COVID-19 booster enhances IgG mediated viral neutralization by human milk in vitro

Background

Facilitated by the inability to vaccinate, and an immature immune system, COVID-19 remains a leading cause of death among children. Vaccinated lactating mothers produce specific SARS-CoV-2 antibodies in their milk, capable of neutralizing the virus in vitro. Our objective for this study is to assess the effect of COVID-19 booster dose on SARS-CoV-2 antibody concentration and viral neutralization in milk, plasma, and infant stool.

Methods

Thirty-nine mothers and 25 infants were enrolled from December 2020 to May 2022. Milk, maternal plasma, and infants' stool were collected at various time-points up to 12 months following mRNA COVID-19 vaccination. A subgroup of 14 mothers received a booster dose. SARS-CoV-2 antibody levels and their neutralization capacities were assessed.

Results

Booster vaccination led to significantly higher IgG levels within human milk and breastfed infants' stool. In vitro neutralization of VSV-gfp-SARS-CoV-2-S-gp, a laboratory safe SARS-CoV-2 like pseudovirus, improved following the booster, with a 90% increase in plasma neutralization and a 60% increase in milk neutralization. We found that post-booster neutralization by human milk was highly correlated to SARS-CoV-2 IgG level. In support of our correlation result, Protein G column depletion of IgG in milk yielded a significant reduction in viral neutralization (p = 0.04).

Discussion

The substantial increase in neutralizing IgG levels in milk and breastfed infants' stool post-booster, coupled with the decrease in milk neutralization capabilities upon IgG depletion, underscores the efficacy of booster doses in augmenting the immune response against SARS-CoV-2 in human milk.

Detection of SARS-CoV-2 IgA and IgG in human milk and breastfeeding infant stool 6 months after maternal COVID-19 vaccination

OBJECTIVE

Assess presence, durability, and neutralization capacity of SARS-CoV-2-specific antibodies in breastfeeding infants' stool, mother's plasma and milk following maternal vaccination.

DESIGN

Thirty-seven mothers and 25 infants were enrolled between December 2020 and November 2021 for this prospective observational study. All mothers were vaccinated during lactation except three, which were vaccinated during pregnancy. Milk, maternal plasma, and infants' stool was collected pre-vaccination and at periods up to 6 months following COVID-19 vaccine series initiation/completion. SARS-CoV-2 antibody levels and their neutralization capacities were assessed.

RESULTS

SARS-CoV-2-specific IgA and IgG levels were higher in infant stool post-maternal vaccination amongst milk-fed compared to controls. Maternal SARS-CoV-2-specific IgA and IgG concentrations decreased over 6 months post-vaccination but remained higher than pre-vaccination levels. We observed improved neutralization capacity in milk and plasma after COVID-19 vaccination.

CONCLUSIONS

The presence of SARS-CoV-2-specific antibodies in infant stool following maternal vaccination offers further evidence of the lasting transfer of these antibodies through breastfeeding.

Detection of SARS-CoV-2 IgA and IgG in human milk and breastfeeding infant stool 6 months after maternal COVID-19 vaccination

Objective Assess the presence, durability, and neutralization capacity of SARS-CoV-2-specific antibodies in breastfeeding infants' stools, mother's plasma, and human milk following maternal vaccination. Design Thirty-seven mothers and 25 infants were enrolled between December 2020 and November 2021 for this prospective observational study. Human milk, maternal plasma, and infants' stools were collected pre-vaccination and at periods up to 6 months following COVID-19 vaccine series initiation/completion. SARS-CoV-2 antibody levels and their neutralization capacities were assessed in collected samples. Results SARS-CoV-2-specific IgA and IgG levels were higher in infant stool post-maternal vaccination amongst milk-fed compared to pre-COVID controls. Human milk and plasma SARS-CoV-2-specific IgA and IgG concentrations decreased over 6 months post-vaccination but remained higher than pre-vaccination levels. We observed improved neutralization capacity in milk antibodies over time. Conclusions The presence of neutralizing SARS-CoV-2-specific antibodies in infant stool following maternal vaccination offers further evidence of the lasting transfer of these antibodies through breastfeeding and their protective effect.

Detection of SARS-CoV-2 specific antibodies in breastfeeding infant stool following mother’s COVID-19 vaccination

In December 2020, efficacious COVID-19 vaccines were approved for use and since, millions have been immunized against SARS-CoV-2, the virus responsible for COVID-19. It is known that administration of the COVID-19 vaccine leads to increased SARS-CoV-2 specific antibodies in plasma and human milk. While this increase has been studied, the durability, longevity, and efficacy of these antibodies remains unknown. Historically, human milk serves a vital role in providing protection and nutrients to infants, and with COVID-19 vaccines not approved for children under five, immunity and protection from vaccinated mothers is likely a crucial barrier for infant safety. This study aimed at determining how long these antibodies remain in plasma and milk after COVID-19 vaccination, how effective these antibodies are at neutralizing SARS-CoV-2, and if antibodies are detectable in breastfeeding infant stool after mother has been vaccinated. This study found that concentrations of SARS-CoV-2 specific IgA and IgG decrease over 6 months post vaccine, but remain higher than pre-vaccination levels in plasma and milk. Although post-neutralization efficacy decreased over a 6-month period in plasma, using a pseudo-type vaccine neutralization assay, neutralization efficacy in human milk became more robust over the same period. Notably, we found elevated levels of SARS-CoV-2 specific IgA and IgG and neutralization within the stool of breastfeeding infants, post COVID vaccination compared to pre-COVID stool. Although further studies will be needed to determine the full extent of this passive immunity, these studies implicate the maternal/infant transfer of neutralizing SARS-CoV-2 specific antibodies through human milk subsequent to vaccination.

Supported by Children's Miracle Network