Maternal vaccination reduces COVID-19 hospitalization risk in offspring

Full vaccination (two doses) with an mRNA COVID-19 vaccine during pregnancy was associated with a reduced risk of COVID-19-related hospitalization among infants younger than 6 months of age, according to a recent study.

“Maternal vaccination [defined as the completion of two doses of BNT162b2 or mRNA-1273 COVID-19 vaccines] may have dual benefits; vaccination provides pregnant persons with protection and may also provide the added benefit of protecting their infants, who would not be eligible for vaccination,” said the researchers.

In this case-control study with a test-negative design, the researchers gathered data from the CDC-funded Overcoming COVID-19 Network and analysed 537 case infants hospitalized due to COVID-19 and 512 control infants hospitalized due to non-COVID-19 illness. Of these, only 87 case infants and 147 control infants were born to mothers who were fully vaccinated with an mRNA vaccine (BNT162b2 or mRNA-1273 vaccine) during pregnancy. [N Engl J Med 2022;387:109-119]

Overall, maternal vaccine effectiveness against COVID-19-related hospitalization among infants was 52 percent, with 70-percent vaccine effectiveness against intensive care unit (ICU) admission.

In particular, case infants who were born to mothers fully vaccinated during pregnancy had a lower incidence of admission to ICU (13.0 percent vs 23.0 percent) and critical COVID-19 (9.0 percent vs 12.0 percent) than those born to mothers who had not been fully vaccinated.

These results led to a reduction in the need of invasive (3.0 percent vs 7.0 percent) and noninvasive mechanical ventilation (6.0 percent vs 8.0 percent) and vasoactive infusions (1.0 percent vs 3.0 percent) among case infants born to fully vaccinated mothers vs infants whose mothers had not been fully vaccinated.

Two infants died due to COVID-19 and two infants received extracorporeal membrane oxygenation; these four case infants were born to unvaccinated mothers.

With regard to the variant predominance period, a greater reduction in the risk of COVID-19- associated hospitalization among infants was observed during the delta-predominant period than during the omicron-predominant period (80.0-percent vs 38.0-percent risk reductions). “[This finding was] consistent with the lesser degree of protection observed against omicron- … [vs] delta-associated hospitalization among vaccinated children and adults,” the researchers noted. [MMWR Morb Mortal Wkly Rep 2022;71:352-358; BMJ 2022;376:e069761]

Additionally, higher vaccine effectiveness against COVID-19-related hospitalization was observed for either variant when the second dose of vaccine was given after 20 weeks of pregnancy than during the first 20 weeks of pregnancy (69.0 percent vs 38.0 percent).

“[Previous] studies have shown that the mRNA vaccines (BNT162b2 and mRNA-1273) have been highly effective in preventing severe COVID-19 during pregnancy,” the researchers said. [J Clin Invest 2021;131:e153662; Nat Med 2021;27:1693-1695]

“In this real-world evaluation, maternal vaccination with mRNA vaccines was associated with a substantial reduction in the risk of COVID-19-related hospitalization and critical illness among young infants [during the first 6 months of age], although reductions were less pronounced when the omicron variant was predominant,” they said.

“[The results of this current study] provide compelling evidence that maternal vaccination is effective … This evidence that COVID-19 vaccines help to protect infants as well as mothers is highly relevant for patient counselling: a “two-for-one” deal may encourage more mothers to receive COVID-19 vaccination,” wrote Dr Sonja Rasmussen and Dr Denise Jamieson from the University of Florida College of Medicine in Gainesville, Florida, US, and Emory University School of Medicine in Atlanta, Georgia, US, respectively, in an editorial. [N Engl J Med 2022;387:178-179]