T cells are seen here attacking a cancer cell. The measles virus not only uses T – and B – cells as a ride around the body, but also feeds on them, thus destroying the immune system’s memory of how to fight off previous infections. — 123rf
Dr Adam Ratner has heard a lot of myths and misunderstandings about measles in his decades as a New York City paediatric infectious disease specialist in the United States.
A troubling untruth he’s seen circulating on social media during the current measles outbreak in the US is that being infected with the virus instead of getting vaccinated confers benefits on the immune system – a strength-training programme of sorts for the cells.
The truth, he said, “is exactly the opposite.”
Immunity at an expense
Measles is a highly contagious virus that presents as a rash and with cold-like symptoms for many patients, and can lead to serious or fatal complications for others.
An outbreak that began in west Texas in January has since infected nearly 500 people across 19 US states.
An insidious but lesser-known consequence of even a mild measles infection is that it kills the very cells that remember which pathogens the patient has previously fought and how those battles were won.
As a result, recurring bugs that might have caused only minor symptoms make patients as sick as if they’d never encountered them before.
Measles destroys lymphocytes that defend against other bugs to make way for ones that defend against measles, an immunity won at the cost of other protections.
This “immune amnesia”, physicians say, leaves patients vulnerable to recurrences of diseases their immune cells were previously able to resist.
If a child gets sick with measles, “for the next two or three years, you kind of have to be looking over your kid’s shoulder, wondering if some otherwise routine virus or bacteria that they should be very well protected against is potentially going to land them in the hospital,” said epidemiologist Dr Michael Mina, who was previously an assistant professor of immunology and infectious diseases at Harvard Medical School.
“Even if your measles virus infection seemed mild and you kind of blew through it, it doesn’t mean that it was mild on your immune system,” he said.
Take rotavirus, for example, Dr Ratner said.
This infection causes severe diarrhoea that can be life-threatening for children if untreated.
A child who has rotavirus once will have antibodies that offer protection against future infections.
But a measles infection, said Dr Ratner, author of the recent book Booster Shots: The Urgent Lessons of Measles and the Uncertain Future of Children’s Health, “could wipe out that immunity and they could be just as vulnerable to rotavirus as if they had never seen it before.”
Killing off immune cells
Immune amnesia results from the measles virus’ plan of attack.
Viral particles travel via airborne droplets of saliva, mucus and cells that make their way into a new body when their unsuspecting host breathes them in.
From there, they sneak past the protective barrier lining the respiratory system and head to the lymph nodes in search of cells that express a particular protein called signalling lymphocytic activation molecule (SLAM).
The virus then rides around the bloodstream on these hijacked SLAM-expressing cells, further infecting and destroying other SLAM expressers it meets on the way.
Among the SLAM-expressing cells that measles wrecks are memory B and T cells, two crucial players in a functioning immune system.
Memory B cells manufacture the right antibodies quickly when a familiar microbe appears.
Memory T cells recognise and kill viruses that your cells have encountered in the past.
A measles infection feeds on these memory cells.
Vaccines, in contrast, stimulate the production of memory B and T cells without consuming others in the process.
Before and after
This was not yet understood in the decades before the measles, mumps and rubella (MMR) vaccine’s approval in 1963, when measles was a common childhood disease that killed some 400 children in the US each year.
“For 100 years or more, we’ve known that measles does cause an acute susceptibility to other infections,” Dr Mina said.
A measles infection temporarily suppresses the immune system, he said, and it was long assumed that opportunistic infections around the time of the illness were the result of that short-term suppression.
In 2015, Dr Mina and his colleagues published a paper that looked at mortality (death) data in the US, Britain and Denmark before and after measles vaccines were introduced.
They found that whenever there were measles outbreaks, childhood deaths from all other infectious diseases remained significantly higher for two to three years in outbreak locations – an increase that accounted for up to half of all childhood deaths from infectious disease.
Once those countries rolled out the MMR vaccine, measles cases fell, as expected.
But so did childhood deaths from other infectious diseases, by about half.
Three years later, Dr Mina and his collaborators took blood samples from 77 unvaccinated children in a community in the Netherlands before, and then two to six months after, the children contracted measles.
They found that the virus wiped out 11% to 73% of the children’s pre-existing antibodies to a host of pathogens.
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Just as children in preschool fall ill constantly with common diseases they’re encountering for the first time, unvaccinated children who contract measles are at higher risk in the ensuing years for common early childhood sicknesses such as respiratory infections, ear aches and viruses that cause diarrhoea, said Associate Professor Dr Shelly Bolotin, a scientist at Public Health Ontario in Canada and director of the Center for Vaccine Preventable Diseases at the University of Toronto.
“In order to correct that depletion [of B and T cells], you need to be re-exposed to everything you were immune to before, and this can take years,” she said.
Protection without consequences
As of late March (2025), 97% of the people sickened in the current US measles outbreak were unvaccinated or didn’t disclose their vaccine status.
The measles virus is attenuated in the MMR vaccine, meaning that it has been altered to produce the appropriate immune response without triggering the disease itself.
In the case of measles, that means no mass destruction of the cells that hold the immune system’s memory.
“It doesn’t have this very, very damaging effect, which is why we recommend vaccination, because we get all of the immunity with none of the adverse consequences,” Assoc Prof Bolotin said. – By Corinne Purtill/Los Angeles Times/Tribune News Service
