Millions of people around the world get vaccinated every year with no ill effects. The most likely reactions tend to be minor and temporary, like redness around the injection area or a fever.
Serious problems — deafness, seizures or brain damage — are so rare that the federal Centers for Disease Control and Prevention reports that it is uncertain if they can even be linked to the shots.
“It’s like if 1 million people got a vaccine, and one walked out and got hit by a bus,” said Eben Kenah, an assistant professor of biostatistics at University of Florida. “It’s going to be very hard” to prove any connection.
The CDC puts the odds of a serious reaction like slipping into a coma at less than 1 in a million for the measles, mumps and rubella vaccine. And public health experts agree that any link between vaccines and autism — a connection made by a single research paper long since withdrawn — has been thoroughly debunked.
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Yet a small but increasing number of parents chose to opt out of vaccines, a choice experts say only exposes their children to considerably higher risks.
“The benefits far outweigh the risks,” said Dr. Aileen Marty, a professor of infectious diseases at Florida International University. “I know people have individual rights, but unfortunately there’s an awful lot of bad information about these vaccines out there, and people are not thinking about the fact that one out of every five kids is going to have a complication from the measles.”
About one in five children who get the chickenpox vaccine will experience swelling near the needle mark. One in four will get a fever after being vaccinated with the Diphtheria, Tetanus, and acellular Pertussis shot.
The ramification of contracting the illnesses are far more serious. For example, 1.6 percent of babies who contract whooping cough will die and 23 percent will develop pneumonia, according to the CDC. Among children who contract measles, one of every 1,000 will develop brain swelling that can cause deafness or mental retardation.
Still, some parents worry about reactions to preservatives and other substances added to vaccines. One called Thimerosal, which contains mercury and is used to prevent bacteria growth, was once widely used and deemed safe by numerous studies. But it was removed from all vaccines except for some flu shots in 2001.
Some shots also include dyes and antibiotics that might trigger allergic reactions. Lisa Joyce Goes, who co-founded an activist group called Thinking Moms Revolution, want potential allergic reactions to be considered before kids are given shots.
“Because the science is extraordinarily complex, what we’re saying is these children need to be tested before,” she said. “I’m not anti-vaccine. I’m pro-informed consent.”
An earlier version of this story gave an incorrect title for Dr. Aileen Marty.
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