In the first few months of their lives, infants experience new sights, sounds, scents, and textures. During this time, they also make contact with new organisms. It takes up to three months for portions of infants’ still-developing immune systems to mature.1 During these early weeks and months, infants are too young to receive their first vaccines, leaving them vulnerable to developing serious infections.2

Most pregnant people transmit antibodies to their developing fetuses naturally starting in the second trimester and peaking in the third trimester. Babies born at full term often have even greater immunity than those who gave birth to them.3

Maternal vaccination is a longstanding practice; however, research into vaccines designed specifically for pregnant people is still somewhat new. Fortunately, scientists at the forefront of fetal health innovation are studying ways that vaccines given during pregnancy can continue to protect children in the months after birth.3

“Having a new baby can be a very exciting time in a person’s life,” says Annaliesa Anderson , Senior Vice President and Head of Vaccine Research and Development for Pfizer. “We want to help protect new babies from potentially serious, life-threatening infectious diseases. And we want to help protect families from the impact that having a baby with an infectious disease can have on their lives. Maternal immunization can help do both of those things.”

The unfortunate truth is that approximately 13,800 children die every day from infectious diseases.4 Vaccines in general are effective health interventions that can lead to the eradication of infectious diseases.So, it naturally follows that prioritizing maternal immunization could have a major impact on the health and wellbeing of newborns and their families.3

Protecting Against GBS and RSV through Maternal Immunization

Influenza has been linked to preterm labor, preterm birth, and fetal death. Pertussis infection, better known as whooping cough, can be fatal in infants.5 However, infants are too young to get these vaccines when they are newborns: the Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis) vaccine isn’t given to infants until they’re two months old, and the “flu” (influenza) vaccine is given at six months.6  This leaves newborns vulnerable against potentially serious illness—unless their mothers are vaccinated.

Both the influenza and Tdap vaccines are recommended to be given to mothers as a routine part of prenatal care. When pregnant people are vaccinated, vaccine antibodies are transferred to the fetus, providing critical protection against serious illnesses for pregnant parents and their newborns.3

Maternal vaccines have been used around the world to help protect infants against neonatal tetanus. A successful global vaccination campaign helped decrease the number of neonatal tetanus deaths from 170,829 in 2000 to 25,000 in 2018.7

“While vaccines against tetanus, influenza, and pertussis have been used in pregnant people for many years, no vaccine has been designed and approved specifically for use during pregnancy to help protect a newborn,” Anderson says. “Pfizer’s goal is to change that.”

Pfizer's Vaccine Research and Development team has been focused since 2015 on creating maternal vaccines. Specifically, the goal is to help ensure that mothers have enough antibodies to protect their babies against two of the most common infectious diseases among infants—respiratory syncytial virus (RSV) and Group B streptococcus (GBS).

Respiratory Syncytial Virus (RSV)

RSV is a common respiratory infection that resembles a mild cold in most adults and older children, but it can be dangerous for some young children, particularly premature infants, infants age 6 months or younger, and children with weakened immune systems or chronic diseases. In fact, 2% of children younger than six months of age with RSV infection may require hospitalization and may experience bronchiolitis (inflammation of the lungs) or pneumonia (infection in the lungs).8

Globally, approximately 6.6 million infants under 6 months of age are affected by RSV each year and about 45,000 die from the virus.9

Group B Streptococcus (GBS)

GBS is often found in people's gastrointestinal and genital tracts, including the vagina. These bacteria are typically harmless unless they invade the bloodstream or major organ systems, where they can cause infection, or GBS disease.10

The Centers for Disease Control and Prevention (CDC) also notes that GBS disease is most common in newborns11, who may be exposed to the bacteria as they pass through the mother's vagina during birth10 and can result in life-threatening infections such as bacteremia (bloodstream infections), sepsis (extreme inflammation throughout the body in response to an infection), pneumonia, and meningitis.11

“With Group B strep, we see far less disease than with RSV—about 400,000 cases globally every year—but it’s attributed to about 120,000 deaths,” Anderson says. “The babies who survive are [often] subjected to delayed cognitive development and, potentially, long-term developmental delays. By preventing the disease in the first place, we can have a large impact on those babies and their families.”

Leading the Way for Vaccine Innovation

Designing vaccines for moms is a fairly young science, but it has quickly become a global priority.12 Medical researchers and healthcare providers alike have seen the potential for maternal vaccines to prevent infant deaths, safely and effectively.

“It's important to vaccinate the mother in the second trimester and early in the third trimester of pregnancy to enable her to build an antibody response,” says Anderson. “It normally takes one to two weeks to get peak levels of antibodies, so they can be passed from the placenta through to the baby prior to birth, which is the most critical time for these antibodies to transfer.”

Given the importance of maternal vaccines, the U.S. Food and Drug Administration (FDA) fast-tracked clinical trials for the RSV and GBS maternal vaccine candidates in Pfizer's vaccine pipeline. The RSV vaccine entered Phase 3 clinical trials in June 2020, and in November 2022, Pfizer announced positive results from the study. The pre-planned, interim efficacy analysis met the success criterion for one of two primary endpoints. Data showed that the vaccine was 81.8% effective against severe illness in babies from birth through three months of age who received medical support, with 69.4% effectiveness during the six-month follow-up period.

Although the statistical success criterion was not met for the second primary endpoint, clinically meaningful efficacy of 57.1% was observed for medically attended lower respiratory tract illness (MA-LRTI) in infants from birth through three months of age. Efficacy for MA-LRTI of 51.3% was observed over the six-month follow-up period. In February 2023, Pfizer announced that the FDA accepted for review a Biologics License Application for its RSV vaccine candidate.13

Additionally, funding from the Bill & Melinda Gates Foundation is helping to advance the development and accessibility of the RSV and GBS vaccine candidates, which, if successfully developed and approved, may help improve infant health and promote global health equity.14 In May 2022, Pfizer also launched An Accord for a Healthier World, a  groundbreaking initiative to provide patented medicines and vaccines to more than 1 billion people in 45 lower-income countries.

“It's really exciting that we may soon have some specific vaccines that are licensed for pregnant people,” says Anderson. “It will help to protect them and also their babies before they're born and within those first few months of life.”