Joe Biden tested positive for coronavirus on Thursday morning, the White House revealed, just hours after returning from a trip to Massachusetts.

The White House said Biden, age 79, is only experiencing “very mild symptoms” and is fully vaccinated and boosted with four shots of the Pfizer coronavirus vaccine.

The president’s last negative coronavirus test was Tuesday, the White House revealed, indicating it is possible he was positive during his trip to Massachusetts on Wednesday.

Biden was not seen wearing a mask in public during his trip, as he met and traveled with Massachusetts officials to deliver a speech warning of the dangers of climate change. He also spent time shaking hands and greeting Democrat officials and supporters after his speech. Massachusetts Sens. Ed Markey and Elizabeth Warren attended the event as well as Biden’s climate czar John Kerry and his climate advisor Gina McCarthy.

On Saturday evening, the president returned from travel in the Middle East, which included visits to Saudi Arabia and Israel where he personally greeted public officials and did not wear a mask in public settings. On Tuesday, Biden met with the first lady of Ukraine Olena Zelenska at the White House.

White House doctor Dr. Kevin O’Connor revealed in a letter that Biden has a runny nose, a cough, and is experiencing “fatigue” and that his symptoms began “yesterday evening.”

Biden will undergo treatment of the antiviral therapy treatment Paxlovid, according to the White House, as he recovers from the virus.

Officials stressed Biden would continue to hold meetings at the White House via phone and video conferencing through Zoom, despite his illness.

“Consistent with CDC guidelines, he will isolate at the White House and will continue to carry out all of his duties fully during that time,” the White House said,

Biden was scheduled to leave for a trip to Pennsylvania on Thursday where he planned to deliver a speech about crime and gun control and participate in a fundraiser later Thursday evening before traveling to his home in Delaware. Those events have been canceled.

The president will “continue to work in isolation until he tests negative” the White House said.