Maternal antibodies against equine influenza virus in foals and their interference with vaccination.

This study investigates the impact of maternal antibodies against the equine influenza virus on foals’ response to vaccination, finding that maternal antibodies may hinder vaccine-induced antibody production. It suggests delaying foal vaccination until maternal antibodies have decreased to an inconsequential level.

Research Method and Approach

• The study focused on foals born to mares that had been vaccinated twice a year against influenza.
• After birth, these foals showed moderate to high levels of haemagglutination-inhibition antibody titers (a type of test to measure the levels of antibodies in the blood).
• To evaluate the vaccines’ effectiveness, these foals were then vaccinated at intervals: at six and ten weeks of age and again three to five months after birth.

Findings and Observations

• Four months after the third vaccination, these foals showed no antibodies against two strains of equine influenza virus (A/H7N7 and A/H3N8). This indicates that the maternal antibodies likely hindered the development of the foals’ own antibodies against the virus.
• To further investigate this effect, foals born to the same mares a year later were examined to determine the duration and decline rate of these maternal antibodies.
• The foals’ antibody levels shortly after their birth matched those of their mothers at foaling, showing that the mother’s immunization program significantly influenced the foals’ immunity.
• These antibodies persisted in the foals for three to six months and had an estimated biological half-life of about 38 days.

Recommendations and Implications

• Two vaccinations against influenza were given to the foals after these maternal antibodies had nearly disappeared, resulting in an antibody response in most, though not all, foals. This suggests the presence of maternal antibodies may lower the effectiveness of the vaccination.
• The findings highlight the possibility of delaying vaccination until most maternal antibodies have disappeared. This can potentially improve the success rate of the vaccination process and protect the young foals more effectively against equine influenza virus.