COVID-19 updates: Classes in Chicago canceled for 4th day

COVID-19 vaccines do not increase the risk of premature or low-weight birth among babies born to pregnant vaccinated women compared with those born to unvaccinated women, according to a new study from the Centers for Disease Control and Prevention published Tuesday.

Researchers from Yale looked at electronic health data from more than 40,000 pregnant women from the CDC's Vaccine Safety Datalink.

There were 7.0 premature births for every 100,000 babies born among unvaccinated women compared to 4.9 births per 100,000 for babies born to women who received a COVID vaccine while pregnant.

Additionally, rates of low-birth weight were 8.2 per 100,000 in both the unvaccinated and vaccinated groups.

The team said the findings add to a growing body of evidence that getting vaccinated against COVID is safe for pregnant people and for their babies.

Pregnant women are at increased risk for severe illness, hospitalization and death from COVID-19, but only 40% have been vaccinated, CDC data shows.

The omicron variant accounts for 95% of all new COVID-19 cases in the U.S., according to data from the Centers for Disease Control and Prevention released Tuesday.

In early December, the highly transmissible variant made up 0.6% of new infections.

Meanwhile, the delta variant -- responsible for the summer surge -- makes up 4.6% of new cases, the CDC said.

The data also showed the omicron variant is dominant in all regions of the country. In the New York-New Jersey region and in the Southeast, the variant is linked to 98% of new infections.

-ABC News' Arielle Mitropoulos

The United Kingdom recorded more than 200,000 cases of COVID-19, according to the UK Health Security Agency.

The 218,724 new infections is the highest figure ever reported in a single day and an increase of nearly 60% from the number of cases reported on the same day last week.

However, there has been a backlog of data due to the holiday weekend so the number includes four days of data from Northern Ireland and two days of data from Wales, the UKHSA said.

-ABC News' Mike Trew

Sen. Rob Portman, R-Ohio, tested positive for COVID-19 last night, according to a press release. 

Portman took an at-home COVID test which came back positive. The senator said he is asymptomatic and feels fine.

"I have been in contact with the Attending Physician and my personal doctor. I am following their medical advice and following CDC guidelines and isolating for the recommended five days," Portman said in the statement.

He will be working remotely this week, but will not be able to be in Washington, D.C., for votes.