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.