A testing company confirmed Wednesday the first known case in Southern California of "flurona," in which someone is infected with COVID-19 and the flu at the same time.

911 COVID Testing told KABC the case was detected at the Getty Center in Brentwood -- a suburban neighborhood in the city of Los Angeles -- in a teenage boy.

The minor was returning from vacation with his family in Cabo San Lucas, Mexico.

Steve Farzam, the testing company's chief operating officer, said the patient has symptoms but was not hospitalized. Since his test, one of his parents has also tested positive for COVID-19, but not the flu.

The White House said Wednesday it is confident it can deliver millions of rapid COVID-19 tests to Americans in January.

Last month, the administration announced it was planning to distribute 500 million free at-home rapid tests across the country to combat the surging omicron variant.

However, a website has yet to be launched where people can order the tests and the U.S. is currently producing less than half of the tests needed -- 200 million a month.

During a virtual briefing, Jeff Zients, the White House Coronavirus Response Coordinator, said the government not only has the capacity to deliver 500 million tests, but it also won't dip into the current supply on pharmacy shelves.

"With all the companies that now have been authorized, there’s the capacity for the U.S. government to purchase the 500 million now and not disrupt, or in any way cannibalize, the tests that are on pharmacy shelves and on websites and used and other settings," he said.

-ABC News' Cheyenne Haslett

Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Wednesday the definition of being fully vaccinated against COVID-19 is not changing to include booster shots.

"Individuals are considered fully vaccinated against COVID-19 if they've received their primary series. That definition is not changing," she said during a virtual briefing of the White House COVID-19 Response Team.

This means Americans are considered fully vaccinated if they have gotten two shots of either the Pfizer-BioNTech or the Moderna vaccine or one shot of the Johnson & Johnson vaccine.

However, Walensky did urge those who have been fully vaccinated to stay "up to date" on additional doses they may be eligible for based on their age and which vaccine they received.

About 1 in 15 people in England tested positive for COVID-19 in the week ending Dec. 31, 2021, according to new data published Wednesday by the UK's Office of National Statistics -- a jump from 1 in 25 the week before.

This means that an estimated 3,270,800 people in the country caught the virus last week, with the most infections occurring among those between ages 17 and 24, the ONS said.

Additionally, 1 in 20 people contracted COVID last week in Scotland and Wales as did 1 in 25 people in Northern Ireland.

The ONS noted that these estimates do not include people who tested positive in "hospitals, care homes and/or other communal establishments."

The American Medical Association, the nation’s largest association of physicians, has criticized the Centers for Disease Control and Prevention's new quarantine and isolation guidance for COVID-19, saying the recommendations "are risking further spread of the virus."

The CDC updated its guidelines on Dec. 27, saying asymptomatic people who test positive for COVID-19 should self-isolate for five days rather than 10.

"The American people should be able to count on the Centers for Disease Control and Prevention (CDC) for timely, accurate, clear guidance to protect themselves, their loved ones, and their communities. Instead, the new recommendations on quarantine and isolation are not only confusing, but are risking further spread of the virus," the American Medical Association's president, Dr. Gerald E. Harmon, said in a statement Wednesday night.

Harmon referenced data cited by the CDC in its rationale for shortening the isolation period, which estimates 31% of people remain infectious five days after a positive COVID-19 test, suggesting that data proves thousands of Americans could return to their lives while still infected.

"With hundreds of thousands of new cases daily and more than a million positive reported cases on January 3, tens of thousands -- potentially hundreds of thousands of people -- could return to work and school infectious if they follow the CDC’s new guidance on ending isolation after five days without a negative test," Harmon said. "Physicians are concerned that these recommendations put our patients at risk and could further overwhelm our health care system."

Harmon said a negative COVID-19 test should be required for ending isolation after a positive test, as reentering society without knowing whether an individual is still positive ultimately risks further transmission of the virus.

Although test availability remains an issue nationwide, Harmon also called on the Biden administration to ramp up production and distribution of tests, adding that "a dearth of tests at the moment does not justify omitting a testing requirement to exit a now shortened isolation."

-ABC News' Arielle Mitropoulos