Vaccines are biological preparations that stimulate the immune system to develop protection against specific diseases. Immunization programs have eliminated or greatly reduced many once-devastating diseases including smallpox, polio, measles, and diphtheria. Vaccines work by introducing weakened, killed, or partial pathogens (or their genetic instructions), triggering immune responses without causing disease. Provincial health programs provide routine childhood immunizations and adult vaccines according to national immunization schedules. School immunization requirements vary by province. Public health programs promote vaccination through education, accessible clinics, and sometimes mandates. Vaccine hesitancy presents public health challenges, requiring communication about vaccine safety and effectiveness. Recent mRNA technology enabled rapid COVID-19 vaccine development, demonstrating continued vaccine innovation.