Pfizer’s COVID vaccine shows 78% effectiveness during pregnancy

Two doses of the Pfizer / BioNTech COVID-19 vaccine were 78% safe and effective in preventing infection in pregnant women in a real-world study in Israel.

Led by researchers at Maccabi Healthcare Services in Tel Aviv, the retrospective observational study was published yesterday in JAMA. This involved analyzing data from 15,060 women in a pregnancy registry of a large state-mandated health system who were vaccinated with a first dose from December 19, 2020 to February 28, 2021.

Women were matched in a 1: 1 ratio with unvaccinated pregnant women by age, gestational age, residential area, population subgroup, number of deliveries, and influenza vaccination status (an indicator of research behavior for care) and followed until April 11, 2021.

Risk decreased in vaccinees over time

Among the 7,530 vaccinated women, 118 (1.6%) were infected with SARS-CoV-2 at least 28 days after their first dose of the BNT162b2 vaccine, compared with 202 among the 7,530 (2.7%) women not. vaccinated. The cumulative incidence was 1.85% in vaccinated and 3.90% in unvaccinated women, a difference of 2.05 percentage points. COVID-19-related hospitalization rates were 0.2% among vaccinated women and 0.3% among unvaccinated.

“In this large population-based cohort of pregnant women, BNT162b2 vaccination versus no vaccination was associated with a significantly lower risk of SARS-CoV-2 infection, although the absolute risk difference either low, “wrote the study authors.

Eighty-eight of 105 infected vaccinated women (83.8%) had symptoms of coronavirus, compared to 149 of 179 (83.2%) among unvaccinated women, a non-significant difference.

At 28 days, 4,788 of 7,530 (63.6%) women remained on follow-up in each group. The absolute cumulative number of events was 109 in vaccinated women and 158 in unvaccinated, and the cumulative difference in incidence was 0.80%. The cumulative incidence was 1.55% in the vaccinated group and 2.34% in the unvaccinated group.

Over 28 to 70 days of follow-up, 10 vaccinated and 46 unvaccinated women tested positive for coronavirus (hazard ratio [HR], 0.33% vs. 1.64%, respectively), for an absolute difference of 1.31% and an adjusted RH (aHR) of 0.22.

The risk reduction increased over time after vaccination, as indicated by a time varying covariate. During the 10 days following vaccination, there was no significant difference between HRa (0.96) in the two groups of women. But among those vaccinated, there was a statistically significant reduction in risk from 11 to 27 days after vaccination (aHR, 0.46).

During follow-up, 18.4% of the vaccinated group and 18.9% of the unvaccinated group reached the end of pregnancy. There were no significant differences between groups in terms of rates of preeclampsia (maternal hypertension and organ damage), babies smaller than expected for gestational age, birth weight, abortion, stillbirth , maternal death or pulmonary embolism (blockage of a pulmonary artery).

No serious adverse events

While 68 patients reported vaccine-related adverse events, none were serious. The most common side effects were headaches (10 [0.1%]), weakness (8 [0.1%]), pain unspecified (6 [less than 0.1%]) and upset stomach (5 [less than 0.1%]). All symptoms disappeared within 1 day.

Among the vaccinated women, 46% were in their second or third trimester, compared to 33% in the unvaccinated group. The mean age was 31.1 years and the median follow-up for SARS-CoV-2 infection was 37 days.

The authors noted that changes in hormone levels and immune function during pregnancy can increase the risk of viral infection. And although COVID-19 infection during pregnancy is usually asymptomatic or mild, it can lead to intensive care unit admission and mechanical ventilation, especially in the third trimester. Symptomatic infections have also been linked to higher risks of preterm delivery and fetal distress during childbirth.

The study was particularly important, the researchers said, because while the Pfizer vaccine was shown to be 85% effective in preventing infection 7 or more days after the second dose in a Phase 3 clinical trial, the women speakers were not included.