The White House and USPS have finalized a plan to mail out 500 million free at-home rapid COVID-19 tests to Americans, a source briefed on the plan told ABC News.

It comes as the first contract to produce the tests was awarded to a testing company Thursday night, a White House spokesperson confirmed.

The main issue that was delaying the finalization of the plan was whether or not USPS can retain 40,000 temporary holiday season workers to help deliver the tests.

However, it's not clear how many tests will be available from the first contract or how exactly USPS will deliver them. The White House has been vague on the timeline and has yet to launch a website through which Americans can order the tests.

The USPS-White House deal was first reported by The Washington Post.

-ABC News' Lucien Bruggeman, Cheyenne Haslett and Sasha Pezenik

COVID-19 vaccines can cause temporary changes to menstrual cycles, a new study from Oregon Health and Science University suggests.

Researchers looked at nearly 4,000 women who use Natural Cycles, a Food and Drug Administration-approved birth control app.

They found that some women who received COVID-19 vaccines experienced changes, with the most common being periods starting late by about one day.

However, the effects were temporary with a normal menstrual cycle returning within one or two months after getting the shot.

The team emphasized the findings do not mean COVID-19 vaccines have an impact on current or future fertility.

-ABC News' Katie Kindelan

The COVID-19 hospitalization rate for U.S. children between ages 0 and 4 has hit a record high, according to new data from the Centers for Disease Control and Prevention published Friday.

For the week ending Jan. 1, 2021, the hospitalization for young kids was 4.3 per 100,000.

"While children still have the lowest rate of hospitalization, pediatric hospitalizations are at their highest point compared to any other point prior in the pandemic," CDC director Dr. Rochelle Walensky said during a media call with reporters Friday.

Children under age 5 are currently not eligible to be vaccinated.

NBA star Rudy Gobert tested positive for COVID-19 Thursday, his second time infected.

According to his team, the Utah Jazz, Gobert took two rapid tests on Wednesday, both of which came back negative, but a PCR test that was analyzed overnight came back positive.

He revealed at press conference in September 2020 that he is fully vaccinated.

In a press conference from March 2020, which went viral, Gobert joked about growing concerns regarding COVID-19 by touching every single microphone as he made his way out of the room.

Days later, he developed flu-like symptoms while in Oklahoma for a game against the Oklahoma City Thunder and tested positive.

The Jazz and the NBA learned of his positive test moments before the game was set to start. The game was canceled and, hours later, the NBA suspended the 2019-20 season.

Gobert has been ruled out for Friday's game against the Toronto Raptors. It's unclear how long he will be out, but players who are placed on the virus-related protocols list are typically out for at least a week.

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