# Long‐Term Maintenance of High Neutralizing Anti‐SARS‐CoV‐2 Antibodies Titres in Mares’ Milk and Offspring Serum After Pregnant Mares Immunization With SARS‐CoV‐2 Spike Protein

## TL;DR

Pregnant mares immunized with SARS-CoV-2 spike protein passed high levels of neutralizing antibodies to their foals through milk, which lasted for six weeks.

## Contribution

Demonstrates a novel method to track antibodies from vaccinated pregnant mares to their offspring through milk and serum.

## Key findings

- High and persistent IgG and neutralizing antibodies were found in mares' serum, colostrum/milk, and foal serum.
- Antibodies remained elevated for six weeks post-parturition in both mares and their offspring.
- The study used a unique approach to track antibodies from antigen-inoculated pregnant mares to their offspring.

## Abstract

In this study, we aim to report the persistent presence of anti‐SARS‐CoV‐2 immunoglobulins in pre‐immunized mare offspring. Three mares from Vital Brazil Institute were pre‐immunized with recombinant SARS‐CoV‐2 spike protein and became pregnant during this period. After parturition, the mares’ serum and colostrum/milk and foal serum were collected over 6 weeks. Our results have shown high and persistent presence of IgG and neutralizing antibodies over the weeks not only in the mares’ serum, as expected, but in mares’ colostrum/milk and foal serum as well—what were very surprising. This peculiar approach, which we were able to track specifically antibodies produced from an antigen inoculated only in the pregnant mares’, is distinct from the usual methodology applied in the current reports in this field. Thus, together, these data and our methodology could lead to new approaches to better understanding about equine passive immunization by newborn's breast‐feeding.

This study investigated the total and neutralizing antibodies transferred to offspring from three mares from Vital Brazil Institute that were pre‐immunized with recombinant SARS‐CoV‐2 trimeric spike protein. They became pregnant during the immunization protocol. After parturition, the mare's serum and colostrum and foal serum showed high total and neutralizing antibodies against SARS‐CoV‐2 over 6 weeks.