Drugmakers and U.S. regulators plan to launch clinical trials in January testing the safety of Covid-19 vaccines on pregnant women and young children, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
Those two groups were excluded from the first Covid-19 vaccine clinical trials until researchers could determine that the vaccine was relatively safe in healthy adults before testing it in more vulnerable populations.
Fauci noted Thursday in a discussion sponsored by Columbia University on Thursday that pregnant women have not been included in any Covid vaccine clinical trials to date. It's not clear if the omission means that pregnant women won't be able to receive an authorized vaccine until more safety data is collected.
Studies on pregnant women will come in later trials, he said.
"That will not necessarily be looking at efficacy, but we'll be looking at safety and immunogenicity to bridge to the efficacy in the adult non-pregnant population," he said at Columbia University's Grand Rounds 2020 event. "The same holds true for the pediatric population. Those studies will probably start in mid- to late-January."
Physicians have found an increased risk of complications for pregnant women who contract Covid-19, said Aron Hall, Covid response chief at the CDC.
"The early indication is there might be a higher risk of pre-term delivery," he said Thursday at the FDA's Vaccines and Related Biological Products Advisory Committee.
While young children appear to be less likely to die from Covid-19 when they get it, they are at an increased risk in developing something called Multisystem inflammatory syndrome in children, or MIS-C, researchers have found. It's an inflammatory disease that can affect multiple organ systems throughout the body, including the heart, lungs and brain.
Fauci's comments came as the FDA's vaccine advisory committee weighs whether to recommend the emergency approval of Pfizer's Covid vaccine.
Data on Pfizer's vaccine has shown it's been remarkably effective in the trial participants at preventing disease and the FDA is expected to authorize its emergency use as early as Friday.
The U.K.'s Medicines and Healthcare products Regulatory Agency, which authorized Pfizer's vaccine for broad use in adults last week, cautioned against giving it to women who are pregnant or breastfeeding.
Dr. Doran Fink, deputy director of the FDA's division of vaccines and related products, said Thursday there's "very limited data on use in pregnancy."
"We recognize that among the groups first prioritized for vaccine use under an EUA, there will be many women of childbearing potential, including women who are pregnant either knowingly or unknowingly," he said at the meeting Thursday afternoon. "We really have no data to speak to risks specific to the pregnant women or the fetus, but also no data that would warrant a contraindication to use in pregnancy at this time."
He added that under a so-called emergency use authorization, pregnant women and women of childbearing years will be "free to make their own decision."
The FDA told manufacturers, including Pfizer, that they should conduct DART studies, or developmental and reproductive toxicity studies, before they could enroll pregnant women and "women of childbearing potential who are not actively avoiding pregnancy" in vaccine trials, Pfizer spokeswoman Jerica Pitts told CNBC. DART studies are conducted in animals to assess the potential risks associated with a vaccine to a developing fetus.
"Pfizer recognizes that developing a potential SARS-CoV-2 vaccine for broad use is critically important to help stop the pandemic, including for potential use in pregnant women," Pitts said in a statement. "Pfizer is in the process of conducting DART studies and plans to submit available data to the agency."
Pfizer acknowledged at the FDA's vaccine meeting Thursday that it's missing information on the vaccine's affect on pregnant women, according to a slide presentation. Representatives for the company told the advisory committee that it expects preliminary results from its DART studies by mid-December.
The company also noted that it's also missing information on the effects of the vaccine in kids and teens under 16. The FDA's advisory committee will vote on its non-binding recommendation later Thursday and the FDA is expected to soon.
— CNBC's Amanda Macias contributed to this report.