Antibody Levels in Human Milk After COVID-19 Vaccination - An Overview

Introduction

Breast milk acts as a carrier medium through which protective antibodies present in lactating mothers are transferred to their neonates. Scientific evidence proves that virus-specific antibodies (IgA and IgG) are detected in breast milk following SARS-CoV-2 infection in lactating women. However, the impact of various COVID-19 vaccines on lactating women is yet to be analyzed. This article explores various aspects of SARS-CoV-2-specific antibodies in human milk after COVID-19 vaccination. Knowing such scientific facts would empower lactating mothers to make a reliable and efficient decision on getting a suitable vaccination against COVID-19.

What Are the Vaccines Available for COVID-19?

The year 2020 saw the deadliest pandemic outbreak caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This new variant of coronavirus caused more than two million deaths within 14 months of the outbreak and infected more than 100 million of the global population leading to severe illnesses. Following the outbreak, more than 200 vaccine prototypes were formulated and developed against SARS-CoV-2 within a year and were also processed for clinical trials.

Some of the vaccines that were developed for COVID-19 and are effective in controlling the infection are as follows -

• Messenger RNA (mRNA) vaccines such as BNT162b2 mRNA and mRNA-1273.

• Adenovirus-vectored vaccines like ChAdOx1 nCoV-19 were synthesized by combining human genetic vectors with primate adenovirus vectors.

• Inactivated whole-virus SARS-CoV-2 vaccines.

• Adjuvant vaccines such as the Novavax vaccine contain synthetic components as adjuvants.

Although lactating women were not included for safety reasons in COVID-19 vaccination trials, various regulatory organizations and government authorities recommend COVID-19 vaccinations for lactating women who practice breastfeeding because any theoretical risks outweigh the potential benefits induced by maternal vaccination.

What Are the Antibody Levels Seen in Human Milk After Vaccination?

In the initial six months of neonates’ life, their immune system is immature and is in the development process. Hence effective antibody production or response is limited in them. During this phase, the infants are protected through the antibodies transferred from their mothers which they receive during breastfeeding. The secretory immunoglobulin A (IgA) is the predominant antibody present in human milk. It plays a key role as the first line of defense mechanism and in mucosal immunity. The levels of IgA differ widely among lactating women and are dependent on diverse factors such as lactation stages, maternal age, dietary intake, stress, physical activity, and also gestational age (maturity of the baby) at the time of delivery.

Studies have proved that specific SARS-CoV-2 antibodies that are potent against coronavirus (neutralizing efficacy) are present in the human milk of mothers who recovered from COVID-19 illness. Similar antibody responses are induced by COVID-19 vaccinations. The anti-SARS-CoV-2 antibodies present in human milk after vaccination are most commonly IgA and IgG antibodies. The levels of these antibodies widely vary depending on the type of vaccine and also on the number of booster doses. Following are some of the scientific facts about antibody levels that are detected post-vaccination in human milk.

• After vaccination, the anti-SARS-CoV-2 IgA response in human milk is observed but shows wide variability in levels according to the individuals.

• In human milk, SARS-CoV-2 specific IgA starts to increase within five to seven days following the first dose of vaccination with a 12 percent increase per day.

• On the 15th day, a three-fold increase is seen in SARS-CoV-2 specific IgA.

• Following this, its levels gradually decrease until the second booster dose (Day 19 to 36).

• However, the peak level of specific SARS-CoV-2 IgA levels is maintained at 50 percent of the baseline levels.

• This level remains stabilized until three days even after the second booster dose.

• The second booster dose induces a faster response when compared to the first dose.

• The SARS-CoV-2 IgA levels increase by 2.3 times in the first week following the second dose.

• The peak levels are 1.3 times higher after the second booster vaccination when compared to the peak levels of the first dose.

• On the other hand, the serum SARS-CoV-2 specific IgG levels show a sustained and gradual increase. IgG levels do not decline and remain stabilized over a long duration.

• A marked rise in serum SARS-CoV-2 IgG antibodies is seen in the initial two weeks after the first vaccine dose which is stabilized in the following weeks.

What Is the Impact of Anti-SARS-COV-2 Antibodies on Human Milk?

No harmful effects were documented in either lactating mothers or breastfed infants when COVID-19 vaccines are administered to lactating women against SARS-CoV-2. Reports suggest that none of the vaccinations caused any adverse reactions in infants following breastfeeding from vaccinated mothers. Following are some of the reported facts about the influence of antibodies due to COVID-19 vaccination on human milk.

• Antibodies and immune cells (T-cells) that are effective in neutralizing the SARS-CoV-2 virus are seen in human milk after vaccinating the mothers.

• The efficacy of these antibodies (neutralizing capacity) increases even when the level of antibodies drops down.

• Lactating mothers experienced only minimal disturbances in breastfeeding following vaccination.

• Few mothers noticed blue or bluish-green discoloration in their milk during breastfeeding.

• A negligible percentage of babies who were breastfed after vaccination showed signs of sleepiness, higher fussiness, self-limiting diarrhea, rashes, and fever.

• No severe adverse side effects occur in infants if they are breastfed after vaccine administration to their mothers.

• Minimal milk samples from lactating women who were vaccinated with mRNA vaccines contained traces of mRNA. But these levels do not enter into the circulation of the infants.

• mRNA vaccines result in a marked increase of SARS-CoV-2 antibody levels in human milk that are similar to or greater when compared to those levels seen after getting a COVID-19 infection.

• Anti-viral IgG levels in human milk are doubled in mothers who are breastfeeding for 24 months and more when compared to mothers who are breastfeeding for a shorter duration.

Conclusion

The presence of SARS-CoV-2 specific IgA and IgG antibodies in human milk following vaccination plays an important role in protecting babies against COVID-19. These antibodies are effectively transferred through human milk during breastfeeding. This information can help lactating women in making a well-informed decision about whether to get vaccinated.