Mom's measles immunity doesn't protect babies as long as thought
Doctors have known that mothers pass on measles immunity to their babies during pregnancy, leading to the belief that infants are protected against the disease for most of their first year of life. But a new study finds that most of this protection wanes much sooner than previously thought — within as little as three months.
Canadian researchers analyzed blood samples from almost 200 babies seen at a hospital in Toronto, looking for levels of protective antibodies to measles, which indicate immunity. They found insufficient levels in 20 percent of newborns, 92 percent of 3-month-olds and all of the 6-month-olds, according to the results, published Thursday in the journal Pediatrics.
“We were surprised with our findings,” said Shelly Bolotin, a scientist at Public Health Ontario and an assistant professor at the University of Toronto. “Prior to this research we assumed that in general, infants were immune to measles for at least the majority of the first 6 months of age.”
Previous research that looked at measles immunity in babies was done in communities where measles was more common, Bolotin told NBC News. The mothers in the new study were in Ontario, an area where there are high measles vaccination rates and people are not regularly exposed to the disease. These women, while likely still protected from vaccination, may nonetheless have lost some of their immunity because they were not regularly exposed to measles in the environment, which has the effect of boosting the immune system.
As a result, these mothers would not pass along as much immunity to their infants. “Low antibodies in mom means low antibodies in baby and then protection lasts less time,” Bolotin said.
This could leave babies vulnerable to measles infection for most of their infancy, until they are vaccinated starting at 12 months, she said, highlighting the importance of community-wide vaccination that provides “herd immunity” to the vulnerable infants.
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“There’s a really wide susceptibility gap between the time that the infants lose their protection and that time when babies get vaccinated,” Bolotin said. “So it really underscores the need to have everyone around this group protected because infants are at higher risk for complications of measles.”
The measles vaccine
In the United States, the measles vaccine, given as part of the measles, mumps and rubella (MMR) shot, is recommended from the ages of 12 months to 15 months and then again from 4 to 6.
While doctors may recommend a measles vaccine for babies as young as 6 months who will be traveling to areas where measles is circulating or who live in an area with an outbreak, currently it’s not warranted for all infants in the U.S. — where measles remains uncommon — to be immunized earlier, said Dr. Walter Orenstein, who co-authored an editorial that accompanied the new study.
“I don’t think there’s a call for doing anything different than we’re currently recommending,” said Orenstein, associate director of the Emory Vaccine Center and a professor of medicine, pediatrics and global health at Emory University in Atlanta.
But doctors and public health officials should continue to monitor this issue and possibly reconsider the advice if they see more measles cases in this young age group, he said.
It’s important to note that the measles vaccine is less effective in babies, particularly those under 6 months of age, Orenstein said, which is why the first dose typically is given at 12 months. Because the vaccine isn’t as effective in infants, those who do get it before 12 months still need to get the recommended two doses later on.
The MMR vaccine is not advised in pregnancy, so women of child-bearing age should make sure they’re immunized, Orenstein said.
Measles is a very contagious disease that typically causes a rash, high fever, runny nose, watery eyes and cough, and can lead to serious complications such as pneumonia, encephalitis and death. These risks are greatest for babies and young children.
A recent study found that measles also may have a lasting deleterious effect, wiping out the immune system’s “memory,” making people susceptible to diseases they previously had protection against.
Though measles was declared eradicated in the United States in 2000, there have been multiple outbreaks since then. So far this year, more than 1,200 cases of measles have been confirmed across the country, most of them in people who were not vaccinated against the disease, according to the Centers for Disease Control and Prevention.
Dr. Sean O’Leary, an associate professor of pediatrics at the University of Colorado in Aurora and a spokesperson for the American Academy of Pediatrics, said the new study offers more reason for all people to get their recommended measles vaccinations — to protect not only themselves but also others in the community who are at risk.
“The most important takeaway from this study is that if we maintain a highly vaccinated population then for parents of young infants essentially this is a nonissue,” O’Leary said.
Parents should make sure anyone around their babies, including day-care workers and other caregivers, is immunized, he advised.