Another 133,000 children tested positive for COVID-19 last week, according to a new report from the American Academy of Pediatrics and the Children’s Hospital Association. Hospital admissions among children have also increased by 20% over the last week, according to federal data.

The Northeast is currently seeing its highest number of child cases since the beginning of pandemic, though the Midwest continues to see the highest number of pediatric cases.

Twenty million children ages 5 to 17 have received at least one vaccine dose, accounting for about 38.3% of that population.

Severe illness due to COVID-19 remains "uncommon" among children, the two organizations wrote in the report. However, AAP and CHA continue to warn that there is an urgent need to collect more data on the long-term consequences of the pandemic on children, "including ways the virus may harm the long-term physical health of infected children, as well as its emotional and mental health effects."

-ABC News' Arielle Mitropoulos

Mississippi said it's confirmed its first case of the omicron variant, detected in a fully vaccinated person who recently traveled to New York, the state's Department of Health said.

The person's symptoms were not released but the health department said the individual was not hospitalized.

Mississippi is seeing "a minimal increase in the number of COVID patients in the hospital and a minimal increase of COVID patients in the ICU and on vents," the Department of Health added.

-ABC News' Michelle Stoddart

For the first time in two months, the U.S. is now averaging more than 100,000 new cases per day, according to federal data. On average, about 106,000 new cases are being reported each day -- up by about 27% in the last week, and by 65.4% since late-October.

New Hampshire currently holds the country's highest case rate, followed by Michigan, Minnesota, Vermont and Wisconsin. Puerto Rico, Hawaii and Florida have the lowest infection rate, according to federal data.

-ABC News' Arielle Mitropoulos

The omicron variant appears to be "dominating" new infections in most of South Africa's provinces, South African President Cyril Ramaphosa said in a newsletter Monday.

Ramaphosa said the number of daily cases has increased five-fold in the last week.

"As the country heads into a fourth wave of COVID-19 infections, we are experiencing a rate of infections that we have not seen since the pandemic started," he warned.

Just 24.41% of South Africa's population is fully vaccinated, according to Africa CDC. Ramaphosa said scientists in South Africa and around the world are working to answer critical questions about the new variant, and the urgent priority is to continue getting people vaccinated.

-ABC News' Christine Theodorou

Four cases of the omicron variant have been detected in Washington, D.C., health health officials announced Sunday.

The first case is a woman who recently traveled to Florida and New York.

The second case is a woman who traveled to Maryland during Thanksgiving, health officials said.

The third case is a man with no known travel, according to health officials.

The fourth case is a woman who traveled to Virginia during the Thanksgiving, health officials said.

All four patients are fully vaccinated; however, it is unclear if they have received booster shots, health officials said.

-ABC News' Beatrice Peterson