Addressing anti-syncytin antibody levels, and fertility and breastfeeding concerns, following BNT162B2 COVID-19 mRNA vaccination

Abstract

Objective: To determine whether antibodies against the SARS-CoV-2 spike protein following BNT162B2 (Pfizer-BioNTech) COVID-19 mRNA vaccination cross-react with human syncytin-1 protein, and if BNT162B2 mRNA enters breast milk. Methods: In this observational cohort study of female front-line workers with no history of COVID-19 infection, we amplified BNT162B2 mRNA in plasma and breast milk and assayed anti-SARS-CoV-2 neutralising antibodies and anti-human syncytin-1 binding antibodies in plasma, at early (1-4 days) and late (4-7 weeks) time points following first-dose vaccination. Results: Fifteen consented participants (mean age 40.4 years, various ethnicities) who received at least one dose of BNT162B2, including five breast-feeding women and two women who were inadvertently vaccinated in early pregnancy, were recruited. BNT162B2 mRNA, detected by amplifying part of the spike-encoding region, was detected in plasma 1-4 days following the first dose (n=13), but not 4-5 weeks later (n=2), nor was the mRNA isolated from aqueous or lipid breast milk fractions collected 0-7 days post-vaccination (n=5). Vaccine recipients demonstrated strong SARS-CoV-2 neutralising activity by at least four weeks after the first dose (n=15), including the two pregnant women. None had placental anti-syncytin-1 binding antibodies at either time-point following vaccination. Conclusions: BNT162B2-vaccinated women did not transmit vaccine mRNA to breast milk, and did not produce a concurrent humoral response to syncytin-1, suggesting that cross-reactivity to syncytin-1 on the developing trophoblast, or other adverse effects in the breast-fed infant from vaccine mRNA ingestion, are unlikely.

No evidence of fetal defects or anti-syncytin-1 antibody induction following COVID-19 mRNA vaccination

“…Finally, using human data we demonstrated that circulating anti-syncytin-1 antibodies do not rise following COVID-19 mRNA vaccination with either mRNA-1273 or BNT162B2. These findings support the mounting evidence that a syncytin-1-based mechanism of infertility is not supported by scientific observations [19,21]. This study is limited as we only interrogated the presence of anti-syncytin-1 in a total of 51 subjects.…”

“…Furthermore, many women at this stage in the pandemic have conceived following both COVID-19 infection and COVID-19 vaccination, with no reports of reduced fertility. Despite the absence of supporting evidence [21,22], the link between the mRNA vaccines and infertility persists, undermining mass vaccination campaigns worldwide.…”

Neutralizing Activity and SARS-CoV-2 Vaccine mRNA Persistence in Serum and Breastmilk After BNT162b2 Vaccination in Lactating Women

“…We also report the detection of low quantities of intact BNT162b2 mRNA in the serum and breastmilk samples – in 71% and 13% of the mothers investigated respectively. Several recent reports have inconsistently documented the presence of vaccine mRNA in the serum and breastmilk of women after BTN162b2 vaccination ( 13 , 35 , 36 ). The presence of intact vaccine mRNA in both sample types in our study highlights the stability and persistence of the vaccine mRNA nanoparticle within the bloodstream which may lead to infrequent transfer into breastmilk.…”

COVID-19 mRNA Vaccination in Lactation: Assessment of adverse events and vaccine related antibodies in mother-infant dyads

“…It has recently been shown in a few studies that vaccine mRNA is not present in milk samples after vaccination (17,18), or is only detected in very low levels in some cases (19), providing reassurance that risks of exposure to the breastfed infant are minimal. This study adds to the evidence that vaccine components are minimally transferred to human milk.…”