COVID-19 Vaccine Effectiveness for Pregnant Women, Newborns Plummets During Omicron: CDC Data

A health care worker prepares Pfizer COVID-19 vaccine doses in Portland, Ore., in a file photograph. (Nathan Howard/Getty Images)

COVID-19 vaccine effectiveness has plummeted for pregnant women and newborns since the Omicron coronavirus variant became the dominant strain in the United States, according to data presented by Centers for Disease Control and Prevention (CDC) officials on Oct. 19.

The effectiveness of two doses of a Pfizer or Moderna vaccine against emergency department and urgent care visits was 87 percent after two doses and remained high at 78 percent after 150 or more days while the Delta variant was predominant, according to data from the CDC-funded VISION network.

However, two doses of the vaccines started at just 39 percent effectiveness against Omicron and dropped to 11 percent after 150 or more days, according to the data, which were presented to the CDC's vaccine advisory panel.

A third dose increased protection to 81 percent. Effectiveness wasn't available after 120 or more days for a third dose, or a vaccine booster, for pregnant women. But nonpregnant women of childbearing age saw vaccine booster effectiveness drop from 69 percent to just 16 percent after 120 or more days, according to the VISION data.

A third dose was estimated to provide 94 percent effectiveness against hospitalization for pregnant women but, again, no estimates were available for several months later or for two doses. For nonpregnant women aged 18 to 45, effectiveness for two doses started at 64 percent but decreased to 50 percent after 150 or more days. A third booster dose upped the protection to 73 percent, with no estimate available for 120 or more days.

The estimates were much lower for Omicron than during the Delta era.

The estimates were drawn from encounters from June 2021 to June 2022 in sites across 10 states, including California, Utah, and Illinois.

In addition to effectiveness data, CDC researchers presented data that show no increase in miscarriages linked to COVID-19 vaccine primary series or booster doses.

CDC advisers said the data support agency recommendations that virtually all pregnant women get vaccinated.

"With full confidence as a provider, I can strongly recommend this vaccine to my patients, to my pregnant patients who are about to have children," said Dr. Grace Lee, the advisory panel's chair. "This is actually very strong data."

Protection for Infants

Protection for infants up to 5 months old also plummeted after Omicron displaced Delta, CDC data show.

A two-dose primary series administered to mothers conferred just 38 percent effectiveness to their infants against Omicron hospitalization, data from the CDC-funded Overcoming COVID-19 Network show.

If a mother received her second dose in the first 20 weeks of pregnancy, her child had just 25 percent protection against hospitalization.

"During Omicron predominance, vaccines given in the first 20 weeks did not show effectiveness for infants," Dr. Katherine Fleming-Dutra, a CDC researcher, told the agency's vaccine advisory panel.

If a mother received her second dose after the first 20 weeks of pregnancy, her child had 57 percent protection against hospitalization.

That was down from 68 percent and 88 percent, respectively, during the Delta era.

The effectiveness "was lower during Omicron predominance, when there was mismatch between the vaccine and the predominant circulating variant," according to Fleming-Dutra.

The vaccines available in the United States are based on the Wuhan virus variant, which hasn't been in circulation since 2020.

Updated vaccine boosters recently became available, with no clinical data.

Not enough time has passed for the updated vaccine boosters to be analyzed through the CDC systems, researchers said.