Two new studies published by the Centers for Disease Control and Prevention Friday add further evidence of the risks COVID-19 poses during pregnancy -- especially during the delta surge.

One study found the risk of stillbirth was nearly doubled among pregnant women with COVID-19 compared with pregnant women without COVID-19. The risk of stillbirth increased as the highly transmissible delta variant took hold across the nation. The risk of stillbirth is now four times greater -- up from one-and-a-half times greater -- since the delta variant first appeared.

The other study found that pregnant women with COVID-19 were more likely to die compared with non-pregnant women of similar ages who were also infected. The study, which looked specifically at infections in Mississippi, also found that the delta surge made things worse. Pre-delta, roughly five out of 1,000 pregnant women with COVID-19 died during pregnancy; during delta's predominance, the rate was 25 per 1,000.

The latest studies reinforce the urgent call for pregnant people to get vaccinated, though only 35% were fully vaccinated prior to or during their pregnancies, in the most recent count by the CDC. COVID-19 vaccines are safe and recommended for pregnant people.

-ABC News' Lauren Joseph and Sony Salzman

Centers for Disease Control and Prevention Director Rochelle Walensky has endorsed the CDC advisory committee's recommendation for Modern and Pfizer vaccine boosters for all recipients ages 18 and older who were vaccinated at least six months ago.

"After critical scientific evaluation, today’s unanimous decision carefully considered the current state of the pandemic, the latest vaccine effectiveness data over time, and review of safety data from people who have already received a COVID-19 primary vaccine series and booster," Walensky said in a statement Friday evening, hours after the committee's recommendation. "Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays. Based on the compelling evidence, all adults over 18 should now have equitable access to a COVID-19 booster dose."

-ABC News' Cheyenne Haslett

The CDC's independent advisory committee on Fridayvoted unanimously to recommend that everyone 18 and older who was vaccinated with Pfizer or Moderna at least six months ago can get a booster.

The FDA authorized Pfizer and Moderna boosters for all adults earlier on Friday.

The last step in the regulatory process will be CDC director Rochelle Walensky issuing her recommendation.

-ABC News' Cheyenne Haslett

The U.S. is currently averaging more than 88,000 new cases per day -- a nearly 40% increase since late-October, according to federal data. This increase marks the first surge in daily national cases after nearly 10 weeks of declines.

Michigan, which is now reporting more cases than at any other point in the pandemic, has the nation's highest infection rate, followed by Minnesota, New Mexico, New Hampshire, North Dakota, Wisconsin and Vermont. Puerto Rico, Florida and Hawaii have the nation's lowest infection rate, according to federal data.

One in every 427 Americans has died from COVID-19, according to data from Johns Hopkins University.

Over the last month, the U.S. has reported nearly 37,000 COVID-19 deaths, according to federal data.

Wyoming currently has the country's highest death rate, followed by Montana, West Virginia, Kentucky and Idaho, according to federal data.

-ABC News' Arielle Mitropoulos