Long-term Pfizer vaccine-induced SARS/CoV-2 antigen profile was detected in breast milk

Although the overall safety of coronavirus disease 2019 (COVID-19) vaccines in pregnant women appears to be supported by available post-vaccination data A new study that was published on the preprint server medRxiv*appears to suggest that the Pfizer vaccine produces antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These antibodies can be passed into breast milk and protect the baby for up to six months after the date of vaccination.

Study: Quantification and progression over time of specific antibodies against SARS-CoV-2 found in breast milk of lactating women vaccinated with BNT162b2 Pfizer-BioNTech COVID-19 vaccine (LacCOVID). Image Credit: evso /


The current study was designed to determine the antibody titers of breast milk from women who were breastfeeding for one month after receiving the messenger ribonucleic substances (mRNA) Pfizer/BioNTech vaccination for COVID-19. They also wanted to determine the levels of maternal serum specific antibodies were associated with the concentrations of antibodies in breast milk.

The researchers of the study also examined the efficacy of the vaccine and the adverse reactions that are associated with vaccination of infants or mothers. This is the first long-term and long-term study of the levels of antibodies in breast milk following administration of this vaccine.

The current study included 33 mother-infant couples, with a median age between 38 and 15 months for the infants and mothers. None of the participants were positive for the infection at the beginning of the study. There were 32 and 28 participants following the first and second dose, respectively, while eight quit the study after six months.

There were total 149 serum and milk samples. The median time for the first set was two weeks following the first dose and the second set was 14 days following the second dose. The third sample was obtained 28 days from the second dose and the fourth was taken at 12 weeks, whereas the final sample was taken 24 weeks following the second dose.

Research results

The researchers found that, at two weeks after the second dose, the median anti-spike S1 immunoglobulin G (IgG) antibody levels were highest in both milk and serum with a parallel progression from the earliest time point in their rise and fall, though separated by a large margin.

The most frequent adverse reactions related to vaccinations were local injection site pain which was reported by nearly all women. However, fever, malaise and headaches were only present in one percent. Other common symptoms of the system were reported by a tiny proportion of mothers, with no visible effects in the infants.

Two mothers developed breakthrough SARS-CoV-2 infections, one unasymptomatic, and diagnosed in retrospect and the other having mild. In the first instance, IgG-S1 levels were found to be significantly elevated in both milk and serum, in comparison to the previous fourth sample. In addition, anti-nucleocapsid antibodies, which aren’t generated by the vaccine spike antigen are present in serum but not milk.


Fears surrounding the potential ability to breastfeed can result in vertical transmission of the virus from mothers who are infected and, in the case of the vaccine that it could harm the baby or fetus during breastfeeding and pregnancy, respectively. This led to a lack of evidence-backed guidelines on breastfeeding practices following vaccination of lactating mothers, or even the necessity of vaccination for this group.

Because the vaccine wasn’t tested on pregnant or nursing women in clinical trials post-marketing monitoring is the main source of information on the safety of vaccines. This led to LacCOVID, which used information from frontline workers who were lactating who had received the vaccine in the early stages.

The present study confirms that specific antibodies to SARS-CoV-2 exist in the breast milk of vaccine-vaccinated women. This is in line with studies conducted in the past that were short-term. This is, however, the first study to run for six months.

While the levels of antibodies in serum decrease over this time period according to available information from other research reports, the findings here indicate that breast milk samples have declining levels of antibodies at the age of three and six months, also in line with serum levels.

It is reasonable to think that the serum test for SARS-2 IgG–S1 might indicate approximately the amount of antibodies present in breastmilk six months after vaccination..

The transplacental transmission of protective antibodies against the virus is linked to the pregnancy vaccination using an mRNA-based vaccine. This confers immunity over the period of neonatal development. This study also shows that infants are protected for at least six more months if they have been vaccinated in the first six months after birth.

This conclusion is not supported by the two cases of breakthrough infection within this small sample, both after three months since the date of vaccination, which suggests a relatively high incidence among healthcare professionals. This is in addition to the protection effectiveness of these antibodies within the infant.

The study also demonstrated that even at high levels the anti-nucleocapsid antibody fails to be detected in breast milk. The study also suggests the potential use of booster shots in this group. In both instances the breakthrough infections were associated with an increase in antibody titers breast milk and serum.

Larger samples will be required to verify and expand on these findings following the use of mRNA and other vaccines, and also using various antibody detection methods. The protective efficacy of these antibodies in breast milk is also required to be evaluated.

The current study confirms the safety of the Pfizer vaccine during lactation, and also the presence of specific antibodies in breast milk six months after vaccination, with a late decline. If the vaccine is found to be safe and prevents transmission of the virus to infants through both group immunity and antibodies in breast milk.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

Gemma Wilson

Gemma is a journalism graduate with keen interest in covering business news – specifically startups. She has as a keen eye for technologies and has predicted quite a few successful startups over the last couple of years.

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