COVID-19 Vaccination During Pregnancy Reduces Risk of Infant Infection

Providing mRNA COVID-19 vaccination during pregnancy to mitigate risk of maternal complications from COVID-19 was found to also protect the infant from infection and related hospitalization, in a recently published case-control study involving over 8000 infants.

Jeffrey Kwong, Institute for Clinical Evaluative Sciences (ICES), Toronto, Canada and colleagues in the Canadian Immunization Research Network (CIN) and the Provincial Collaborative Network (PCN) sought to determine whether the practice of vaccinating during pregnancy to promote transfer of maternal antibodies to protect infants from such infections as pertussis, tetanus, and influenza could also be effective against COVID-19.

“We sought to extend this evidence by evaluating the effectiveness of maternal vaccination with the primary, 2 doses, or primary plus booster, 3 doses, mRNA COVID-19 vaccine series during pregnancy against Delta and Omicron SARS-CoV-2 infection and hospital admission of infants during their first six months of life,” Kwong and colleagues explain.

In an editorial accompanying the study in the British Medical Journal, Dana Danino, MD, Pediatric Infectious Disease Unit, Soroka University Medical Center, Beer-Sheva, Israel and Ilan Youngster, MD, MMSc, Pediatric Infectious Disease Unit, Shamir Medical Center, Beer-Yaakov, Israel, point out the value of maternal COVID-19 vaccination providing coverage to infants during the “unprotected”vulnerable period before they can receive direct vaccination at 6 months of age.

They welcome the study by Kwong and colleagues to “address this gap,” noting that while there has been evidence that most infants born to vaccinated mothers retain SARS-CoV-2 maternal antibodies at 6 months of age, “evidence for protection against neonatal COVID-19 infection has been deficient.”

The test negative design study utilized data from the International Credential Evaluation Services (ICES). consistent with the Ontario, Canada health information privacy laws, to identify infants younger than 6 months of age born between May 7, 2021 and March 31, 2022 who were tested for SARS-CoV-2 between May 7, 2021 and September 5, 2022. The cohort of 8809 infants meeting criteria included 99 with the delta variant and 4365 controls, and 1501 with the omicron variant and 4847 controls.

Kwong and colleagues reported that the effectiveness of a 2-dose maternal vaccination against the infant becoming infected and subsequently hospitalized with the delta variant was, respectively, 95% (95% Confidence Interval 86-98%) and 97% (73-100%). Against the omicron variant, the 2-dose maternal vaccination was 45% (37-53%) effective against infection in the infant and 53% (39-64) effective against hospitalization. A third, booster dose during pregnancy increased effectiveness against omicron infection in the infant and subsequent hospitalization to 73% (61-80%) and 80% (64-89%), respectively.

The effectiveness of two-dose vaccination against infant omicron infection was highest (53% [42-62%]) when the second dose was given in the 3rd trimester: compared to 47% [31-59%) in the first and 37% [24-47%] in the second trimester.The apparent protection from the two-dose vaccination decreased from 57% (44-66%) between birth and eight weeks, to 40% (21-54%) after 16 weeks of age.

Kwong and colleagues emphasize that receiving only the first vaccine dose during pregnancy provided less protection than completing the two- or three-dose series. They also caution that while dosing in the third trimester was associated with higher effectiveness, “the clinical implications of this finding on maternal vaccination need to be weighed against the risks of delaying vaccination to the pregnant woman and the fetus.”

Danino and Youngster concur, suggesting that the timing of vaccination in pregnancy is not yet clear, and that delaying a maternal booster until the third trimester, “should be balanced against the potential harm to the mother and fetus associated with maternal COVID-19 occurring before receipt of the vaccine.”