Health experts have been worrying about a third wave of COVID-19 hitting the U.S. after the holidays, as already 9 million people have traveled during the season. But speaking to "Good Morning America" Monday morning, Adm. Brett Giroir, the assistant secretary for health at the U.S. Department of Health and Human Services (HHS), said the country may not see another big spike in cases.

"How bad it will get really depends on what people do. After Thanksgiving, in the Midwest and the Northern Plains, we did not see a spike in cases, and in fact, it continued to go down," he said.

He added that while traveling does put people at higher risk of contracting the disease, we will not necessarily see another spike if people follow the rules.

"Limit travel if you can. If you're sick, please don't travel. Always wear a mask and watch your distance. And be careful, it's not really the travel, but it's mixing your bubble with a new bubble once you get there," Giroir said.

He added that this week, 4.7 million doses of a COVID-19 vaccine will be delivered to the U.S., getting the country closer to the government's goal of vaccinating 20 million Americans by the end of the year.

Adm. Brett Giroir, the assistant secretary for health at the U.S. Department of Health and Human Services (HHS) spoke to "Good Morning America" Monday morning to discuss the new coronavirus variant taking over the U.K.

"We don't have proof that it's here, but we do suspect that it is likely here, given the global interconnectedness," Giroir said. "We have no evidence that it's here. It's certainly not widespread here, but we need to look and make sure it's not here."

He added that while "there is increasing evidence that it really is more transmissible" or contagious, due to the viral load that people with that strain have been shown to have, there is "no evidence that it is more serious."

There is no evidence that people who become infected with the variant are more likely to be hospitalized or die, Giroir said.

"And we still believe -- don't have absolute proof -- but we have very good evidence and a good belief that the vaccines will still be effective," he added.

Huntington Hospital in Pasadena, California, released a patient information sheet documenting how they will use their medical resources should they see a shortage due to an overwhelming number of new patients following the holidays.

"We are not currently in this situation, but could be based on ongoing increase in hospitalized COVID-19 patients," they told ABC News, adding that on Sunday they had their highest number of patients (189) in a single day.

In the letter, the hospital explained that due to rising cases of COVID-19 in the community, they may experience limited resources. These include life support machines (like a ventilator or breathing machine), intensive care unit (ICU) beds and healthy medical staff to care for patients.

If there is a shortage of resources, a team of medical professionals will review the cases of all patients who are critically ill to determine how these resources should be shared throughout the hospital.

"If a patient becomes extremely sick and very unlikely to survive his/her illness (even with life-saving treatment) – limited medical resources may go to treat other patients who are more likely to survive," the letter reads.

"Our community is facing a public health emergency that has severely constricted the medical resources available to patients in the Los Angeles County and greater Southern California region. Hospitals such as ours are working hard to meet the dramatic rise in needed care during this COVID-19 surge. We expect to face additional challenges moving forward after the holiday season," the hospital said in a statement.

ABC News' Abigail Shalawylo 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.

A staggering 299,087 new cases of COVID-19 were confirmed in the United States on Saturday, according to a real-time count kept by Johns Hopkins University.

It's the highest tally of newly diagnosed COVID-19 infections that a country has recorded in a 24-hour reporting period since the start of the pandemic.

An additional 2,398 deaths from COVID-19 were also registered nationwide on Saturday, down from a peak of 3,750 on Dec. 30, according to Johns Hopkins data.

COVID-19 data may be skewed due to possible lags in reporting over the holidays followed by a potentially very large backlog.

A total of 20,430,088 people in the U.S. have been diagnosed with COVID-19 since the pandemic began, and at least 350,214 of them have died, according to Johns Hopkins data. The cases include people from all 50 U.S. states, Washington, D.C., and other U.S. territories as well as repatriated citizens.

Much of the country was under lockdown by the end of March as the first wave of pandemic hit. By May 20, all U.S. states had begun lifting stay-at-home orders and other restrictions put in place to curb the spread of the novel coronavirus. The day-to-day increase in the country's cases then hovered around 20,000 for a couple of weeks before shooting back up over the summer.

The numbers lingered around 40,000 to 50,000 from mid-August through early October before surging again to record levels, crossing 100,000 for the first time on Nov. 4 and reaching 200,000 for the first time on Nov. 27.