When my daughter, Elena, was 6 months old, we took her in for her regularly scheduled booster vaccinations. Her father and I had never questioned immunizations. We believe in herd immunity and the power of evidence-based medicine. Immunizations were a no-brainer.

Elena was usually a happy, contented baby, but a few hours later, she was stiff in my arms and would not stop crying. Finally, exhausted, she fell asleep. We went to bed thinking it would be over in the morning. But in the middle of the night, we heard odd sounds coming from Elena's room. Her father stumbled into her room and found her seizing in her crib, her tiny limbs flailing out of control and her face contorting.

Elena had suffered a tonic-clonic seizure, a known side effect of the diphtheria, tetanus and pertussis immunization, the pertussis (whooping cough) portion in particular. She was indeed fine the next day, but for her parents, it was a terrifying experience.

Elena went on to suffer almost a dozen seizures over the next couple of years, each one exhausting to her and terrifying to us. The seizures were not what are known as febrile seizures — caused by a high fever. Rather, they were idiopathic — no known explanation. For several years, we dosed her twice a day with anti-seizure medication to keep her overly active brain under control.

The neurologists told us it was just a coincidence — that the immunization had not caused this seizure disorder, although the first seizure was certainly correlated with the immunization. Nonetheless, our family doctor respected our choice when we declined the scheduled 18-month pertussis booster.

About a year later, when Elena was almost 3, she came down with what we thought was a regular virus. She developed a cough, which got worse over several weeks. It seemed as if she could not stop coughing, and when she coughed, she sounded like she was going to choke to death. She produced huge mucous bubbles from her nose and mouth, like nothing I'd ever seen, and I was again often terrified in the middle of the night — this time that she couldn't breathe and that there was nothing I could do to help her. Once she stopped coughing long enough to look at me tearfully and say, "I sound like a crow!"

It turned out she had pertussis. Not only did she have it, but her 14-year-old baby-sitter caught pertussis from her and was sick for months. (Current research shows that pertussis vaccination immunity often does not last into adulthood.) We will never know who else she infected.

Elena coughed for probably a year. Because of the damage to her airways, she required multiple nebulized medication treatments every day. When she caught regular viruses, as kids do, she coughed, often painfully, for weeks. We made multiple visits to the ER when I was afraid she couldn't breathe.

When Elena had seizures, I spent a lot of time feeling foolish that we hadn't done better research, asked more questions and made a more considered decision before vaccinating her. We had just accepted that vaccinations were the right thing to do.

But when Elena had pertussis, I spent a lot of time feeling foolish that I had flat-out rejected the booster vaccine because of my fear of the side effects. I also regretted that we were responsible for infecting others in our community with a difficult disease that can have serious consequences.

I can't say which was worse — experiencing a known vaccine side effect or experiencing the disease itself. Both were terrible.

As a parent, any time your child is at risk or suffering, you struggle with your choices. My heart goes out to children who have suffered lasting consequences from immunizations and to their parents, who are only trying to make good choices for their children.

But we can't lose sight of the fact that immunizations protect us from dangerous diseases — diseases that have serious consequences, for our own children and for others. Parents must recognize that those consequences can and may happen to their own children, and many others, when they decline to vaccinate.

Mary Dunnewold lives in Northfield.