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.

Mayo Clinic said it will lay off about 1% of its staff for failing to get at least one dose of the COVID-19 vaccine by a company deadline.

"While Mayo Clinic is saddened to lose valuable employees, we need to take all steps necessary to keep our patients, workforce, visitors and communities safe. If individuals released from employment choose to get vaccinated at a later date, the opportunity exists for them to apply and return to Mayo Clinic for future job openings," Mayo Clinic said in a statement to ABC.

Last October, Mayo Clinic had set a Jan. 3 deadline for all employees to get at least their first vaccine dose or face dismissal.

The health care organization said the number of staffers being let go was "comparable to what other health care organizations have experienced in implementing similar vaccine requirement programs."

Mayo Clinic employs about 73,000 people, according to its website.