Pregnant and breastfeeding women have been excluded from all clinical trials with new messenger ribonucleic acid (mRNA) vaccines against the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The presence of anti-SARS-CoV-2 antibodies in breast milk and its immunological protection are well known.
A new study published in BMC Pregnancy and Childbirth studies the presence of antibodies in breast milk and the immune responses of lactating women compared to non-lactating women after vaccination using the BNT162b2 Pfizer-BioNTech vaccine.
To study: COVID-19 mRNA vaccine and antibody response in lactating women: a prospective cohort study. Image Credit: Pixel-Shot / Shutterstock.com
Vaccination and breast milk
Newborns have an immature immune system. During the first months of life, they receive immunological protection through breastfeeding.
Several characteristics of breastfeeding mothers can affect the presence of antibodies in breast milk. Some of these may include previous infections, age, genetic factors, and immunity.
Breast milk contains secretory immunoglobulin A (IgA) (SIgA), IgM, and IgG antibodies. SIgA represents 90% of the antibodies present in breast milk and is essential for the defense of the mucous membranes.
The American College of Obstetricians and Gynecologists said breastfeeding women should be offered vaccines for coronavirus disease 2019 (COVID-19). Additionally, the Academy of Breastfeeding Medicine does not recommend that breastfeeding women stop breastfeeding after receiving the COVID-19 vaccine.
There are no data on the potential risks or benefits for babies breastfed by women vaccinated against COVID-19. However, vaccination against influenza during pregnancy causes the production of specific antibodies by breastfeeding. The same principle can be extrapolated to mRNA vaccines.
A previous study of 31 breastfeeding women suggests that COVID-19 mRNA vaccines elicit humoral immune responses in breastfeeding women that are comparable to those seen in non-pregnant populations. This study also confirmed the presence of anti-SARS-CoV-2 IgG antibodies present in breast milk.
In the present study, the researchers aimed to determine the blood antibody profile of breastfeeding women compared to non-breastfeeding women after vaccination with the Pfizer vaccine. Additionally, the researchers wanted to determine if the antibodies could be transferred to the infant through breast milk.
Measurement of antibody response after vaccination
In the current prospective cohort study, 24 healthcare workers were included, of whom 14 were breastfeeding and 10 were not. All eligible participants were vaccinated with the BNT162b2 Pfizer vaccine.
Clinical data related to demographics, date and type of delivery, breastfeeding details, timing of COVID-19 vaccine doses, and post-vaccination symptoms were recorded through a written questionnaire. .
A blood sample was taken from all participants one to three weeks after receiving the first and second doses of vaccination. Simultaneously, breast milk was collected from lactating women on the same days.
Anti-SARS-CoV-2 antibody levels, including peak IgG, IgA, and IgM, were quantified in blood and breast milk after vaccination. Antibody quantification was performed by enzyme immunoassay (ELISA) on SARS-CoV-2 trimeric spike protein.
Post-vaccination antibodies in serum and breast milk
Breastfeeding and non-breastfeeding women showed no difference in terms of age, smoking habits, comorbidities and post-vaccination side effects. Additionally, none of these participants reported prior SARS-CoV-2 infection.
All women developed immunity after vaccination and showed positive serum IgM, IgA and IgG antibodies after the second dose. IgG levels were dominant in lactating and non-lactating women. However, non-breastfeeding women had higher levels of IgG antibodies after the first dose. In lactating women, IgM and IgG antibodies increased after the 2nd dose.
Breast milk from lactating women showed modest levels of antibodies, particularly IgG at 42.9%. Notably, elevated IgG levels were associated with longer breastfeeding duration, although this association was moderate.
No antibody testing was done prior to vaccination. Therefore, it is possible that the participants were previously infected with SARS-CoV-2.
However, since the participants were health workers, they were systematically tested and none of them reported any previous infection. Notably, the sample size included in this study was small; therefore, the results cannot be generalized.
More than 90% of the population has antibodies against at least three human coronaviruses. The possibility of cross-reactivity in antibody testing cannot be denied.
Implications of the study
Not much is known about COVID-19 vaccination and breastfeeding. Additionally, there is also little evidence indicating the transfer of antibodies into breast milk following vaccination against COVID-19.
This is the first study to link breastfeeding duration to higher levels of antibodies in breast milk. Although the presence of antibodies in breast milk is reported, vaccination through breastfeeding has not yet been verified. Thus, additional clinical studies are needed in breastfeeding women to meet scientific recommendations.