July 15, 2021 -- Two doses of Pfizer’s COVID-19 vaccine were 78% effective in preventing infection in pregnant women in Israel, according to a new study published Monday in JAMA.

In addition, none of the patients reported severe adverse reactions to the vaccines.

“Vaccination compared with no vaccination was associated with a significantly lower risk for SARS-CoV-2 infection,” the authors wrote.

“Although SARS-CoV-2 infection in pregnant women is mostly asymptomatic or mild, it may result in severe complications, including admission to the intensive care unit and mechanical ventilation, particularly in the third trimester,” they wrote. “Symptomatic SARS-CoV-2 infections in women also have been linked to a greater likelihood of preterm delivery and fetal intrapartum distress.”

Researchers at Maccabi Healthcare Services in Tel Aviv analyzed data for more than 15,000 women in a pregnancy registry, including 7,530 vaccinated women and 7,530 unvaccinated women matched by age, gestational age, residential area and the number of times they had given birth.

About 36% of the women were in the second trimester, and 33% were in the third trimester. The vaccinated women received their first dose between Dec. 19 and Feb. 28 and were followed through April 11.

Overall, COVID-19 cases occurred in 118 vaccinated women and 202 unvaccinated women, which equals 1.57% of the vaccinated group and 2.7% of the unvaccinated group. During the follow-up period, which ranged from 28 to 70 days, there were 10 infections in the vaccinated group and 46 in the unvaccinated group.

As more time passed, the risk of infection declined for the women who had been vaccinated. The researchers estimated that, at 28 days or more after vaccination, the efficacy was 78%.

In the vaccinated group, 68 patients reported adverse reactions, though none were severe. The most common symptoms were headache, weakness, pain and stomachache, which resolved within about a day.

During the follow-up period, about 18% of each group reached the end of their pregnancy. The researchers didn’t find any significant differences between the groups in terms of the rates of preeclampsia, infant birth weight, abortion, stillbirth or maternal death.

WebMD Health News Brief

Sources

JAMA: “Association Between BNT162b2 Vaccination and Incidence of SARS-CoV-2 Infection in Pregnant Women.”

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