Maternal immunity can help protect early-stage infants

Highlighting the importance of pregnancy immunization

Maternal antibodies are transferred via the placenta... the infant immunization gap can be complemented

Accumulating evidence supports immunization against influenza and pertussis...RSV vaccines are recommended worldwide

Attention is drawn to maternal immunization as a strategy that extends beyond preventing maternal infections to complement the immune gap in infants immediately after birth.

​Leading experts believe that transferring maternal antibodies generated during pregnancy to the fetus via the placenta can help protect early-stage infants, whose immune systems are not yet fully mature, from infectious diseases.

​On the 10th, Pfizer Korea hosted the '2026 Pfizer Press University' under the theme "Current State and Importance of Maternal Immunization: Understanding Maternal Immunity and Antenatal Protection."

​Professor Ja Young Kwon, Department of Obstetrics and Gynecology, Severance Hospital

At the event, Professor Ja Young Kwon of the Department of Obstetrics and Gynecology at Severance Hospital and Professor Hyun-Joo Seol of the Department of Obstetrics and Gynecology at Korea University Guro Hospital presented the principles of vaccination during pregnancy, real-world clinical application, and the medical significance of infant protection through maternal immunity.

​During pregnancy, various physiological changes occur across the immune, respiratory, and cardiovascular systems. Consequently, when infections occur, the risk of disease severity, hospitalization, or severe complications can increase. Furthermore, inflammatory responses driven by severe infections can adversely affect pregnancy outcomes, such as preterm birth or stillbirth.  

​Professor Kwon stated, "Maternal immunization not only protects the mother herself, but also holds vital significance in protecting the fetus and the newborn after birth."

​Although newborns are exposed to various pathogens immediately after birth, their immune systems remain insufficiently mature. Even following vaccination, establishing adequate immunological memory requires repeated doses and time.  

​According to Professor Kwon, newborns have a high proportion of naive immune cells that have not encountered antigens at birth, and their capacity to rapidly differentiate into memory B cells, which govern long-term immunity following antigen exposure, is limited compared to adults. Consequently, a vulnerable 'immune gap' susceptible to infection can occur during early infancy.

Utilizing maternal antibodies to bridge the postbirth vulnerability window

​Maternal immunity serves as a key strategy to bridge this immune gap in early life.  

Because it takes time for infants to develop sufficient immunity, a vulnerable window for infection inevitably arises in early life. Experts explain that elevating maternal antibody levels through vaccination during pregnancy directly increases the volume of antibodies transferred to the fetus.  

​When a pregnant woman generates antibodies via vaccination, immunoglobulin G (IgG) antibodies cross the placenta to the fetus. The infant can then utilize these maternally derived antibodies after birth to respond to infection.

​Gestational timing also impacts antibody transfer. The expression of Fc receptors responsible for IgG transport across the placenta increases progressively toward late pregnancy.  

​Professor Kwon noted that transplacental transfer of maternal IgG becomes highly active starting around 28 to 32 weeks of gestation, with fetal antibody concentrations rising toward late pregnancy. Accordingly, administration is timed during late pregnancy based on specific vaccine characteristics to align peak maternal antibody response with optimal transplacental transfer windows.  

​Professor Kwon explained, "If we elevate maternal antibody levels through vaccination before transfer, the infant can start life with high antibody titers from the moment of birth," and added, "Even as antibody levels gradually wane later on, the baby can remain protected over a longer duration."

​She added, "Maternal immunization delivers a triple benefit: protecting the mother, protecting the fetus, and ultimately protecting the newborn."

​Accumulating clinical evidence for maternal vaccines… Global expansion of target populations

Seol, Department of Obstetrics and Gynecology, Korea University Guro Hospital

Maternal immunization is already widely utilized in real-world clinical practice, primarily centered on influenza and pertussis.

​Professor Hyun-Joo Seol emphasized that influenza vaccination reduces infection risks and disease severity in mothers while concurrently helping prevent infections in infants during early life.

​In particular, influenza vaccination holds significant medical value in bridging the immune gap before 6 months of age, when infants are not yet eligible for direct vaccination. Citing domestic and international real-world data, Professor Seol added that maternal vaccination reduced maternal influenza infection and hospitalization risks, while protective efficacy against infection was also confirmed in infants.  

​Pertussis vaccination carries a distinct objective of infant protection. While pertussis often presents with mild severity in adults, it can cause severe complications such as apnea or lead to mortality in infants under 1 year of age, particularly those under 2 months.

​Consequently, administering the Tdap vaccine during pregnancy to transfer maternal antibodies to the fetus serves as an established strategy to protect infants until they receive their primary pediatric immunization.

​Recently, the application of maternal immunity has expanded to include respiratory syncytial virus (RSV).  

​While RSV infection often manifests as a mild cold in adults, it can precipitate severe lower respiratory tract infections, such as bronchiolitis and pneumonia, in infants and young children. It is regarded as a critical target for prophylaxis due to the heavy clinical burden of hospitalizations and ICU admissions in infants under 1 year old.  

​Professor Seol highlighted that unlike conventional maternal vaccines, the RSV vaccine was designed from its initial clinical development stage with the primary objective of protecting infants via maternal passive immunity.

​Professor Seol noted, "While influenza and COVID-19 vaccines were originally developed for the general population and subsequently accumulated clinical data in pregnant women, the maternal RSV vaccine differs in that it was specifically engineered from inception to protect infants through maternal passive immunity."

​Globally, more countries are integrating maternal RSV immunization into public health policy.

​According to Professor Seol, several countries have incorporated maternal RSV vaccines into their National Immunization Programs (NIPs). At the same time, guidance in the United States recommends late-pregnancy vaccination to prevent RSV-associated lower respiratory tract disease in infants after birth.

​Professor Seol stated, "Maternal vaccination represents a critical passive immunization strategy that protects the mother while bridging the immune gap in infants immediately after birth," and concluded, "From now on, when applying novel vaccines to pregnant women, providing robust evidence and accurate communication regarding gestational safety alongside clinical efficacy will be crucial."