What are the benefits of getting vaccinated while pregnant?

Alexa Nikolai
Sep 10, 2025
4 min read

A doctor injects a needle into a patient's upper arm to provide a vaccination

Overview

When babies are born, their immune systems are not yet fully matured, so they are unable to protect themselves from germs and infections as effectively. Fortunately, while they are growing in the womb, babies receive some temporary protection from their mothers that lasts until they are old enough to develop a mature immune system and receive vaccinations. Beyond the baseline level of protection, the process of maternal immunization, in which pregnant women are vaccinated during their second or third trimester, allows mothers to pass more specific protection onto their babies.

The Immune System

The immune system is a collection of organs, white blood cells, proteins, and chemicals in your body that protect you from illness and help you heal after an illness or an injury. Your immune system helps keep harmful organisms out of your body, destroys any that do get inside, limits harm from these attacks, and heals any damage that may have occurred.

Two key components of the immune system are white blood cells and antibodies. White blood cells are a certain type of cell that attack and eliminate harmful germs or other invaders in your body. Antibodies are proteins that help identify these invaders so that white blood cells know where to attack. Invaders, known as pathogens, that may trigger the immune system include bacteria, viruses, fungi, parasites, and cancer. When speaking of the immune system, the word antigen is used to describe a recognizable portion of any of these pathogens.

In order to destroy pathogens, your immune system first must recognize them. There are two layers of the immune system that accomplish this task in different ways:

Innate immunity: the natural protection that you have from birth
Acquired / adaptive immunity: protection that your body gains from experience and exposure

Innate immunity provides a generalized defense that does not target specific antigens. Adaptive immunity is developed over the course of your lifetime and allows your body to recognize specific antigens in order to launch a more effective attack.

Adaptive Immunity

Adaptive immunity is developed when your body is exposed to antigens. The first time your body sees a particular antigen, it only has use of the innate immune system to fight it off, which is not as effective. However, after exposure to that antigen, the body produces antibodies which are able to recognize that specific antigen. From then on, whenever your body is exposed to that antigen, the antibodies will recognize the threat early and allow the adaptive immune system to enact a more targeted and effective attack.

Against some pathogens, adaptive immunity may last forever. Against others, especially against pathogens that frequently mutate or change, such as the influenza virus, your adaptive immunity may become less effective over time.

Vaccination

Receiving vaccinations is one way to trigger your adaptive immune system. Vaccinations imitate infections by exposing your body to a small amount or non-dangerous version of a particular antigen, such as weakened or killed bacteria or viruses, bits of the exterior surface or genetic material of a pathogen, or a bacterial toxin treated to be non-toxic. This exposure engages the adaptive immune system while also preventing you from becoming too sick. Since the antibodies against that specific antigen are created after vaccination, if you are exposed to the actual pathogen later in life, your body will be able to recognize it and fight it off more effectively, saving you from severe illness.

Immune Systems in Babies

As mentioned above, when babies are born, their immune systems are not yet fully mature, so if they are exposed to disease-causing pathogens, their bodies won’t be able to develop antibodies and fight off the infection as effectively.

In the discussion so far, we’ve been discussing active immunity, which is adaptive immunity that is developed in your own body after exposure to an antigen (through illness or vaccination). However, another type of immunity is passive immunity, which is protection that your body gets by using antibodies produced by another human or animal. Passive immunity is shorter-lasting than active immunity but does still offer a certain level of protection.

During the later stages of pregnancy, babies receive passive immunity from their mothers as antibodies developed in the mothers’ bodies travel through the placenta to the babies’ bloodstreams. By this mechanism, babies’ early immune systems are boosted with the help of antibodies from their mothers. Even after babies are born, they can continue to receive antibodies from their mothers through breast milk.

Maternal Immunization

In order to ensure pregnant women have sufficiently high levels of antibodies to pass to their babies or to encourage their immune systems to develop higher levels of antibodies against particular antigens, doctors can use the technique of maternal immunization. If mothers are vaccinated during the second and third trimesters of pregnancy, the exposure to the antigen in the vaccine causes increased production of the appropriate antibody. These extra antibodies will then flow through the placenta to the baby.

Maternal immunization was first used in the 1800s to protect babies against smallpox. Since then, doctors have identified certain vaccines that are particularly effective in protecting newborns when given to their pregnant mothers.

Since passive immunity is shorter-lasting, maternal immunization only boosts a baby’s immune system for about six months after birth. However, by that time, the baby’s immune system has matured further and is more able to fight against infection on its own.

Summary

Since newborn babies don’t yet have a fully functional immune system, they rely on passive immunity that they have received from their mothers in the womb. In order to boost this passive immunity further or target immunity against specific pathogens, doctors may recommend that pregnant women receive certain vaccines during the later stages of pregnancy. The benefits derived from these vaccinations help protect newborn babies until their bodies are better able to defend themselves.