Vaccines (ATCvet codes: inactivated, live, plus various combinations) are a major defense against the disease. Vaccination schedules generally require a primary course of vaccines, followed by booster shots. It is recommended that horses be vaccinated against equine influenza annually, and competition horses that travel frequently be given a booster every six months as they are at higher risk of contracting the virus. Foals are initially vaccinated at six months of age with a booster 3 to 6 weeks later and again between 10 and 12 months. Standard schedules may not maintain absolutely foolproof levels of protection, and more frequent administration is advised in high-risk situations.