Feature Article: Are Infant Immune Systems Overwhelmed by Vaccines?

It’s a common concern among parents of newborns and infants — are my kids getting too many vaccines? Are the vaccines overwhelming their immune system? Indeed, the recommended childhood vaccine schedule includes 26 inoculations against 14 vaccine-preventable diseases during a child’s first two years of life. The well visits during which children receive these vaccines can include up to five shots.

Yet both the cumulative effects of the childhood vaccine schedule and the volume of shots given during a single visit shouldn’t be the basis for lingering doubts. Anytime these concerns have been studied, the data have been reassuring.

Immunologic challenges posed by vaccines

Immunological components of vaccines are the viral or bacterial proteins or bacterial polysaccharides (complex sugars) contained in a vaccine that induce an immune response. In the 1980s, children received vaccines to protect them from seven diseases: diphtheria, tetanus, pertussis, polio, measles, mumps and rubella. Immunological components contained in these vaccines numbered about 3,000. Currently, the recommended immunization schedule protects children from 14 diseases, and the total number of immunological components is between 150 and 160, depending on which versions of the pertussis and rotavirus vaccines children are given. So in approximately 30 years, the protection children receive against vaccine-preventable diseases has doubled — from seven diseases to 14 — while the immunological challenge has decreased almost 95 percent.

The environment in which infants grow

Another important consideration is that infants do not live in a sterile environment. Babies face immunological challenges ever-present in the environment around them;  food, water, air, toys, surfaces and other people are all non-sterile and, therefore, are potential sources of germs that could cause their bodies to generate immune responses. While their immune systems need time to mature, the truth of the matter is the immunologic challenges presented by vaccines are minimal when compared with the number of viruses and bacteria infants successfully manage every day. Shortly after birth, newborns are exposed to trillions of bacteria — carrying them on their skins and mucosal surfaces (nose, throat, intestines). In order to avoid infection, babies’ immune systems constantly make antibodies — the product of an immunological challenge.

This concern, that infants’ immune systems are immature, has merit within context. That is, studies have shown that infants’ immune systems are not as good at making T cell responses as those of older infants and children. Likewise, B cell responses, responsible for generating antibodies against the complex sugars on the surface of bacteria, take time to mature. However, it does not mean that infants are completely incapable of protecting themselves. Indeed, if this were the case, our species would cease to exist. However, humans have evolved to endure in a few ways:

1. Maternal antibodies that crossed the placenta during gestation and those present in breast milk protect infants in the first few months of life while their immune systems mature. These antibodies only last for the first few months of life.
2. Unless infants have a specific immune deficiency, they are generally able to make some level of immune response — either non-specific or specific. So, while infants are more susceptible to certain diseases, they are not without tools to resolve infections. Vaccines help by introducing weakened versions of some higher-risk pathogens, so that infants’ immune systems can begin the process of developing immunity. These vaccines are added to the schedule so that by the time infants are most susceptible — because protection from moms’ antibodies has decreased and their immune system is still maturing — they have developed protective immunity from the vaccinations. In this way, vaccines are like “hedging one’s bets” — the infant’s young immune system may work well enough on its own, but by educating it with the vaccines, it is more likely to get the job done without the baby suffering the consequences of natural infection.

Additional resources

• VEC: Vaccine and the immune system Q&A