The spring arrivals are growing up and the question of when to vaccinate is creeping up.  If vaccinated too early, the vaccine is virtually wasted since the baby received protection against disease in his mother’s milk (called maternal antibodies).  If administered too late, the foal is left vulnerable to infection because the maternal antibodies are no longer at protective levels.  Unfortunately, the rate at which these antibodies decline varies for each individual, but there are ways in which your veterinarian can help estimate when your foal will need active (a.k.a. vaccine induced) immunity. Concentrations of maternal antibody in the average foal drop to non-protective levels by two to three month of age.  However, many of these will not respond to vaccinations for weeks or even months.  Therefore, equine practitioners recommend postponing most vaccinations until three or four months of age.           
While for most foals vaccinating at three or four months is adequate, a significant number of foals are in “high risk” situations.  This may include boarding stables, horse shows, or other situations which expose them to other horses of unknown vaccination and disease history.  In these instances it is important to adjust the vaccination regime to meet the needs of the individual foal.  The following table contains the general recommendations of the American Association of Equine Practitioners for foal vaccinations*. 

*  Additional vaccinations may include PHF, rabies, botulism, and STRANGLES which are used in endemic areas or where the risk is high.  VEE is used in Texas or where the threat of an outbreak exists. **  The ‘Yearling Regime’  for  EEE/WEE/Tetanus is an annual spring booster.  For influenza and rhino it is every 3 to 6 months, depending on the risk of infection and vaccination status of the dam.  

Links for more information

 AAEP Online