- The Influenza vaccine (nasal spray) is the only option administered as a live-attenuated vaccine via the nasal route.
- This formulation uses a weakened but viable virus to stimulate local mucosal immunity in the respiratory tract.
- In contrast, MMR is given via injection, IPV is an inactivated injectable vaccine, and Hepatitis B vaccine is also injectable and inactivated.
- The live-attenuated nasal spray allows for a more natural immune response by mimicking the natural route of infection.

Reference: Principles of Infectious Diseases, Volume 1, Chapter 45