The Sabrina the Teenage Witch star, 45, shared last Wednesday that she had likely gotten COVID-19 from her eldest son, Mason Walter, 15, whom she thinks contracted the virus at school.
By Sunday, Hart said she was "doing so much better."
"I'm just sending an update because so many people have been checking on me," the actress said in an Instagram video. "I want to let you know that I'm doing so much better. I feel like I'm probably at like 75%; at the last video I was probably like 20-25%."
"It's been a rough week, but I'm feeling better; Mason's feeling better."
Hart said, though, that her youngest son Tucker McFadden, 8, has since tested positive.
Hart said she's continuing to rest, away from her family.
"I'm staying very isolated and separate, and just wanted to send love to everybody out there," she said. "Thanks for checking on us, thanks for all the chicken soup. I really felt the outpouring of love, and I just want to thank you. Stay safe everybody."
RELATED GALLERY: Celebrities Who've Tested Positive for COVID in 2021
Hart said last week that she had a breakthrough COVID-19 case after being fully vaccinated, and expressed her frustration with the lack of a mask mandate at schools in her home state of Tennessee.
"I think as a country we got a little lazy and I'm really mad that my kids didn't have to wear a mask at school. I'm pretty sure where this came from," she said.
Breakthrough cases — COVID-19 infections that occur in people who have been fully vaccinated against the virus — are rare, but possible and expected, as the vaccines are not 100% effective in preventing infections. Still, vaccinated people who test positive will likely be asymptomatic or experience a far milder illness than if they were not vaccinated. The majority of deaths from COVID-19, around 98 to 99%, are in unvaccinated people.
RELATED VIDEO: Melissa Joan Hart Contracts Breakthrough COVID
Hart said last week that she was "scared and sad, and disappointed in myself and some of our leaders."
"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," she added of the ongoing pandemic. "I hoped it was, but it's not, so stay vigilant and stay safe."
As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.