By Brenda Goodman, MA
WebMD Health News
Reviewed by Hansa D. Bhargava, MD
Feb. 10, 2015 -- As measles creeps across the U.S., public health officials have urged everyone to get vaccinated against the highly contagious disease.
Some have questioned that advice, though, finding new reasons to fear the MMR shot, which protects against measles, mumps, and rubella.
In the late 1990s, parents turned away from the MMR vaccine in droves because of an infamous and now discredited study linking the vaccine to autism. Since then, dozens of medical studies have shown there's no such link. In perhaps the surest sign of this myth's demise, the advocacy group Autism Speaks has joined the chorus of experts urging parents to vaccinate their kids.
But there are new concerns that seem to have emerged on social media in the wake of the latest outbreak.
No. 1: The Vaccine Doesn't Work Because It Protects Against a Different Strain
The first concern, which has been posted on anti-vaccination blogs, is that the vaccine protects against an "A" type of measles virus, while the kind that's making everyone sick is a "B"-type virus. Therefore, the vaccine doesn't protect against the kind of measles that's making everyone sick.
This idea is based in some truth, but it's wrong.
There are different strains of measles virus. Each is given a letter and a number, for example B3 or D4. They refer to the genetic fingerprint of the virus. Since 1990, 19 different strains, or fingerprints, have been identified, according to the CDC, and scientists use these fingerprints to link infections during an outbreak.
It's also true that the vaccine protects against an "A" strain of the measles, while the strain going around in at least nine cases of this outbreak has been B3.
But here's where some people seem to be confusing the measles with the flu. With seasonal flu, the virus changes so much that they have to tweak the vaccine recipe each year in an attempt to alert the immune system to the circulating strain.
The measles virus doesn't change as much. So showing the immune system one type of it through the vaccine is enough to protect the body against all types.
"The measles vaccine protects against all strains of measles," says Andrea Berry, MD. She's an assistant professor at the University of Maryland's Center for Vaccine Development, in Baltimore.
No. 2: It's Vaccinated People Who Are Spreading Measles, Not Those Who Are Unvaccinated
This is another idea discussed on social media and blogs. It says the measles shot, which contains a weakened but live form of the virus, can give people infections that allow them to pass on the disease to others.
Not exactly, says William Schaffner, MD. He's an infectious disease specialist at Vanderbilt University in Nashville, TN.
"The vaccine virus, can, on occasion, spread to others," Schaffner says. "That gives them protection. It doesn't give them disease."
But, he says, to be clear: "On occasion" means the possibility is so remote that it's highly unlikely.
If it did happen, he says, it would be a good thing, since the person who "caught" the vaccine virus would get protection, but no illness. They probably wouldn't even know it had happened.
Other experts say these kinds of infections are so rare that they're more of theory-based than anything else.
Bettina Bankamp, PhD, a microbiologist at the CDC, says the agency is not aware of any cases where recently vaccinated people have spread the disease.
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