# Transfer of breast milk IgA to infants after oral bivalent norovirus vaccination of post-partum women

## TL;DR

This study shows that vaccinating breastfeeding women can transfer norovirus antibodies to infants through breast milk, offering protection against the virus.

## Contribution

Demonstrates passive transfer of norovirus-specific IgA from vaccinated mothers to infants via breast milk.

## Key findings

- Vaccinated mothers showed significantly enriched norovirus-specific antibodies in breast milk and serum.
- Infant stool IgA levels increased post-vaccination and correlated with breast milk IgA.
- The vaccine was safe and well tolerated with no severe adverse events.

## Abstract

Norovirus can cause severe and potentially fatal gastroenteritis in infants. Mucosal vaccination of breastfeeding women may promote infant protection by enriching antibody responses in consumed breast milk. Here, we report a double-blind, placebo-controlled phase 1 trial in South Africa (SANCTR: DOH-27-072023-7893) to evaluate a single-dose oral bivalent vaccine against norovirus genotypes GI.1 and GII.4 in post-partum breastfeeding women. Safety and reactogenicity (primary outcome), breast milk and serum norovirus-specific antibodies (primary outcome), and passive transfer of antibodies to infants as measured in infant stool (exploratory outcome) were assessed. The vaccine was safe and well tolerated with similar reports of mild or moderate adverse events between placebo (n = 16) and vaccine groups (5 × 1010 or 1 × 1011 IU/genotype, n = 30/group). Functional norovirus-specific breast milk and serum antibodies were significantly enriched in vaccinated groups. Norovirus-specific IgA in infant stool increased post-vaccination and positively correlated with breast milk IgA, indicating passive transfer. Thus, oral vaccination of breastfeeding women generates robust mucosal and systemic functional maternal antibodies. Our study presents a promising vaccination strategy to provide mucosal anti-norovirus immunity to infants.