Pregnancy, Breastfeeding, and the COVID Vaccine
A spectrum of opportunity.
Most of you know that pregnant and breastfeeding people were not included in the original mRNA vaccine studies. Since the EUA was issued, however, thousands of pregnant and lactating front-line workers have chosen to be vaccinated. We are starting to see data suggesting what we originally suspected - mRNA vaccines are well-tolerated and provide exceptional protection against severe disease and death. In addition, there are early reports of immunity being passed to the fetus through the placenta and to nursing infants through human milk.
This is all good news.
Knowing we can leverage parental COVID vaccination to protect our infants is an incentivizing bonus to getting the vaccine. I’ve been talking with parents, however, who are losing sleep over the “best” time to get vaccinated during this pregnant-to-lactating life spectrum. Some families have even deferred opportunities to get vaccinated (Nooooo!) based on an unclear understanding of how immunity is transferred from parent to child, or have passed on protection because they were told it was “too late.”
As a pedi who cares deeply for the health and safety of my pregnant parents and their progeny, hearing stories of families declining vaccines as a result of patchy or delusive information upsets me. That being said, the goal of this letter is not to persuade or convince anyone to accept the vaccine if it does not feel right. Each pregnant person needs to make a judgement on whether or not to get vaccinated based upon her personal risks. Rather, I am hoping a quick dive into basic immunity science will add clarity to how the COVID vaccine directly and indirectly supports infant protection throughout pregnancy and beyond, increase confidence in your vaccine decision, and limit the hand wringing this whole topic may bring.
Long-term immunity is the result of an active process.
Let’s start by dividing immunity into two broad categories, active and passive. Active immunity is the kind of immune defense that is triggered by natural infection or vaccination. After the body identifies an infectious target, our healthy immune system activates a regiment to create an army of antibodies, additional infection-fighting cells, and anti-inflammatory agents. The production process is not immediate, taking days to weeks for optimal protection. But for the cost of this manufacturing delay, there is a bonus - memory cells are created as part of the immune army. These special cells can remember antibody “blueprints,” allowing for quick action against future pathogen attacks. Gaining the benefits of this diverse and dynamic infection protection, with its memory cell magic, can only happen by activating the immune system to do the work.
Human milk is a source of passive immunity.
When infants receive immune protection though the placenta or human milk, it is via passive immunity. This process is exactly what it sounds like - accepting pre-made antibodies from another source. The recipient receives immediate protection from these artificial antibodies without having to do any immune system “work.” In the case of human milk, the infant passively consumes the antibodies. During pregnancy, working antibodies are exchanged over the placenta. Things like monoclonal antibody therapy, immunoglobulin injections, and convalescent plasma are also types of passive protection against disease.
As much as all these types of passive protection are potentially life-saving to those who receive them, their effect is only temporary. Pre-made antibodies are either used or degraded by the recipient in short order. For example, maternal antibodies are detected in infant blood for 6-12 months after birth. And after nursing, the consumed antibodies live in the gut and respiratory tract a few days to weeks before being degraded or replaced. Passive immunity is valuable, but fleeting. And it never results in the long-term protection that active immunity can provide.
With this framework in mind, it becomes clear that the COVID vaccine is providing direct, long-term protection to a pregnant adult, both during the pregnancy and into the postnatal period. If you plan on getting the COVID vaccine and are eligible to receive it, don’t undervalue the importance of protecting yourself first. Pregnancy is a high-risk condition and a severely ill parent cannot bond, feed, or effectively care for a newborn. There is no benefit in delaying vaccination, and current CDC and ACOG guidelines allow pregnant individuals to receive the vaccine throughout all stages of pregnancy.
The value of parental vaccination to an infant changes over time.
Under the all-encompassing umbrella of maternal protection, the direct benefit of vaccination to the infant changes from early pregnancy through the infancy period. After a pregnant person’s antibody levels rise, maternal antibodies will begin to cross the placental barrier to the fetus. This is the only way infants will receive significant levels of blood-circulating antibodies from their mother and the bulk of placental transfer occurs during the third trimester. ** As a result, completing the mRNA vaccine series prior to pregnancy or by the third trimester is optimal for this type of protection.
Getting vaccinated later in pregnancy still offers advantage. In addition to transferring as much maternal antibody as possible for the remaining weeks in the womb, vaccination offers the ability to get secretory antibodies into maternal colostrum and breast milk. Colostrum, the nutrient dense first milk produced, is packed full of secretory antibodies. After ingestion, these immune proteins line the inside of the gut and respiratory tract, acting as a physical barrier to all sorts of infections and priming the infant’s immune system for defense. Colostrum transitions to more mature breast milk over time, offering a continuing supply of this type of protection until a child is weaned.
For as long as a parent wishes to provide human milk, the secretory immune benefits are passively received by the infant. It is a common misconception, however, that a significant amount of antibody is “absorbed” by the child from human milk or that ingesting human milk provides the same long-term disease protection as a vaccine. Unfortunately, this is not true. Although it is well-known that human milk provides a living team of cells and proteins that protect the infant from all sorts of bacteria and viruses, secretory antibodies in human milk are not absorbed by the infant to any significant extent nor does ingesting breast milk induce an active immunity cascade. This does not minimize the diverse biological and psychological benefits that breastfeeding can provide. But, it may provide support for mothers who have reached personal breastfeeding goals and are ready to wean, or reassure parents of formula-fed infants that maternal immunity has already been passed to their baby in utero.
Even If you are not pregnant or lactating, parental vaccination offers children benefits. Currently, most young children are not suffering from COVID-19 disease as much as adults. For children who do get infected, however, a common source is an infected family member. By getting vaccinated, a parent is both protecting herself from severe disease and limiting the spread of the virus to her children. In this way, vaccinating a parent creates a “cocoon'' of protection for all the children in the home and a critical layer of disease defense for the entire family.
Safely passing SARS-CoV-2 antibodies to newborns and infants via parental vaccination is great news and a continuing area of research. By vaccinating pregnant people and nursing parents, we can increase the bubble of protection around our babies and add another layer of reassurance to our families. Based on the information we have today, I continue to support pregnant and lactating people get vaccinated with either mRNA vaccine, if recommended by their personal physicians. And I encourage all parents to continue asking their pediatricians questions about vaccines. These conversations are insightful, important, and impactful as we continue to fight against this Pandemic and other vaccine-preventable illnesses.
Looking forward,
**An important caveat: Not all types of maternal antibodies cross the placenta. Although we have early studies that have identified SARS-CoV-2 antibodies in newborns, we do not know if those antibodies are, in fact, neutralizing. In addition we don’t know the quantity of antibody needed for direct infant protection. Studies are ongoing and I’m eager to hear positive news.
Special thanks to my colleague, Dr. Maddie Summers, who added valued editorial support to this letter.
Great information! Thank you for sharing (and for incorporating BOTH Hamilton and Schitt's Creek GIFs into your post)!