Measles is known to make children vulnerable to other infections. Now two major studies of Dutch Orthodox Protestants, who reject vaccination, have discovered why: it massively damages the immune system, making measles even more lethal than we realised.
That is bad news, as measles cases worldwide rise to levels not seen since 2006, increasing tenfold in Africa and doubling in Europe. They have reached the highest numbers in years in the US and England. There were 7 million cases worldwide in 2017, but figures expected to be published this December show that numbers rose “substantially” in 2018, says Katrina Kretsinger of the World Health Organization.
“All cases are because people who should have been vaccinated were not,” she says, because of weak health systems, poor public information and anti-vaccine sentiment.
After measles vaccination was introduced in the 1960s, cases fell dramatically. Mysteriously, wherever that happened, deaths from completely unrelated infections also dropped.
Vulnerable to other infections
In 2015, Michael Mina, now at Harvard University, found that children who have had measles are so much more likely to catch other diseases that such post-measles infections may account for half of all infectious disease deaths in children living in areas where measles circulates.
Around 100,000 children died of measles in 2017. Mina suspects that two or three times that number who had measles will later die of other infections they would not have caught if they hadn’t had measles.
Now we know why. As we are exposed to pathogens as children, we accumulate specialised immune cells, each of which has learned to make antibodies to attack one particular bit of a pathogen. The measles virus kills these cells, but the impact of this wasn’t known.
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Mina and his team determined what antibodies were made by 77 unvaccinated Dutch children who later caught measles. Before any of them had measles, these children could make antibodies to many viruses and bacteria. But afterwards, they lost between 11 and 73 per cent of their library of antibodies, for all kinds of pathogens.
Wiped-out immune system
“The worst-affected 20 per cent lost more than half the antibodies they could make against more than half the pathogens we tested,” says Mina. The live, weakened measles virus in the MMR vaccine had no such effect in the 32 other children they studied.
To get their lost antibodies back, Mina suspects those who had measles must be re-exposed to all the pathogens they had already encountered, with the attendant risks of disease. They may even need to receive any previous vaccinations again, as vaccines work by teaching the immune system to make specific antibodies.
It might even be worse than that. In another study out this week, Colin Russell at the University of Amsterdam in the Netherlands and his colleagues sequenced the DNA of immune cells from 20 of the same group of children. “We could look not just at cells producing antibodies, but at their naive, precursor cells,” says Russell.
Resetting the system
In our first few years of life, these naive cells mature, diversifying so they will rapidly recognise particular types of molecules on different pathogens. Russell’s team found that measles kills the mature cells. “It’s as if our immune system is reset back to infancy.”
That means, he says, that those who have had measles may need to be re-exposed to diseases multiple times to rebuild their antibody repertoire.
It could take five years for their immune systems to recover, as this is how long it takes in people given the powerful immunosuppressive drug rituximab, which depletes the same cells and is used to treat some kinds of cancer. This agrees with studies showing that people who have had measles have lowered immunity for up to five years.
The effect has real clinical impact. Russell’s team gave a virus similar to measles to ferrets vaccinated against flu. These animals went on to have bad bouts of flu. Vaccinated ferrets who didn’t get the measles-like virus were still protected against flu.
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