The Rev Jesse Jackson is being treated for Covid-19.
The civil rights leader, 79, has been hospitalized with the virus despite already receiving both doses of the Pfizer vaccine.
His wife, Jacqueline, has also tested positive.
According to their son, Jonathan Jackson, the couple are being treated at Northwestern Memorial Hospital in Chicago, Illinois.
He told the ABC7 news network that his mother had been "real lethargic" before being diagnosed.
In a statement over the weekend he said that both his parents were "resting comfortably" in hospital and "responding positively to treatments".
Although his mother, 77, is receiving oxygen, Jonathan said she was managing to breathe on her own without the aid of a respirator.
"Nothing severe. Because of her age and her current health, it is more challenging," he told ABC7.
In a statement on Monday, he asked people to pray for his parents.
"We are ever mindful that COVID-19 is a serious disease and we ask that you continue in prayer for my parents, as we remain prayerful for yours," he said.
Senator Bernie Sanders is among the well-wishers.
"The Rev. Jesse Jackson has been one of the great leaders of our time in the fight for racial, social and economic justice. He and his wife, Jacqueline, have been hospitalized with COVID-19. Jane and I and all Americans wish them a full and speedy recovery," he said.
Civil rights activist Al Sharpton tweeted: "Let us all pray for Rev. and Mrs Jesse Jackson. They need our sincere and intense prayers. Prayer changes things!!!"