Last week, our son Ox had an adverse reaction to the MMR vaccine.  I’m glad, and I’m grateful.

First, the downside. Ox came home from daycare with a fever hovering around 100° F/38° C. That’s high enough to worry first-time parents, and it was persistent. By Friday night he’d been feverish for days and couldn’t sleep. When we measured him at 103°/39°, we finally called the pediatric nurse hotline at the local children’s hospital. The nurse was cool, calm, confident, and knowledgeable, just as you expect a nurse to be. She listened to a first-time dad ramble on about his boy’s fever and then let us know that it sounded like a reaction to the MMR vaccine he’d had the week before.

It’s possible that he simply came down with a normal fever and the timing was a coincidence. A lot of reported adverse reactions to vaccines are coincidences. But his experience closely fits the profile of a known vaccine reaction.  Fevers are one of the most common adverse reactions to vaccines, affecting about ten percent of kids after their MMR shots. Our experience was worse than the typical fever; Ox spiked above the usual ceiling of 103° and it lasted a little longer than the standard two days.

Ox is fine today, but I don’t want to minimize the downside. Fevers can be dangerous, of course, leading to dehydration and other serious complications. And while Ox came through just fine, he suffered. He spent a few hot, cranky days unable to sleep or eat comfortably. That hit us, too. As new and first-time parents we don’t have a lot of perspective on what’s serious and what’s not; when the baby’s feverish for that long, it’s scary and upsetting. It also disrupts our lives; we’re very busy but Ox is our priority, so when he’s sick, it’s hard to keep all the other plates spinning efficiently.

But it’s good news, over all. Ox spiked a scary fever and spend a miserable few days waiting for it to break, and I’d have him do it again in a heartbeat. Because that fever is an indication that his immune system is responding to his MMR shot, which means he’s developing a powerful, natural immune response to dangerous diseases that could leave him deaf, sterile, or even dead.

Ox suffered an adverse reaction thanks to his pediatrician and the nurses, and I’m sincerely grateful for it. They gave him a shield against pathogens that evolved specifically to attack and ravage him, and that have seriously hurt unvaccinated kids in our community. And they helped make him into a shield in turn, protecting other children through communal immunity.

To Ox’s nurses and doctors and to all the doctors and nurses giving vaccines every day: thank you. You’re standing between our child and a world of suffering, and we’ll always be grateful—even when it causes a fever.