Milk antibody response after 3rd COVID-19 vaccine and SARS-CoV-2 infection and implications for infant protection

Abstract

Little is known about the persistence of human milk anti-SARS-CoV-2 antibodies after 2^nd and 3^rd vaccine doses and infection following 3^rd dose. In this study, human milk, saliva, and blood samples were collected from 33 lactating individuals before and after vaccination and infection. Antibody levels were measured using ELISA and symptoms were assessed using questionnaires. We found that after vaccination, milk anti-SARS-CoV-2 antibodies persisted for up to 8 months. In addition, distinct patterns of human milk IgA and IgG production and higher milk RBD-blocking activity was observed after infection compared to 3-dose vaccination. Infected mothers reported more symptoms than vaccinated mothers. We examined the persistence of milk antibodies in infant saliva after breastfeeding and found that IgA was more abundant compared to IgG. Our results emphasize the importance of improving the secretion of IgA antibodies to human milk after vaccination to improve the protection of breastfeeding infants.

Keywords: Health sciences; Immunology; Pediatrics; Virology.

Graphical abstract

Figure 1

COVIPAL (A) Study timeline. (B) Enrollment schema.

Figure 2

Symptomatology following mRNA vaccine doses Fisher’s Exact test for independent samples was perform to compare symptoms reported after 3^rd dose to those reported after 1^st and 2^nd dose in lactating individuals, as previously reported. Asterisks indicate symptoms significantly different between 2^nd and 3^rd dose (p value < 0.01). No significant differences were observed between 1^st and 3^rd dose. Bars represent value.

Figure 3

Longitudinal persistence of anti-SARS-CoV-2 milk antibodies after vaccination and differential milk IgA responses following SARS-CoV-2 infection compared to post-vaccination (A–D) Anti-Spike IgG (A) and IgA (B) were measured in human milk samples and anti-RBD IgA (C) and IgG (D) were measured in plasma samples by Luminex assay, at multiple time points as represented in the X axis. Samples collected (1) pre-vaccine (2) post-dose 2 (range 4.7 to 7 weeks following 2^nd dose; (3) pre-boost (prior to 3^rd dose, range 26–37 weeks following 2^nd dose); (4) post-dose 3 (range 4–10 weeks following 3^rd dose; (5) post-infection (range 2–7 weeks following infection accruing after 3-dose vaccination series), and (6) 5 months after post-dose 3 (range 18–21 weeks after 3^rd dose). Dotted lines indicate the lower cut-off (aforementioned 1 considered positive). Upper limit of detection was at a ratio of 8.5. Asterisks represent p values: ∗= p value < 0.05, ∗∗= p value < 0.01, ∗∗∗= <0.001, ∗∗∗∗= <0.0001 as determined by unpaired Mann-Whitney test. Bars represent mean.

Figure 4

Milk RBD-blocking activity increases after vaccination and infection Milk samples were analyzed for neutralization activity (RBD binding capacity) using ELISA assay. Asterisks represent p values: ∗= p value < 0.05 as determined by unpaired Mann-Whitney test. Bars represent mean.

Figure 5

Persistence of maternal milk-derived SARS-CoV-2 antibodies in infant saliva after breastfeeding Milk and saliva samples were collected from mother and infants that were vaccinated with 2 doses of mRNA-based vaccine. (A–D) Two-tailed Spearman correlation was used to correlate milk and maternal saliva anti-Spike IgA levels (A) and IgG (B). In addition, anti-Spike IgA levels (C) and IgG (D) infant saliva samples were measured at multiple time points, immediately after breastfeeding (0), 30 min (30 min) after feeding, 1 h after feeding (1 h) and before next feeding (2–3 h after feeding). Maternal saliva was collected at the same day for comparison. Dotted lines indicate the lower cut-off (aforementioned 1 considered positive). Lines represent mean.