Measles can cause long-term damage to the immune system – resetting it to a baby-like state and leaving people vulnerable to other infections, scientists have said.
According to new research, the measles virus deletes part of the immune system’s memory, removing previous immunity to other infections in both humans and ferrets.
Research from the Wellcome Sanger Institute, University of Amsterdam and their collaborators showed that the disease resets the human immune system to an immature state with only limited ability to respond to new infections.
Published in the journal Science Immunology, the study explains why children often catch other infectious diseases after measles.
Scientists said the research has great implications for public health, as falling vaccination rates are resulting in rising cases of measles.
They said this in turn could cause an increase in cases of other dangerous infections such as flu, diphtheria or tuberculosis, even in people who were previously immune.
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Lead author Dr Velislava Petrova, from the Wellcome Sanger Institute and Cambridge University, said: “This study is a direct demonstration in humans of ‘immunological amnesia’, where the immune system forgets how to respond to infections encountered before.
“We show that measles directly causes the loss of protection to other infectious diseases.”
To see what measles does to the immune system, researchers recruited a group of 26 unvaccinated, otherwise healthy children in the Netherlands. They took blood samples, which were followed up with a repeat sampling after a measles outbreak in 2013. The researchers sequenced antibody genes from the children both before and 40-50 days after their measles infection.
The scientists found that specific immune memory cells that had been built up against other diseases, and were present before the measles virus infection, had disappeared from the children’s blood.
This “immunological amnesia” was then tested in ferrets, showing that infection with a measles-like virus reduced the level of flu antibodies in the animals that had been previously vaccinated against flu.
Researchers also found that the measles virus resets the immune system to an immature state which can only make a limited repertoire of antibodies against disease.
What’s in the MMR vaccine?
The active ingredient of vaccines can vary dramatically – they might take the form of live (but weakened) viruses, completely inactivated viruses or just fragments of a virus or bacteria. There are numerous ways the vaccine might be administered, for example, orally, nasally or by a jab. These factors require different components to make the vaccine easy to produce, effective and stable.
Take a look at the make up of a single dose of a measles, mumps and rubella jab
Professor Colin Russell, senior author from the University of Amsterdam, said: “For the first time we see that measles resets the immune system and it becomes more baby-like, limiting how well it can respond to new infections. In some children the effect is so strong it is similar to being given powerful immunosuppressive drugs.
“Our study has huge implications for vaccination and public health as we show that not only does measles vaccination protect people from measles, but also protects from other infectious diseases.”
In the late 1960s a highly effective measles vaccine was introduced in the UK, and in 2017 the disease had been completely eliminated from the country.
However, measles is highly contagious and cases are rising again, with the UK’s vaccination uptake dropping below the required level of 95 per cent of the population.
This led to the UK losing its World Health Organisation (WHO) measles elimination status in August.
In a separate study published in the Science journal, researchers used a tool called VirScan to analyse the responses of antibodies in 77 unvaccinated children aged 4 to 17 before and after measles infection.
The technology tracks antibodies to thousands of viral and microbial antigens in the blood.
Led by investigators at Harvard Medical School, Brigham and Women’s Hospital and the Harvard TH Chan School of Public Health, scientists found the disease wiped out 11 to 73 per cent of the antibody repertoire across individuals 2 months after measles infection.
Professor Michael Mina said: “Imagine that your immunity against pathogens is like carrying around a book of photographs of criminals, and someone punched a bunch of holes in it.
“It would then be much harder to recognise that criminal if you saw them, especially if the holes are punched over important features for recognition, like the eyes or mouth.”
Prof Mina and colleagues found those who survive measles gradually regain their previous immunity to other viruses and bacteria as they get re-exposed to them.
However, because this process may take months to years, people remain vulnerable in the meantime to serious complications of those infections.