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 Food and Drug Administration authorized shortening the waiting period Friday for the Moderna COVID-19 vaccine booster shot to five months.

Previously, fully vaccinated adults had to wait six months before receiving a booster.

Recently, the FDA made similar changes to the Pfizer-BioNTech booster after early data showed the omicron variant was able to -- at least partially -- evade the protection offered by two doses.

“The country is in the middle of a wave of the highly contagious omicron variant, which spreads more rapidly than the original...virus and other variants that have emerged,” Dr Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a statement.

The statement continued, “Vaccination is our best defense against COVID-19, including the circulating variants, and shortening the length of time between completion of a primary series and a booster dose may help reduce waning immunity."