The measles outbreak that started at Disneyland in San Diego, Calif. has quickly spread from 9 to 51 cases in a matter of weeks — leading to several unvaccinated teenagers at a high school being sent home for an undetermined amount of time.

Amidst the backlash against the parents of unvaccinated students, one student’s mother, Michelle Renfro, is explaining why her 15-year-old daughter Rebecca wasn’t vaccinated: it wasn’t because she was scared of her daughter getting autism or other debunked Anti-Vaxxer claims. Instead, it had to do with the risk of Rebecca being severely allergic to the vaccine.

Rebecca was vaccinated against all other diseases except measles — only because her older brother had suffered a severe allergic reaction to the measles vaccine. The doctor told Renfro to avoid vaccinating her daughter for the same reason. Less than 1 in a million doses of Measles, Mumps, and Rubella (MMR) vaccine causes allergic reactions.

“I’ve seen the news. I’ve seen how angry some of the parents are with people who don’t get vaccinated, going so far as to say, ‘This is all because of 24 sets of stupid parents,’” Renfro told Today.com. “I didn’t get a choice as to whether or not Rebecca got this shot,” “My only choice was: do I want to risk my daughter’s safety? I’m not opposed to having her vaccinated, if I knew she safely can have it.”

Rebecca was one of 24 unvaccinated Huntington Beach High School students who have been barred from going to school until January 29th, because they were exposed to a classmate with measles and could potentially have gotten infected. Officials at the Centers for Disease Control and Prevention (CDC) advised Renfro to keep her daughter quarantined for 21 days, during which the virus could be incubating.

Currently, California health officials are warning people to stay away from Disneyland — where the current measles outbreak originated — unless they’ve been vaccinated. It’s likely that the outbreak could get worse before it improves, and if that’s the case, Rebecca and her other classmates might be quarantined for longer than they thought. If anything, the situation is just another reminder to vaccinate your kids — unless, of course, there’s a severe life-threatening issue like an allergic reaction.

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