Vaccines protect pregnant patients from needing medical care during delta, omicron waves

Pregnant people who received messenger RNA COVID-19 vaccines were protected against COVID-19-related ED and urgent care visits and hospitalization when the delta and omicron variants were predominant, according to a case-control study.

“Vaccine effectiveness (VE) estimates among pregnant people are accruing, yet, to our knowledge, few studies have focused on more severe COVID-19 outcomes or provided variant-specific estimates,” Stephanie J. Schrag, DPhil, a general health scientist on the CDC COVID-19 Emergency Response Team in Atlanta, and colleagues wrote in JAMA Network Open. “We analyzed data from pregnant people in the VISION Network to estimate messenger RNA VE of two doses and of a single booster dose against laboratory-confirmed COVID-19-associated ED and urgent care (ED/UC) visits and hospitalizations during periods of delta and omicron variant predominance.”

Across a U.S. network of 306 hospitals and 164 ED/UC facilities, Schrag and colleagues identified pregnant patients who were hospitalized or went to ED/UC facilities for COVID-19-like illness between June 1, 2021, and June 2, 2022. Eligible patients also underwent molecular testing for SARS-CoV-2 infection during the 14 days before their hospitalization or ED/UC visit — collectively termed “medically attended events” — or in the 72 hours after.

The researchers divided the study period based on which COVID-19 variant comprised at least 50% of new cases in state and local surveillance data. Depending on location, the delta period ranged from June 1 to Dec. 15, 2021, and the omicron period ranged from Dec. 16, 2021, to Feb. 26, 2022.

Schrag and colleagues estimated VE “by comparing the odds of prior vaccination among patients with COVID-19-like illness and positive SARS-CoV-2 results (ie, cases) and those with negative results (ie, controls) using logistic regression,” the researchers wrote. They compared VE among pregnant patients who had received two doses or three doses of a messenger RNA (mRNA) vaccine and who were unvaccinated. They also noted how long it had been since patients received the vaccine.

In total, 4,517 ED/UC patients and 975 hospitalized patients were eligible for inclusion. Among these, 885 (19.6%) and 334 (34.3%) tested positive for SARS-CoV-2, respectively.

Delta-predominant period

During the delta period, the VE of pregnant patients who had received two doses of the vaccine within 14 to 149 days was 84% (95% CI, 69-92) against ED/UC visits and 99% (95% CI, 96-100) against hospitalization. For patients who received two doses 150 days or more prior to a medically attended event, the VE against ED/UC visits was 75% (95% CI, 5-93) and the effectiveness against hospitalization was 96% (95% CI, 86-99).

Patients who received a third dose of the COVID-19 vaccine within 7 to 119 days before their medically attended event had a VE of 81% (95% CI, 30-95) against ED/UC encounters and a VE of 97% (95% CI, 79-100) against hospitalization. There was not a “sufficient” sample to determine VE for patients who received three doses 120 days or more prior to their medically attend event, Schrag and colleagues wrote.

Omicron-predominant period

VE against ED/UC visits and hospitalization during the omicron-predominant period was 3% (95% CI, 49 to 37) and 86% (95% CI, 41-97), respectively, for patients who received two doses within 14 to 149 days. For those who had received two doses at least 150 days prior to a medically attended event, the VE was 42% (95% CI, 16 to 72) against ED/UC visits and 64% (95% CI, 102 to 93) against hospitalization.

Among patients who received three doses within 7 to 119 days and 120 days or more prior to their medically attended event, the VE against ED/UC visits was 79% (95% CI, 59-89) and 124% (95% CI, 414 to 2), respectively. Against hospitalization, the VE was 86% (95% CI, 28%-97%) and 53% (95% CI, 1,254% to 83%), respectively.

Of note, 65.4% of hospitalizations for COVID-19-like illness were associated with delivery. Patients who delivered during hospitalization had similar lengths of stay compared with both their nondelivering and nonpregnant counterparts. However, greater proportions of delivering patients who were hospitalized underwent mechanical ventilation and ICU admission compared with nondelivering and nonpregnant patients, “suggesting that the outcome used for this study did not reflect incidental infection among women admitted for delivery,” the researchers wrote.

“The findings reported here that COVID-19 maternal vaccination appears to protect pregnant people against medically attended COVID-19 is important given accruing evidence of increased risks of severe maternal morbidity and mortality associated with COVID-19 during pregnancy,” Schrag and colleagues wrote.