Ariel Loop is a registered nurse who lives in Pasadena, California, with her husband and two kids, Mobius, age four, and Penrose, age two. In 2015 Loop and her husband took four-month-old Mobius—then their only child—to Disneyland, where they believe he caught the measles. SELF asked Loop to tell us the story of Mobius getting sick, his recovery, and what it’s like to realize your child has contracted a vaccine-preventable illness.

And just for some background so that you can wrap your mind around Loop’s story, here’s how things work when it comes to how and when babies and children should be vaccinated, according to the Centers for Disease Control and Prevention (CDC): Parents are encouraged to follow the CDC’s recommended immunization schedule. Following the schedule, babies should be vaccinated against hepatitis B at birth and at two months are vaccinated against illnesses like rotavirus, diphtheria, and polio. Under the schedule, children typically don’t receive their first dose of the measles, mumps, and rubella (MMR) vaccine until 12 months of age. The second dose of the vaccine doesn’t come until at least age four. Waiting until your child is even partially vaccinated against measles to take them into a crowded place is understandably tricky, if not impossible. (Not to mention endemic cases of the disease were declared eradicated in the Americas in 2016.)

Disneyland has always been a special place for me and my husband, Chris. We got married there and we announced both of our pregnancies there. As we're residents of Pasadena, California, Disneyland isn’t far away and it’s not uncommon for people to get annual passes. For us, a trip to Disneyland is kind of like going to the local park for other people.

During my pregnancy with my son Mobius, I regularly went to Disneyland and walked the park. So it felt inevitable that we would take him there after he was born. Chris and I waited a while to do that, though, and we did everything during Mobius’s first few months of life that we could to keep him safe. We didn’t take him out until a few weeks after his two-month vaccines, and we made sure everyone who was in contact with him before then was healthy and up-to-date on their vaccinations. I felt like we were doing everything within reason to keep him safe.

Once Mobius had his two-month shots, we decided to take him to Disneyland. I knew what his two-month shots protected against, and I wasn’t under any illusion that they would protect him against measles. But I also didn’t think that was something we needed to worry about. At the time I was more concerned with things like whooping cough than anything. And Mobius loved the park. He looked at the lights and we took family photos. We loved getting to introduce him to a place that held so much meaning for our family.

We made another trip to Disneyland with Mobius when he was four months old and it was a great time. Measles outbreaks were in the news about two weeks before our visit, including measles cases linked to Disneyland. However, by the time we went there were no reports I was aware of [about] current transmissions at the park. I asked my pediatrician about the measles risk before we went and we were told that it was just as much a risk there as it was anywhere at that point because it’s so contagious. There was technically a measles risk to take Mobius even to the local supermarket, I remember being told. My thought was that he was about as protected as possible while out in the wild without an N95 mask. Unfortunately he was still exposed to measles during our visit—we just didn’t know it yet.