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Home » Breastfeeding cannot replace a vaccine – let’s talk about passive immunity

Breastfeeding cannot replace a vaccine – let’s talk about passive immunity

Last updated on April 1st, 2021 at 10:48 am

One of the pervasive myths expressed by the anti-vaccine world is that one or all childhood vaccines can be replaced by breastfeeding. Somehow, these people believe that breast milk is such a powerful agent of the immune system that vaccinations are unnecessary. But that’s not based on any science related to human physiology, especially with respect to the immune system.

These beliefs represent a misunderstanding of how our immune system functions, especially regarding the role of passive immunity. Breastfeeding, of course, has a lot of benefits to both the developing baby and the mother. But we shouldn’t endow it with magical qualities, especially with regards to how it operates with the infant’s own immune system.

I want to take some of your time here to give a condensed version of immunology, especially the differences between passive and adaptive immunity. And I want to show how breastfeeding complements the developing baby’s immune system. 

Immune system basics

Immunology is a branch of biology that includes the study and research into the immune systems of every living organism on the planet. In medicine, of course, immunology focuses on the human immune system.

Human immunology is a subject that requires years of classwork and research along with reading mountains of papers. I’ve tried to synthesize our understanding of the immune system in an article earlier in 2018, so if you’re interested in getting some ideas about the immune system, it could be a good start.

The human immune system is an incredibly complex interaction of organs, cells, proteins, and other factors that are constantly protecting us from literally millions of different bacteria, viruses, and other things every day. There are scientists that focus their whole career in examining just one of those interactions – oversimplifying our immune system by saying that all we need to do is drink a blueberry kale shake will “boost” our immune system against infectious diseases, cancer, and old age. It doesn’t worth that way.

So how does it work? Let’s go with a quick primer on the immune system.

The immune system is broken down into two parts with totally different functions and physiology – the innate and the adaptive, or active, immune systems. Although they work with each other, they are separate.

The innate immune system is more of a generalist system lacking the ability to selectively attack specific antigens. This part of the immune system includes its ability to prevent or detect foreign material, then eliminate it without an antigen- or pathogen-specific physiological response of the body. It is the body’s quick and initial general response to disease-causing organisms (pathogens) which invade our body.

The innate response works in one of two ways: first, it directly prevents an infection, such as the skin blocking bacteria from entering the bloodstream. And second, it delays the invasion sufficiently for the slower but more effective and selective adaptive Immune system to activate its response to the pathogens.

Anatomical barriers, like the skin or the highly acidic stomach, inflammatory responses, activation of the complement cascade, and white blood cells make up most of the innate immune system.

As the title of this article implies, breastfeeding is important to the story of the passive immune system of a developing baby. We’ll get to that in a bit.

The adaptive, or active, immune system is the second, and possibly more powerful, part. Basically, when the passive immune system encounters a pathogen, it sends a signal to activate the adaptive immune system. This part of the immune system is composed of highly specialized systemic cells and processes that eliminate pathogens.

Antibodies, produced by B-lymphocyte cells, are the main weapon of the body’s immune system to battle pathogens. Antibodies form a larger, more powerful, response than passive immunity. Moreover, this system, once sensitized to an antigen like on the surface of a virus or bacteria, “remembers” that antigen, and then it can fight the pathogen years later when it encounters it. It does this often before the pathogen can present with symptoms of a disease.

The adaptive immune system is highly specific and needs to “learn” the antigens on new pathogens. This takes time, so the viral or bacterial pathogens can invade cells, damage organs, and cause harm while the immune system is gearing up. No matter how much you want to believe it, you cannot eat GMO-free, organic, sun-splashed orange juice 10 times a day to speed up or boost the immune system. That is a myth.

A baby or adult that encounters pathogen A doesn’t suddenly develop a more powerful immune system to deal with pathogen B. The adaptive immune system has to start all over to deal with the second pathogen. So getting a “natural” immunity to chickenpox doesn’t suddenly make the immune system of the child or adult become more powerful against the measles.

Knowing all of this, vaccines work by introducing a pathogen’s antigen to the adaptive immune system so that it can form that pathogen-specific response well before encountering the pathogen. More importantly, it trains the active immune system, with dead or disabled viruses and bacteria, to recognize the pathogen’s antigens without risk of the pathogen causing an infection. And once again, this adaptive immune response, induced by vaccines, remember the pathogen’s antigens for years or decades.

Unless you have a serious immune deficiency or chronic malnutrition, there’s really no way to “boost” the immune system, especially the adaptive portion of it. Actually, the only way to “boost” that immune system is with vaccines.

