Neutralizing antibodies in milk and blood of lactating women vaccinated for SARS-CoV-2: a systematic review.

Objective: To compare the presence of neutralizing antibodies against SARS-CoV-2 found in the breast milk and blood of vaccinated lactating women with those not vaccinated.

Data source: The study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) under CRD42021287554 and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Cohort, case-control, and cross-sectional studies that evaluated antibodies against SARS-CoV-2 in the milk and blood of vaccinated mothers and had as control group unvaccinated mothers were eligible. Health Sciences Descriptors (DeCs), Medical Subject Headings (MeSH) and Emtree descriptors were used for the Virtual Health Library (VHL), Medical Literature Analysis and Retrieval System Online (Medline/Pubmed), and Embase databases, respectively. In the Web of Science and Scopus, the strategy was adapted. No restrictions on the publication period and language were set.

Data synthesis: The search identified 233 records, of which 128 duplicates and 101 papers that did not meet the inclusion criteria were excluded. Hence, four cohort studies were eligible. Nursing mothers vaccinated with the Pfizer-BioNTech and Moderna vaccines showed antibodies against SARS-CoV-2 in their blood and breast milk.

Conclusions: Vaccinated lactating women had higher levels of immunoglobulin G (IgG) and A (IgA) in serum and breast milk than unvaccinated women.