Immunize/ˈɪmjunaɪz/ Definition 1 of 2Pro Tip 1/3Disease Prevention Immunize is used when someone receives a vaccine to prevent diseases. Travelers are advised to immunize before visiting certain regions. Pro Tip 2/3Medical Context Most common in medical and health-related conversations or articles. Please ensure you immunize your pets against rabies. Pro Tip 3/3Preventive Action Implies action taken before exposure to disease, not after. Countries immunize populations to prevent epidemic outbreaks.