Check yourself, public health officials say, as the number of cases in a Michigan measles outbreak climbed Friday by five more people to 39 cases — the largest statewide outbreak since 1991.

Even if you think you’ve been vaccinated for the measles, ask your doctor to check your immunization record to be sure.

If you have proof you received two doses of the measles, mumps, rubella vaccine (MMR), you should still ask to have the antibodies in your blood checked, especially if you’ve been to one of the growing number of exposure sites in Michigan.

Even if you had measles as a child or were born prior to 1957 and are considered immune by the U.S. Centers for Disease Control and Prevention, double check. And again, that’s especially true if you’ve been to a known exposure site.

There’s a chance you’re not as safe as you think you are.

“All these people walking around are vulnerable and don’t know it,” said Dr. Janet Snider, a Bingham Farms pediatrician. “We’re learning in the trenches because we don’t usually see measles,” which was pronounced eradicated in the United States in 2000 but is surging right now in pockets of the country.

“All those suppositions we have aren’t holding up,” she said. “It’s like you think your basement is waterproof if you live in the desert. But then all of a sudden there’s a flash flood, and then you really learn if it is.”

For many people born after 1957 but before 1989, they may have gotten only got one dose of the MMR vaccine, which might not be enough to protect them in an outbreak situation. The CDC changed its recommendations for the MMR vaccine in 1989, urging people to get two shots rather than just one, said Leigh-Anne Stafford, a spokeswoman for the Oakland County Health Division.

“For a lot of people who were born after 1957 but prior to 1989-1990, there was only one dose that was recommended at that time,” Stafford said. “A lot of people might feel they are up to date on their vaccines because their parents may say, ‘Oh, you’re up to date. We vaccinated you.’ But they’re not.

“So that’s why we keep talking about knowing your status. Are there two doses documented somewhere with a doctor? Or Is it listed in MICR (Michigan Care Improvement Registry), which is the Michigan registration database for immunizations? If you don’t, then get vaccinated.

Two doses of the MMR vaccine are believed to offer people up to 97% protection against measles, which is highly contagious and is spread by person-to-person contact and through the air, most often when an infected person coughs or sneezes.

Of the 39 confirmed Michigan cases, those infected with measles range in age from 8 months old to 63 years old. At least three of them had two documented doses of the MMR vaccine, according to the state Department of Health and Human Services. But at press time, the MDHHS did not know how many were unvaccinated or could not document their immunizations.

“The measles vaccine is safe and extremely effective,” Snider said. “Two doses confer 97% immunity to the population. But that still means that 3% of people may not respond to the vaccine.”

That means that if 100 vaccinated people are exposed to measles, three may catch it, she said. “But if 100 unvaccinated people are exposed to measles, 90 would likely contract it.

“People of all ages (should) check their vaccination status and make sure that they have had two documented MMRs after 1 year old, or they have had a blood test to confirm their immunity to measles.

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