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Getting infected with measles is much more dangerous than scientists once suspected. In addition to the illness caused by the virus, a measles infection also takes a wrecking ball to the immune system. It destroys as much as half of the existing antibodies that protect against other viruses and bacteria, new research said.

That means people, especially children, who get measles become much more vulnerable to other germs that cause diseases such as pneumonia and influenza that they had previously been protected against.

The discoveries have enormous public health implications, researchers and clinicians said. In recent years, anti-vaccine misinformation has been one reason vaccination rates have plummeted and global measles cases have surged. This year, the United States has had 1,250 cases of measles, the most since 1992.

Measles is not a harmless illness, as some anti-vaccine activists falsely claim, but one with deadly consequences.

“The big thing we show here is that even if a child gets through measles … you’re setting your kid up to be at increased risk to all these other infectious diseases that they could encounter on any given day,” said Michael Mina, an infectious disease epidemiologist at Harvard’s T.H. Chan School of Public Health and lead author of the first study, published in Science.

More than 7 million people are estimated to have been infected with measles in 2018. Coverage with measles, mumps, rubella vaccine would prevent more than 120,000 deaths directly attributed to measles this year, and it could “avert potentially hundreds of thousands of additional deaths attributable to the last damage to the immune system,” the authors wrote.

Mina and investigators from Harvard Medical School, Brigham and Women’s Hospital, analyzed blood samples of 77 unvaccinated children before and two months after a measles outbreak in 2013 in their Netherlands community. They found measles infection wiped out 11% to 73% of different antibodies that “remember” past encounters with germs and help the body avoid repeat bouts of influenza, herpes virus, pneumonia and skin infections. No loss of antibodies was observed in children vaccinated against measles, mumps and rubella.

Mina and his colleagues found that those who survive measles gradually regain immunity to other viruses and bacteria as they get re-exposed to them. But it may take months to years. In the meantime, people remain susceptible to complications of those infections, he said.

A second study, in the journal Science Immunology, analyzed the antibodies collected from blood samples of 26 children from the same group of unvaccinated Dutch children. Researchers from the Wellcome Sanger Institute, University of Amsterdam and their collaborators sequenced their antibody genes and found that specific immune memory cells were no longer in the blood of two children after measles illness.

Past studies suggested that measles virus wipes out a significant portion of essential immune memory cells that protect the body against infectious diseases. The new findings are the first to measure how that damage occurs.