Hillary Clinton tested positive for Covid-19 on Tuesday.
Clinton, 74, said she's experiencing mild cold symptoms and that her husband, former US president Bill Clinton, had tested negative.
"I'm more grateful than ever for the protection vaccines can provide against serious illness," the former secretary of state tweeted.
"Please get vaccinated and boosted if you haven’t already!"
Neither Hillary nor Bill, 75, had reported a positive Covid-19 test before Tuesday. Current White House press secretary Jen Psaki also tested positive Tuesday.
Last week, former president Barack Obama and current second gentleman Doug Emhoff both caught Covid-19.