From a first cough to weeks quarantined alone in bed,...

The coronavirus continued to upend daily life in America Monday, as schools closed, public spaces emptied and entire cities were placed on lockdown.

In an effort to staunch the outbreak, the White House urged Americans to isolate themselves and avoid groups of more than 10 people as part of a campaign called “15 days to slow the spread.”

“We will rally together as one nation and we will defeat the virus,” President Trump said. “We can turn the corner and turn it quickly.”

Get the latest developments on the coronavirus straight to your inbox by signing up for our special edition newsletter.

Here’s what else we learned today:

States team up:

In an unheard-of accord between three states, Govs. Andrew Cuomo of New York, Phil Murphy of New Jersey and Ned Lamont of Connecticut agreed to shutter businesses — including gyms, movie theaters and casinos — beginning at 8 p.m. tonight and banned gatherings of more than 50 people. All bars and restaurants will be open for takeout only.

Murphy also announced a loose curfew in the Garden State, tweeting that he “strongly discouraged” all non-essential travel between 8 p.m. and 5 a.m. going forward.

But New York City Mayor Bill De Blasio just couldn’t stay away from the gym.

Moving toward a vaccine:

Scientists kicked off testing the first experimental coronavirus vaccine on human volunteers Monday, administering a shot that was a milestone in the race to protect the world from the pandemic.

However, officials warned it could take a year to 18 months to fully test and approve any vaccine.

No, Canada:

Canadian Prime Minister Justin Trudeau says he will close the country’s borders to anyone who isn’t a citizen or a permanent resident. US citizens are exempted — for now. Trudeau is self-isolating at home after his wife, Sophie, tested positive for the virus.

More stars affected:

Idris Elba announced he tested positive for the coronavirus.

Arnold Schwarzenegger is urging the elderly to self-isolate, just like he is — with the help of his mini ponies.

“Today’s” Al Roker and Craig Melvin are taking time off after a colleague on the third hour of the show contracted coronavirus.

Stocks take a tumble:

In another bad day for US stocks, the Dow plunged nearly 3,000 points — or nearly 13 percent, its biggest drop since the “Black Monday” crash of 1987 — after the Federal Reserve’s surprise move to slash interest rates stoked fears about the damage the coronavirus is doing to the economy.

San Fran in lockdown: