Measles infection causes ‘immune amnesia,’ leaving kids vulnerable to other illnesses

When it comes to measles, the opposite is true, according to two studies published Thursday.

By MELISSA HEALY
A vial of the measles, mumps, and rubella virus (MMR) vaccine is pictured at the International Community Health Services clinic in Seattle, Washington, U.S., March 20, 2019. Picture taken March 20, 2019 (photo credit: REUTERS/LINDSEY WASSON)
A vial of the measles, mumps, and rubella virus (MMR) vaccine is pictured at the International Community Health Services clinic in Seattle, Washington, U.S., March 20, 2019. Picture taken March 20, 2019
(photo credit: REUTERS/LINDSEY WASSON)
It’s an article of faith for many who refuse to have their children vaccinated against childhood diseases: when healthy children get and recover from an infection naturally, their immune systems come out stronger.
When it comes to measles, the opposite is true, according to two studies published Thursday.
In a group of 77 Dutch schoolchildren whose parents declined to vaccinate them on religious grounds, the new research documents several ways in which infection with measles can hobble a child’s immune function for months or even years after that child has recovered from her bout with the virus.
The effect was mild in some of the children. But in roughly 16% of those who suffered an active measles infection, the result was a severe case of “immune amnesia.” In those children, a genetic census of antibodies – immune proteins that recognize and destroy invading microbes – showed that they had lost at least some immunity to more than 40% of common childhood diseases. Measles appeared to have stripped away immune protections these children had built over years of exposure to diseases and germs.
Measuring the same children’s immune memory 40 days after measles infection, a second team found significant shrinkage in their stores of B-cells, which fight disease by killing infected cells and spawning legions of antibodies to confront viral invaders in the blood. For weeks after the unvaccinated children had recovered from measles, their depleted stocks of B-cells signaled a loss of memory for past infections and of strength to mount a defense against new infections.
For some, the damage appeared to be even more extensive. In two of 19 measles-infected children tested, the machinery that supplies the immune system with new disease-targeting cells was profoundly disrupted, raising questions about whether they would fully recover their previous strength.
“The measles virus is like a car accident for your immune system,” said Harvard University geneticist Stephen Elledge, one of the paper’s co-authors. An unvaccinated child who weathers the measles may emerge only slightly the worse from such a crash. Or he might sustain an injury from which it that takes months or years to recover.
For parents, the studies’ implications are clear, Elledge added. “We know how to prevent injuries in car accidents – by wearing seatbelts. The measles, mumps and rubella vaccine is like a seat belt for your immune system, and parents should buckle their kids up.”
The studies were published Thursday in the journals Science and Science Immunology.
The research sheds new light on the biological basis for a mysterious phenomenon long recognized by doctors. After children recover from the measles’ hallmark rash and fevers, they are highly unlikely to fall ill with it again. But for two to three years following infection, patients remain unusually vulnerable to catching or developing other infections, from viruses like the common cold and influenza, to potentially deadly bacterial infections that can cause pneumonia or swelling in the brain.
Researchers reckon that before the introduction of a measles vaccine in 1963, as many as half of childhood deaths from infectious diseases were linked to measles or the immuno-suppression that follows. In that period, this most contagious of viruses infected over 95% of all children and directly caused more than 4 million deaths a year.
But in places where vaccine campaigns have virtually eliminated outbreaks, public health officials have documented unexpectedly large reductions in childhood deaths from other diseases. Preventing infection with measles was clearly saving kids from succumbing to other bugs as well, experts say.
The mystery of how measles sets kids up for poorer health might have lost its urgency if global vaccine campaigns were expanding without pushback. But they are not. Every year, more than 7 million people, mostly in poor countries, are still infected, and roughly 100,000 die of measles.
And in recent years, an uptick of vaccine refusal in the United States and Europe has reversed decades of rising vaccination rates in the world’s most affluent countries. In the first three months of 2019, parents’ reluctance to have their children vaccinated helped drive worldwide cases of measles up 300% over cases reported in the first quarter of 2018, according to the World Health Organization.
The United States declared measles eliminated in 2000. But pockets of “anti-vaxxers” have allowed it to gain a foothold in communities across the nation. Between January 1 and October 1 of this year, there have been 22 US outbreaks of measles. Of 1,250 cases documented in 31 states during that period, 89% of patients were unvaccinated or did not know their vaccination status.
Not since 1992 has the tally of measles cases in the United States reached so high. While none have died, 119 required hospitalization and 60 developed pneumonia. One patient suffered encephalitis, a life-threatening swelling of the brain.
“Measles is not a trivial disease, and these findings add evidence that it’s important to vaccinate your kids against it,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. “There’s scientific proof here that not only is measles itself a serious disease; it can have consequences of suppressing the body’s defense mechanisms for a year or more.”
THE TWO new studies’ human subjects belong to a part of the vaccine-refusal movement with deep roots. Members of a Dutch sect of orthodox Protestants, they form a closed community within Dutch society, with their own churches, schools, newspapers and political party. Since the 19th century, when vaccination campaigns gained steam and drew protests throughout the United States and Europe, these Dutch Protestants have declined vaccination. Their opposition rests on passages in the Bible that call on believers to trust in divine providence for protection.
In the United States, those opposed to vaccination on religious grounds have remained a steady presence. But discredited claims that the measles, mumps and rubella vaccine is a cause of autism have driven down vaccination rates in pockets across California, New York and elsewhere and prompted “vaccine reluctance” among many parents. Most recently, false claims circulating among members of New York City’s Orthodox Jewish community – that MMR vaccine contains monkey, rat and pig DNA and contravenes kosher dietary requirements – have figured prominently in recent outbreaks. More than three-quarters of measles cases in the United States this year have been in New York.
The Dutch school children in the new studies, who ranged in age from four to 17, were followed for only up to eight weeks after their infections. But each team also conducted animal studies that found measles affects immunity in real and enduring ways.
One of the teams, based in the Netherlands and United Kingdom, used ferrets to demonstrate post-measles vulnerability to flu. Even after they had been immunized against influenza, ferrets who were infected with measles and then exposed to flu virus got much sicker than ferrets who had not had measles.
A second team, led by Harvard epidemiologist Michael Mina and geneticist Stephen J. Elledge, assessed the array of antibodies in four rhesus macaque monkeys before and after measles infection and found that for five months after their infections cleared, the monkeys sustained a loss of immunity to an average of 40% to 60% of diseases.
Mina and Elledge said their work offers new insights into the longstanding mystery of how measles seems to put children at increased risk of infections. And, they added, it underscores the outsize value of a simple protective step: having a child vaccinated with the MMR vaccine just after her first birthday and again between the ages of 4 and 6.
Such evidence may not sway the most committed vaccine opponents, Mina said, but “most people are really trying to do what’s right for their kids.” Even when those parents are inclined to believe their child could weather a bout of rash and fevers, he added, “telling them that for the next few years, they’re going to have to look over their kid’s shoulder at diseases he might get sick from, that makes this amnesia effect quite a bit more scary.”


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