explanation for immune amnesia.
The risk of infection remains high for children who contract measles. While modern medicine likely reduces the risk of death from immune amnesia, children who get measles can expect more illnesses for the next couple of years.
An analysis of health records from 1990 to 2014 found that the month following measles infection is the riskiest. Unvaccinated children were 43% more likely to catch another infectious illness, 2.7 times more likely to be hospitalized, and three times more likely to receive a prescription anti-infective. The risk remained 22% higher for the rest of the year and 10%-15% higher for 2-5 years.
De Swart says the health risks of immune amnesia are likely greater in low-income countries with poor hygiene and weak healthcare systems, leading to higher morbidity and mortality.
Studies in the Democratic Republic of the Congo found that children who received tetanus vaccines and later had measles created fewer tetanus antibodies than those who didn't get measles. Measles was also linked to more post-infection fevers in young children.
James D. Cherry, MD, Distinguished Professor in Pediatric Infectious Diseases at the David Geffen School of Medicine at UCLA, says: "There's this perception that measles is no big deal. But measles is bad for a lot of reasons no matter where you live."
New research is exploring ways to measure immune amnesia and test antiviral treatments that might interrupt the process. Johns Hopkins researchers found that the antiviral drug remdesivir reduced antibody loss, suggesting early therapeutic intervention could decrease morbidity and mortality from measles-induced susceptibility to other infections.
In the Netherlands, researchers at Erasmus Medical Center are launching a study of 100 children and teens, half vaccinated, half unvaccinated, to track their health and changes in antibodies and immune memory cells over 3 years.
"We plan to look at the loss of immunity to other pathogens after measles," said lead researcher Corine Geurts van Kessel, MD, PhD. "Of course, we would also like to examine what kinds of infections these children experience, but the study is likely too small. Immune amnesia is definitely a health risk."
Measles already carries well-known risks and complications, including ear infections, diarrhea, a 20% risk for hospitalization, a 5% risk for pneumonia, a 1 in 1000 chance of brain swelling, up to 3 in 1000 odds of death, and about a 1 in 10,000 risk for subacute sclerosing panencephalitis (an often-fatal neurologic disorder).
"Parents should find comfort in the knowledge that vaccine safety science is robust and the best way to keep your child healthy and safe is to vaccinate," Stinchfield said.
Cherry agreed. "Most patients thankfully still trust their pediatrician and primary care doctor," he said. "Educate your patients about immune amnesia: Physicians need to talk about the risks of not being vaccinated."
The effects of immune amnesia after recent US outbreaks have not been formally documented, but an unpublished survey of a 2018-2019 New York state outbreak found twice as many infections in unvaccinated, measles-infected children in the year after they were diagnosed compared with uninfected kids, most of whom were vaccinated.
In the US and other developed countries, unvaccinated children and teens who get measles are most likely to experience a few more infections for the next 2-5 years compared with vaccinated peers, and those illnesses may be more severe. "It's the stuff kids are already susceptible to such as colds, flu, respiratory syncytial virus, COVID, and adenoviruses that can cause respiratory and digestive-system symptoms," Mina said. The added risk lasts until the immune system rebuilds.
"Discussing the ramifications of a measles infection with parents is really important," he said. "This isn't just the measles. There's more to it. Our healthcare system gets kids through acute infections really well. But when your child is getting 3 or 4 or 5 extra infections a year, it adds up."
