A Mount Sinai study published Wednesday in the journal "Science" found that most people who experienced mild-to-moderate COVID-19 symptoms have "a robust antibody response" that kills the virus and is "relatively stable for at least five months."

"While some reports have come out saying antibodies to this virus go away quickly, we have found just the opposite -- that more than 90 percent of people who were mildly or moderately ill produce an antibody response strong enough to neutralize the virus, and the response is maintained for many months," Florian Krammer, a senior author of the paper and a professor of vaccinology at the Icahn School of Medicine at Mount Sinai, said in a statement.

"Determining the duration and levels of antibody that protect us from reinfection" is "essential for effective vaccine development," Krammer added.

The study included data from 30,082 people.

French President Emmanuel Macron announced a partial lockdown on Wednesday.

Bars and restaurants will be closed and private and public gatherings will be prohibited nationwide.

Permission slips will be required for outings, but schools and various public institutions and factories will remain open.

The restrictions, which will be reviewed every 15 days, go into effect Thursday night and will last through at least Dec. 1.

Macron's announcement follows an alarming spike in deaths from the virus as in addition to record numbers of new cases across France.

"The virus is circulating in France at a speed that even the most pessimistic forecasts had not predicted," Macron said. "If we do not put the brakes on hard today our hospitals will be overwhelmed."

On Tuesday, France lost 527 lives to COVID-19, Macron said. As of Wednesday, the nation's positivity rate was 18.6%.

France's public health agency has confirmed over 1,198,000 cases and 35,541 deaths.

ABC News' Ibtissem Guenfoud and Christine Theodorou contributed to this report.

Major League Baseball criticized Justin Turner for returning to the field Tuesday night when his team won the World Series after the Dodgers' third baseman was removed from the game because he tested positive for COVID-19.

Turner was put into isolation, according to a statement from MLB, but he "chose to disregard the agreed-upon joint protocols and the instructions he was given regarding the safety and protection of others."

"Turner’s decision to leave isolation and enter the field was wrong and put everyone he came in contact with at risk," MLB said. "When MLB Security raised the matter of being on the field with Turner, he emphatically refused to comply."

The Commissioner’s Office is investigating.

The Dodgers were tested Tuesday night, and both the Rays and Dodgers were tested again Wednesday, MLB said, adding that the teams' "travel back to their home cities will be determined after being approved by the appropriate authorities."

The Dodgers said Wednesday that the team will wait to celebrate with the fans "until it is safe to do so."

The Boston Marathon set for April 2021 will be postponed until at least the fall of 2021, the Boston Athletic Association announced Wednesday.

The postponement comes amid a rise of coronavirus cases in Massachusetts. This year's marathon was canceled.

Monday marked the state’s highest daily case count since the spring, the Boston Herald reported. Last week brought multiple days of daily case counts over 1,000, which the state hadn’t seen since the spring, the Herald said.

Massachusetts now has over 149,000 confirmed COVID-19 cases and at least 9,664 fatalities.

ABC News’ Leo Mayorga contributed to this report.