That is a very brief overview of the immune system, and I’m sure a real immunologist will laugh at my primer. If there is one lesson I could preach about this topic is that the immune system is almost impossibly complex – the thought that any of us can make it do our bidding with a few supplements or food is pretty naive.

But we’re here to discuss breastfeeding and passive immunity, so let’s get to that.

Passive immunity – maternal antibodies

In infants, there is a version of the innate immune system called passive immunity. During pregnancy, maternal antibodies produced by the mother’s own adaptive immune system can be transported across the placenta into the fetal blood supply. These antibodies are called immunoglobulin G, or IgG – they are the only one of the five classes of antibodies that can cross the placental barrier.

Immunoglobulin G is the most common class of antibodies in our bodies. They are responsible for protecting us against bacteria and viruses through several biochemical interactions:

  • They immobilize and clump together pathogens so that they can be destroyed by certain phagocytic immune cells allowing the body to rid itself of those pathogens.
  • They can eliminate pathogens directly,
  • They can bind and neutralize toxins produced by pathogens.
  • They can directly kill cells.

Upon birth, babies have all the IgG’s that they will ever get from the mother. They will not get any more of them from the mother, including from breastfeeding. And those IgG’s do not reproduce themselves or train the baby’s immune system to produce them.

Maternal IgG antibodies are temporary, however, and gradually disappear within about 6-8 months after birth. During those months, the baby begins to develop its own adaptive immune response and produces IgGs in response to pathogenic viruses and bacteria that they encounter. By six months, all of the maternal IgG antibodies are gone, and all of the remaining IgGs are from the baby. During this time, when babies receive vaccines, they begin to produce their own antibodies to those vaccine-preventable diseases.

Furthermore, this is why pregnant women should consider getting important vaccinations, like for pertussis, because they boost the level of these maternal antibodies so that they can be passed to the fetus. And a fully vaccinated mother can protect their newborn against diseases that can be dangerous, even deadly.

Passive immunity and breastfeeding

The second type of passive immunity for a newborn is from breastfeeding. Colostrum, the first breast milk a mother produces when she begins to breastfeed, contains a huge quantity of immunoglobulin A or IgA. These are called secretory immunoglobulins because they are produced by mucosal membranes, like those that line the gut.

These IgA’s are not absorbed by the baby (see Note 1) into their bloodstream. Those IgA antibodies work within the newborn’s digestive tract to protect it against infections that could attack there. These IgAs protect the mucous membranes in the baby’s mouth, throat, and intestinal tract. This type of passive immunity continues until the baby stops breastfeeding.

It’s also important to reiterate a couple of points. This is not another form of adaptive immunity – the baby doesn’t retain this immunity once breastfeeding stops. Second, like with IgG, these IgA antibodies from the breast milk do not induce the baby to produce new IgAs. The effect only lasts while breastfeeding – the baby can produce its own IgAs within a few days or weeks.

And we need to make something very clear – although this type of passive immunity is critical to the baby, it only protects against pathogens that attack in the digestive tract. It does not provide a shield against vaccine-preventable diseases that enter the bloodstream. After the maternal IgG antibodies disappear after a few months (and are not replenished by breastfeeding), the baby is susceptible to those diseases.


Too many mothers endow breastfeeding with miraculous properties that just don’t exist. I’ve frequently heard the claim that infants don’t need vaccines because breast milk gives the baby everything it needs to protect them from vaccine-preventable diseases.

Again, breastfeeding has many benefits to newborn – the science on that is clear, if not overwhelming. But it is not a replacement for vaccines. Given our rather thorough understanding of breast milk and the baby’s immune system, we can conclude two things:

  1. That mothers should strongly consider following vaccination recommendations during and after pregnancy, to provide critical IgG antibodies to the fetus.
  2. That breastfeeding is not a replacement for the recommended vaccination schedule for babies.

I think the way we should look at this is that breastfeeding and vaccines go hand-in-hand. The baby is much better off, from an immune standpoint, with both.


  1. I need to clear up another myth about digestion. Almost everything one consumes, including a baby, is broken down into simpler molecules. For example, proteins, like IgG or IgA, do not pass from the intestinal tract to the bloodstream intact. They are broken down into constituent amino acids, which can then move into the bloodstream and used by the body to produce new proteins. The same happens to carbohydrates, which are broken down into one of four simple sugars. Everything you eat is broken down into very simple biochemicals – you hardly ever absorb the full-sized biochemical in any of your food.


Michael Simpson

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