December has been the worst month on record for cases, hospitalizations, and deaths. Even with delays in reporting because of the holidays, hundreds of thousands of Americans are still testing positive for the virus every day.

The U.S. has logged more than 5.6 million cases in the first 28 days of December -- more than any month on record, according to ABC News’ analysis of data compiled by the COVID Tracking Project.

According to the CDC, California currently has the highest average of daily cases per 100,000 people in the last seven days, followed by Tennessee, Oklahoma and Arizona.

Across the U.S., 121,235 people are currently hospitalized with COVID-19 -- setting a new record high since the pandemic began. That total is double the previous hospitalization peaks from April and July.

ABC News’ Arielle Mitropoulos contributed to this report.

Vice President-elect Kamala Harris received her first dose of the Moderna vaccine on Tuesday morning at United Medical Center in Washington, D.C.

"That was easy!" she said after. "I barely felt it."

"I want to encourage everyone to get the vaccine," Harris said. "It is literally about saving lives. I trust the scientists, and it is the scientists who created and approved this vaccine."

"Right in your community is where you can take the vaccine," Harris said. "Where you will receive the vaccine by folks you may know, folks who otherwise are working in the same hospital where your children were born, folks who are working in the same hospital where an elderly relative received the kind of care that they needed. So I want to remind people that they have trusted sources of health, and that's where they will be able to go to get the vaccine, so I encourage them to do that."

Harris’ husband, Doug Emhoff, also received the vaccine.

Staff and residents of Holyoke Soldiers' Home in Holyoke, Massachusetts, started receiving COVID-19 vaccinations Tuesday morning.

Staff looked on as the first person -- 78-year-old man U.S. Air Force Veteran Robert Aucoin -- was inoculated.

The long-term care facility has suffered one of the worst coronavirus outbreaks in the country. In the spring, 76 veterans who lived at the home died of the virus. A resident who had been living in an off-site nursing facility since April died earlier this month.

Two former top administrators pleaded not guilty to criminal negligence charges connected to the residents' deaths, WCVB reported.

U.S. states have begun vaccinating patients at long-term care facilities in an effort to keep the most vulnerable Americans safe from the virus. The government's goal is to have 20 million Americans vaccinated by the end of the year.

The TSA screened 1,111,751 travelers at checkpoints across the U.S. on Monday. This marked the seventh day within the last 11 days that more than 1 million people were traveling.

ABC News’ Sam Sweeney contributed to this report.

The Centers for Disease Control and Prevention updated its guidelines for people with underlying health conditions planning to take a COVID-19 vaccine.

They CDC said that adults with underlying medical conditions -- who are more at risk of becoming seriously ill from COVID-19 -- can receive a vaccine against the virus as long as they have not had a severe allergic reaction to any of the ingredients in it.

The new guidelines state that people with HIV and those with weakened immune systems due to other illnesses or medication should be aware that information about the safety of COVID-19 vaccines for their group is not yet available. While people with HIV were included in clinical trials, more data is required to provide safety guidelines regarding the effects a vaccine could have on them. The same is true for people with autoimmune conditions.

People who have previously had Guillain-Barre syndrome or Bell’s palsy may receive a COVID-19 vaccine, though experts are still acquiring more data about their groups as well.

The CDC added that people should continue to follow coronavirus health measures -- such as wearing a mask and staying 6 feet away from others -- after receiving the shot, as experts have more to learn about the protection that COVID-19 vaccines provide under real-life conditions.