Photos from 1 year ago show how little the US understood about the pandemic to come

A study found that Mardi Gras "greatly accelerated" the coronavirus outbreak in New Orleans, Louisiana — and likely introduced the virus to other nearby states.

Though the research is still awaiting peer review, the authors wrote that most of the roughly 50,000 COVID-19 cases reported during Louisiana's first wave can likely be traced back to Mardi Gras.

Researchers at the NYU Grossman School of Medicine estimate that New York City's initial coronavirus outbreak started in mid-February. As late as March 9, New York City Mayor Bill de Blasio told people not to worry about transmission in crowded areas.

"It's not people in the stadium, it's not people in the big open area or a conference," de Blasio said that day, referring to the way the virus spreads.

Seven days later, de Blasio closed the city's public schools. Four days after that, Gov. Andrew Cuomo issued a statewide stay-at-home order.

That same day, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, called for a "dramatic" decline in personal interactions in bars and restaurants.

"Everybody has to take this seriously, even the young," Fauci told CNN.

A September CDC report found that adults with COVID-19 were twice as likely to have reported dining a restaurant in the two weeks before they got sick than those who tested negative.

Trump also falsely claimed on March 6 that anyone who wanted a coronavirus test could get one. But the US was only testing 20 out of every 1 million people at that point.

"We knew that this was coming, back as far as January," Biden told CNN on March 1.

He began canceling his rallies around March 10, shortly after the CDC advised older Americans to "stay home as much as possible" and avoid crowds.

Masks were in short supply in the spring, so US officials were primarily concerned with preserving enough for healthcare workers. That shortage, combined with limited research about whether face coverings were effective in curbing the coronavirus' spread, led experts not to recommend masks to the general public right away.

Instead, experts emphasized hand-washing and told people not to touch their faces, since preliminary research suggested the virus could spread via surfaces.

More recent studies have found, however, that surface transmission is somewhat rare. The virus spreads mainly when people share the same air — it travels either through respiratory droplets exchanged when an infected person coughs, sneezes, sings, talks, or breathes, or via smaller particles that linger in the air for minutes to hours.

Passengers waited in hours-long customs lines in cities like New York, Chicago, and Dallas/Fort Worth.

Chicago Mayor Lori Lightfoot told The Wall Street Journal that people were standing "cheek to jowl" at O'Hare International Airport. A passenger told the Journal that baggage claim there "looked like Ellis Island."

The NBA suspended its season on March 11 after several Utah Jazz players tested positive for COVID-19. The NHL, MLS, and National Lacrosse League followed suit a day later.

Sports stadiums have recently started to reopen at partial capacity. At the end of February, New York City began allowing 10% of seats to be filled in stadiums like Madison Square Garden and the Barclays Center.

The parks remain closed, but they could reopen as soon as April 1, according to California's guidelines. Capacity could range from 15% to 35%, depending on local transmission rates.

By then, New York's stay-at-home order had been in place for three days. The physical trading floor had never shut down independently before, even during World War II or 9/11.

At the same briefing, though, Fauci warned that "the worst is yet ahead."