A recent study by researchers from Poland, published in the journal Vaccines, shows how levels of IgA and IgG antibodies specific to the spike glycoprotein of SARS-CoV-2 increase in both breast milk and serum samples of mothers following vaccination against coronavirus disease (COVID-19) – with important implications for further vaccine planning endeavors.
The ongoing COVID-19 pandemic is currently being tackled with an unprecedented global vaccine rollout. Basically, vaccines against COVID-19 are designed to trigger the natural production of antibodies in the human body, as well as to stimulate the immune cells to confer adequate protection.
However, when the vaccination program started, there was a lack of data on the safety of the COVID-19 vaccine in lactating women, but also its effects on milk production, milk excretion and the breastfed child. Nonetheless, specialists endorsed the messenger RNA (mRNA) vaccines as safe for both breastfeeding mothers and their babies.
The reason was the fact that the mRNA vaccine carries only the genetic information needed for the synthesis of the SARS-CoV-2 spike glycoprotein. This means that it does not contain a weakened virus or a virus with the potential to replicate, as is the case with many older vaccines. Thus the risk of adverse events is significantly reduced.
Still, as the US Food and Drug Administration (FDA) recommended leaving the decision on vaccination against COVID-19 to the women themselves, the aim of this study (conducted by researchers from the Wroclaw Medical University in Poland) was to appraise the immune response to COVID-19 vaccination in breastfeeding women and possible advantages for both mother and child.
A methodological approach
The study population involved 32 breastfeeding women who previously decided to take the vaccine due to their employment in the health care sector and subsequent occupational risk of contracting COVID-19. There was also a control group that entailed 28 breastfeeding, non-vaccinated women.
The Pfizer-BioNTech mRNA vaccine BNT162b2 was used, which encodes the SARS-CoV-2 full-length spike glycoprotein. It was given intramuscularly in two doses (21 days apart) according to the local regulations and product characteristics.
Both serum samples and breast milk samples were collected in designated periods after vaccinations. The concentrations of anti-SARS-CoV-2 IgG, IgM and IgA antibodies have been measured with the use of quantitative enzyme-linked immunosorbent assay (ELISA)
High level of antibodies in serum and breast milk
In short, a strong secretion of SARS-CoV-2-specific IgA and IgG antibodies has been detected in breast milk for six weeks after vaccination. Furthermore, the breast milk IgG level was detectable and highly correlated to IgG levels in the serum samples.
Both the IgG and IgA antibodies significantly increased in the serum and breast milk following the vaccination – with the highest concentrations of all antibodies on day 29 after the first vaccine dose and a decrease on day 43. The type of breastfeeding did not influence the level of antibodies in breast milk.
As antibodies against SARS-CoV-2 previously detected in the breast milk of women infected with COVID-19 demonstrated strong neutralizing effects, implying a potential protective effect against infection in the infants, the same can be expected after vaccination.
Implications for vaccination of breastfeeding women
This study provided indispensable information for improved understanding of the immune response to a COVID-19 vaccination in breastfeeding women, but also its possible effects down the line on the breastfed child.
As there were no serious side effects in the children after the mothers’ vaccinations, and the presence of IgG and IgA antibodies in the breast milk was shown, the study gives further evidence on the importance of vaccination against COVID-19 in breastfeeding women”, say the authors of this study.
Consequently, future recommendations for COVID-19 vaccination in the general population of breastfeeding mothers should take these results into account. However, as the neutralization capacity of IgG and IgA has not been evaluated, there is a need to appraise whether lactating mothers can actually transfer protective antibodies to their nursing infants.
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