The seven-day average for COVID-19 hospitalizations and deaths in the United States has been declining, according to data compiled by The COVID Tracking Project, a volunteer-run effort to track the U.S. outbreak.

The country's seven-day average for COVID-19 hospitalizations was 96,534 on Wednesday, the data shows.

With the exception of Vermont, all U.S. states and territories have seen either declines or no changes in their seven-day COVID-19 hospitalization rates, according to The COVID Tracking Project.

The country's seven-day average for COVID-19 fatalities was 3,039 on Wednesday, the data shows.

"We have seen the 7-day average for new deaths decrease for over a week," The COVID Tracking Project wrote on Twitter. "At the same time, states are reporting an average of 3,000 people dying per day. The data is hopeful and devastating."

All Australian Open events were canceled Thursday after a hotel worker tested positive for COVID-19, organizers said.

All tournament personnel and players are undergoing testing and isolating in their hotel rooms until they get a negative result, according to Tennis Australia, the organizers of the annual tennis tournament.

"We will work with everyone involved to facilitate testing as quickly as possible," Tennis Australia said in a statement Thursday.

Organizers did not say how many of the athletes staying at the Grand Hyatt Melbourne would be affected.

This is the second COVID-19 incident to derail the Australian Open after passengers on a special charter flight bringing professional tennis players to Australia also tested positive for the virus. That incident caused a number of players to be confined to their hotel rooms for two weeks.

ABC News' Zoe Magee contributed to this report.

The number of people in the United States who have received their first dose of a COVID-19 vaccine reached 27.1 million on Tuesday, surpassing the country's cumulative number of confirmed COVID-19 cases to date, according to a report from the U.S. Department of Health and Human Services.

In total, 8% of the U.S. population has received one or more vaccine doses.

Just over 26.5 million people have tested positive for COVID-19 in the U.S. since the start of the pandemic, according to data complied by Johns Hopkins University.

ABC News' Josh Margolin and Brian Hartman contributed to this report.

Despite older people being more likely to suffer severe illness or death, individuals between the ages of 20 and 49 were the ones responsible for 72.2% of COVID-19 spread in the United States last year, according to a new study from researchers at England's Imperial College London.

The study, which was published Tuesday by Science, the peer-reviewed academic journal of the American Association for the Advancement of Science, also found that adults aged 35 to 49 were responsible for more than 41% of spread in the U.S. in 2020. Imperial College London researchers believe this was not the result of schools reopening, but more likely because of the amount of movement in the community.

Less than 5% of COVID-19 cases in the U.S. originated from children aged 9 and under, while less than 10% originated from kids aged 10 to 19, according to the study.

ABC News’ Eric Strauss contributed to this report.

An accommodation facility for refugees in the German city of Cologne has been hit by new, more contagious variants of the novel coronavirus, city officials said.

At least 41 residents of the Herkulesstrasse facility have tested positive for COVID-19. Variants first identified in South Africa or Brazil have been detected in 31 of them so far, according to a statement from the city government on Sunday.

At least 16 staff members at the facility have also tested positive for COVID-19, with the South Africa variant detected in 11 of them so far. Variant analysis is still pending on the other five, according to the statement.

All residents of the facility have been under quarantine since Friday, while the site has been under surveillance since Sunday. Entry into the refugee accommodation center, which can house up to 600 people, is currently banned, according to the statement.

The first known COVID-19 cases were confirmed among two employees at the facility about 10 days ago, while the first case of a variant was confirmed last week, according to the statement.

Dr. Harald Rau, head of Cologne's public health department, said the detection of variants at the refugee accommodation center "is a clear alarm signal for all of us."

"I ask all people in Cologne to avoid contact even more consistently than before and to follow the distance and hygiene rules of infection protection," Rau said in a statement Sunday.