Breast milk is often referred to as "nature’s perfect medicine" for good reason. Packed with essential nutrients, human milk oligosaccharides (HMOs), and bioactive compounds, it offers unparalleled protection and nourishment for infants. But as more families turn to donor milk and ask questions about vaccines, viruses, and overall safety, ensuring that breast milk stays pure and protective has never been more important. Let’s dive into what really transfers through breast milk, including COVID-19 virus itself as well as the vaccines, and why testing donor milk is crucial for your baby’s health.

understanding breast milk’s nutritional power

Breast milk is a dynamic and complex substance. Its components can adapt to meet the unique needs of your baby, transferring beneficial nutrients and bioactive compounds. Here's a snapshot of what makes breast milk essential:

1. Nutrients: Breast milk provides proteins, fats, carbohydrates, vitamins, and minerals essential for growth and brain development. Examples: Lactoferrin (supports gut health), DHA (supports brain development).

2. HMOs (Human Milk Oligosaccharides): These specialized carbohydrates are critical for developing your baby’s gut microbiome. HMOs promote the growth of beneficial bacteria while preventing harmful pathogens from taking hold.

3. Microbiome Development: Breast milk helps establish a healthy gut microbiome in your baby, which is essential for digestion, immune function, and overall health.

However, not everything passes through breast milk—and understanding what does is key to protecting your little one.

COVID-19: How the Virus and Vaccine Interact With Breast Milk

One of the most common concerns we hear from parents today is about the transferability of COVID-19—whether from infection or vaccination—into breast milk. Here's what the science says:

COVID-19 Virus vs. Vaccine: Understanding the Spike Protein

Both the virus and the vaccines rely on the same spike protein to stimulate your immune system, but they interact with your body in very different ways:

1. The COVID-19 Virus: When someone is infected with COVID-19, the virus enters the body and uses the spike protein to attach to and invade cells. Once inside, the virus replicates, spreading throughout the body and potentially causing damage to organs and systems. The body eventually produces antibodies against the spike protein and other parts of the virus to fight off the infection.

2. The COVID-19 Vaccines: The vaccines, on the other hand, contain only a small snippet of mRNA that provides instructions to your cells on how to make the spike protein temporarily. Importantly, the mRNA never enters the nucleus of your cells (where your DNA is stored), and it is quickly broken down after its job is done. Your body recognizes the spike protein as foreign and produces antibodies to fight it. Unlike the virus, the vaccine doesn’t replicate or spread—it simply teaches your immune system how to respond if you encounter the real virus in the future.

Key Difference: The virus actively invades and damages cells during an infection, while the vaccine cannot enter cells or cause illness. 

What Passes Into Breast Milk?

• From the Virus: If a breastfeeding mother has COVID-19, viral RNA fragments may be present in breast milk, but these are not infectious. Antibodies produced by the mother’s immune response do transfer into the milk, offering protection to the baby.

• From the Vaccine: The mRNA from the vaccine does not enter breast milk. However, the antibodies generated by the mother’s immune response do pass into the milk, providing the same protective benefits without exposing the baby to the virus.

Key Takeaway: There is no meaningful difference in the protective antibodies transferred to breast milk whether they come from a natural infection or a vaccine. Both provide benefits for the baby’s immune system.

why testing donor milk is non-negotiable

When it comes to donor breast milk, ensuring purity and safety is critical. While breast milk is a natural miracle, contaminants like certain viruses, bacteria, or medication residues can pose serious risks to infants if left untested. For example:

• Untested donor milk may contain harmful bacteria like E. coli or pathogens like Staphylococcus aureus, which can cause severe health complications in babies.

• Infants fed untested milk may also be exposed to medications or substances that are not safe for their age and development.

• Certain virus groups, such as retroviruses (e.g., HIV) and herpesviruses (e.g., CMV), can be transmitted through breast milk. These viruses persist in bodily fluids or reactivate during infections, posing a possible risk to infants, which can lead to life-altering health outcomes.

At Leche, we prioritize safety by rigorously screening all donor milk. Each batch undergoes extensive testing for bacteria, viruses, and quality assurance, ensuring your baby gets only the best.

For more on why donor milk testing matters, read our article here.

the risks of untested donor milk

If donor breast milk isn’t properly screened, here’s what could potentially transfer to your baby:

1. Harmful Bacteria: E. coli, Staphylococcus aureus, and other dangerous bacteria can cause infections and severe health problems in infants.

2. Blood-borne pathogens: Blood borne pathogens like CMV (cytomegalovirus) or hepatitis can be present in untested milk.

3. Medications or Substances: Traces of prescription drugs or other substances the donor may have consumed.

This is why using donor milk from an unverified source is never worth the risk. Protect your baby’s health by choosing a trusted provider like Leche, where every drop of milk is tested and safe.

ensuring the purity of breast milk in a post-pandemic world

Whether you’re a breastfeeding mom or rely on donor milk, ensuring the purity and safety of breast milk is the best gift you can give your baby. Here are some tips:

• Stay Informed: Understand what transfers through breast milk and make informed decisions about vaccinations and donor milk.

• Choose Tested Milk: Always opt for milk from a provider that screens and tests for safety and quality, like Leche.

key takeaways

Breast milk is an incredible resource for nourishing and protecting your baby, whether it comes from you or a donor. Understanding what transfers through milk—from nutrients to HMOs and microbiome support—empowers you to make informed choices about your baby’s health. With rigorous testing and screening, we can ensure that breast milk remains nature’s perfect medicine.

For more information about safe, tested donor milk, and the benefits of freeze-drying your milk, visit Leche.