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'We got lazy': Melissa Joan Hart reveals breakthrough COVID-19 diagnosis

Hart ended her video with a plea for people to continue to take precautions against the virus.

Television star Melissa Joan Hart said on Instagram that she had been diagnosed with a breakthrough case of COVID-19.

In the emotional video, the "Sabrina the Teenage Witch" actor expressed anger and disappointment and said that she had "gotten lazy" about following some precautions after being vaccinated.

"I'm mad, really mad," she said. "We tried and we took precautions and we cut our exposure by a lot but we got a little lazy, and I think as a county we got lazy."

New data collected by state health agencies shows that breakthrough infections among fully vaccinated people are incredibly rare. Of the 166 million people in the United States who are fully vaccinated against COVID-19, there are at least 248,943 breakthrough cases, according to the latest data that 42 state health agencies provided to NBC News.

While some states, like Pennsylvania and Missouri, did not provide total case numbers, state officials told NBC News that more severe outcomes among fully vaccinated people, including hospitalization and deaths, are highly unusual.

Hart said that she believed the virus had entered her home through her children's school and said that she thinks at least one of her children also has COVID-19. She is the mom of three boys: Tucker, 8, Braydon, 13, and Mason, 15. Hart did not disclose her older children's vaccination status.

"I'm really mad that my kids didn't have to wear masks at school," Hart said. "I'm pretty sure that's where this came from. Nothing I can do about it now. My little one, luckily, wore a mask every day, because he was so used to it from last year. He came home bragging every day 'Mom, I wore my mask,' and I was so thankful, and now if he does get it I can at least tell him he was a superhero to those in his classroom because he protected his teacher and his classmates from it."

Hart said that she herself was feeling "bad" after her diagnosis, and briefly described symptoms like a weight in her chest and difficulty breathing.

Hart said that she did worry about her husband, musician Mark Wilkerson, contracting COVID-19 in case she or one of her children did need to go to the hospital. Hart did not share Wilkerson's vaccination status.

"I just really hope my husband and the other (kids) don't get it because if someone has to be taken to the hospital I can't go with them," Hart said.

Hart ended her video with an emotional plea for people to continue to take precautions.

"I'm just scared and sad and disappointed in myself, in some of our leaders, and a lot of people, including myself," Hart said. "I just wish I'd done better, so I'm asking you guys to do better. Protect your families, protect your kids. It's not over yet. I hoped it was, but it's not. So stay vigilant, and stay safe."