Infectious Disease

Hybrid immunity in pregnancy increases COVID-19 protection for infants

Evan Vega January 12, 2024

0 93 2 minutes read

January 12, 2024

2 min read

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Key takeaways:

Infants in the United States are not eligible to receive a COVID-19 vaccine until age 6 months.
Hybrid immunity in pregnancy increases COVID-19 protection for infants that lasts up to 6 months.

Hybrid SARS-CoV-2 immunity in pregnancy — immunity from a prior infection plus vaccination — is associated with a greater likelihood of protection at delivery for mothers and infants compared with a prior infection alone, a study found.

“While [hybrid immunity] appears to provide more durable SARS-CoV-2 antibody responses in general, the role of hybrid immunity on durability of maternally derived functional — ie, neutralizing — antibody responses in pregnant people and their infants has not been well characterized,” Sylvia M. LaCourse, MD, MPH, associate professor of global health and medicine at the University of Washington, told Healio.

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Previous SARS-CoV-2 infection alone during pregnancy did not guarantee maternally derived antibodies or long-term protection to infants, but hybrid immunity incorporating vaccination did. Image: Adobe Stock.

LaCourse noted that infants aged younger than 6 months — who are not eligible to receive a COVID-19 vaccine — “rely on maternally derived antibodies for protection before they are eligible for their own vaccine.”

“While COVID-19 vaccination in pregnancy is recommended, including among pregnant people with history of natural infection, we wanted to know whether hybrid immunity was associated with stronger and more durable responses compared to infection alone,” she said.

LaCourse and colleagues conducted a prospective cohort study of pregnant people with a prior SARS-CoV-2 infection, collecting their blood and testing it for anti-spike IgG and neutralizing antibodies during pregnancy, at delivery and postpartum.

Of 107 participants, 40% were unvaccinated, 60% were vaccinated with at least one dose at the time of enrollment, 102 had a previous SARS-CoV-2 infection during pregnancy and five were diagnosed just before pregnancy.

According to LaCourse and colleagues, among people with a SARS-CoV-2 infection during or immediately before pregnancy and their infants, hybrid immunity was associated with a greater likelihood of having detectable anti-spike IgG+ and neutralizing antibodies at delivery for both them and their infants.

Specifically, data showed that at delivery, fewer unvaccinated participants (87% anti-spike IgG+, 86% neutralizing antibodies) and their infants (86%, 75%) had anti-spoke IgG+ or neutralizing antibodies compared with vaccinated participants and their infants (100% for all).

Additionally, the researchers found that 100% of infants born to participants with SARS-CoV-2 hybrid immunity before delivery retained anti-spike IgG and neutralizing antibodies until age 6 months, whereas 50% of infants born to pregnant people with a prior infection alone maintained anti-spike IgG+ status and only 14% retained functional neutralizing antibodies during this period.

“We found natural infection in pregnancy without vaccination did not ensure efficient transplacental transfer of maternally derived antibodies or long-term protection to infants through 6 months of age,” LaCourse said. “These data further support vaccination in pregnancy prior to delivery, including after infection, to ensure protection for both pregnant people and their infants.”

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