THURSDAY, Aug. 12, 2021 (HealthDay News) -- Since COVID-19 and three vaccines to help prevent it arrived in the United States, questions have swirled about their impact on pregnant women, new moms and infants.

How would the virus affect them and their health risks? Should women get the vaccine while pregnant or breastfeeding?

The U.S. Centers for Disease Control and Prevention offered an emphatic answer to those questions on Aug. 11, recommending all women who are pregnant or considering pregnancy get vaccinated. The vaccines are safe and effective, CDC leaders said.

The announcement came the same day JAMA Network Open published a pair of groundbreaking studies addressing the issues.

One focused on the potentially devastating impact of the SARS-CoV-2 virus on pregnant women, and the other on whether a new mom's COVID shot might confer benefits on her breastfed baby.

"Vaccination is the best method to reduce maternal and fetal complications of SARS-CoV-2 infection," said Dr. Jennifer Jolley, co-author of the new study on outcomes for expectant moms. "There are no specific exclusions to the recommendation for vaccination, and pregnant patients that have additional [diseases or medical conditions] are at elevated risk of adverse maternal outcomes from COVID-19 disease."

In the study, her team reported that the virus increases the risk of serious infection and death for pregnant women. It can also lead to a preterm birth with serious, long-term health effects for babies.

"Anything we can do to lower the chance that a mom and therefore a baby could be critically ill, I think, is absolutely warranted," said Jolley, an associate clinical professor of obstetrics and gynecology at the University of California, Irvine.

She and her colleagues reviewed data from close to 870,000 women who gave birth at nearly 500 U.S. medical centers between March 2020 and February 2021.

About 2% of the women -- 18,715 in all -- had COVID-19. Most were 18 to 30 years of age; they were more likely than those without the virus to be Black or Hispanic patients, the study said.

Besides being more likely than others to have a preterm birth, the women with COVID had significantly higher rates of admission to the intensive care unit, respiratory intubation and mechanical ventilation.

"The CDC has determined that pregnant individuals are at an increased risk for severe illness from COVID-19 when compared to non-pregnant people," said study co-leader Dr. Ninh Nguyen, head of surgery at UC Irvine. "This study expands our knowledge about risk for adverse outcomes."

Specifically, it reported that women with COVID had 15 times the risk of dying while in the hospital to give birth, compared to women without the virus.

And, researchers noted, respiratory failure requiring intubation in a pregnant patient can also impact the fetus, which depends on oxygen supplied by the mother through the placenta.

The CDC said an analysis of data from the v-safe COVID-19 Vaccine Pregnancy Registry found no increased risk of miscarriage among nearly 2,500 women who received an mRNA COVID vaccine before 20 weeks of pregnancy. It added that three safety monitoring systems found no safety concerns for women vaccinated late in pregnancy or for their babies.

"If you haven't gotten the vaccine yet and you are pregnant, get it right away, as soon as possible," said Dr. Lori Feldman-Winter, a New Jersey pediatrician who heads the American Academy of Pediatrics Section on Breastfeeding. She wasn't part of the study but reviewed the new research.

"This study just highlights the importance of prevention," she said, noting that COVID is preventable through vaccination and the vaccines are safe. Meanwhile, babies delivered preterm are susceptible to development issues and lifelong respiratory illnesses, Feldman-Winter added.

In a second study published Aug. 11 in JAMA Network Open, researchers in Spain reported that breast milk of 33 women who had the Pfizer-BioNTech mRNA vaccine contained antibodies for COVID-19 that increased after the second dose.

None of the women in the study had been infected with COVID before getting the vaccine. The main limitation of the study was its small size. The researchers, led by Dr. Vicens Diaz-Brito of the Department of Infectious Diseases at Parc Sanitari Sant Joan de Déu in Barcelona, also did not determine if antibody levels in breast milk decrease or plateau later after vaccination.

But Feldman-Winter noted that human milk has immune components that can teach an infant's immune system to respond to antigens, substances in blood that trigger the body to fight back. Other studies have shown that kids who are breastfed can get more robust responses to vaccines, Feldman-Winter said. This study reported the moms are making good immune responses to the vaccine, she said.

"If she's breastfeeding, that immune response is carried over and lasts at least a month," Feldman-Winter said.

While doctors don't know how much longer it lasts, she said the benefit probably continues as long as the mother produces milk, providing continued protection as the baby breastfeeds.

If so, that's a plus, Feldman-Winter said, "because we don't have a vaccine yet for babies and babies can get COVID."

More information

The U.S. Centers for Disease Control and Prevention has information on COVID-19.

SOURCES: Jennifer Jolley, MD, associate clinical professor, obstetrics and gynecology, Division of Maternal-Fetal Medicine, University of California, Irvine; Ninh Nguyen, MD, chair, Department of Surgery, University of California, Irvine; Lori Feldman-Winter, MD, MPH, chair, American Academy of Pediatrics, Section on Breastfeeding, and pediatrician, Cooper University Hospital, Camden, N.J.; JAMA Network Open, Aug. 11, 2021