Children who catch measles are more vulnerable to other serious infections for the next two to three years, experts have warned.
Scientists believe the disease, which is seeing a resurgence across the UK, wipes out a child’s immunity to other illnesses.
After surviving measles, children may fall ill or die from other infections which they previously had immunity to, they said.
The findings would help explain the mysterious large drops in mortality of up to 50 per cent following the introduction of measles vaccinations, the researchers said.
Prior to vaccines, measles was usually associated with much less than 50 per cent of childhood deaths.
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Assistant Professor Michael Mina, from Harvard Medical School in Boston, who led the new research, told the PA news agency that unvaccinated children who got measles were at greater risk from a range of potentially deadly infections such as pneumococcal infections, which include meningitis, septicaemia and pneumonia, serious respiratory viruses and a range of bacterial pathogens.
He added: “With the hypothesis that we have – which we believe is true – measles would cause this amnesia in your immune system that would affect your whole immune response.
“Measles takes somebody’s more mature immune response and it brings them back a few years – it brings them back to a more naive immunological state.
“When you get those infections, they might not be worse than the first time you got them, but it’s like resetting your immune system so it thinks it has not seen this pathogen before.
“Children are the most vulnerable in the first few years of life because their system hasn’t had the opportunity yet to develop memory of what is a danger and what is not a danger.
“It could be like repeating the first few years of life again when looking at some of these pathogens.”
Dr Mina said measles was like a “master infection”.
“Even if you get all the other vaccines but not MMR, if the child gets measles it could negate the effect of some of those vaccines, such as diphtheria, pertussis (whooping cough), rotavirus or the pneumococcal vaccine.
“Vaccines are like accelerated educations for the immune system.
“You can take a 1.5 year old and give them lessons about all these pathogens which, previous to vaccines, they would have slowly got exposed to at their own peril.
“It’s so important to vaccinate children.”
The research comes after the UK lost its “measles-free” status due to a rise in the number of cases being seen across the country.
Prime Minister Boris Johnson has called for health leaders to renew their efforts to ensure 95 per cent of the population have had both doses of the MMR vaccine.
The Government is concerned about the rise of anti-vaccination messages on social media and their influence on parents who go on to shun vaccines.
Currently only 87.2 per cent of children have had the second dose of the jab, down from a high of 88.6 per cent in 2014-15.
There were 532 confirmed cases of measles in the UK during the first six months of 2019, and more than 2,400 cases from January 2016 to June 2019.
Across the globe in 2018, measles killed about one in every 75 infected children, leading to more than 100,000 deaths.
Professor Mina will present his findings at the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) vaccine conference in Bilbao, Spain.
His team’s observations have been backed by numerous studies which show that the measles virus infects a large proportion of the “memory cells” of the immune system.
This results in so called “immune-amnesia”, which means the immune system cannot remember some of the diseases it has fought in the past.
This leaves children exposed to the risk of re-infection with such diseases.
A UK study on more than 2,200 children with measles found they were 24 per cent more likely to need antibiotics in the five years after suffering measles than children who never had the disease.
They were also more likely to suffer a range of infections, including chest infections, viral illnesses and tonsillitis.
Dr Jamie Lopez Bernal, consultant epidemiologist for immunisation at Public Health England, said: “These findings only add to the evidence of the phenomenal impact of vaccination programmes.
“No other medical intervention has been as important in the last 50 years.
“UK measles vaccination has prevented 20 million cases and 4,500 deaths – and that’s not taking into account the potential other benefits.
“This is about not only protecting ourselves but protecting each other.
“Vaccines stop the spread of disease and save lives.”
Helen Johnson, from the European Centre for Disease Prevention and Control, said: “It is tragic and unacceptable that children and adults continue to die from complications of measles, when safe and effective vaccines are readily available.”