**Core Concept**
Live attenuated vaccines are administered via intranasal or intramuscular routes depending on the vaccine type. In the case of influenza, the H1N1 live vaccine is specifically designed as a live attenuated vaccine, which stimulates strong mucosal and systemic immunity by replicating in the respiratory tract.

**Why the Correct Answer is Right**
The H1N1 live vaccine (e.g., the seasonal trivalent or quadrivalent influenza vaccine containing live attenuated strains) is administered intranasally to mimic natural infection. This route allows the virus to replicate in the upper respiratory tract, inducing local IgA and T-cell responses. Live attenuated vaccines like H1N1 live are preferred for their robust immune response and longer protection, especially in children and high-risk populations.

**Why Each Wrong Option is Incorrect**
Option A: Typhoral live (likely a typo for typhoid live) is administered orally, not via intranasal route. It is a live vaccine but not for H1N1.
Option B: H1N1 killed vaccine is given intramuscularly and is not live. It lacks mucosal immunity and is less effective in inducing local defense.
Option D: Yellow fever live vaccine is given intramuscularly and is not used for influenza. It is a live vaccine but for yellow fever, not H1N1.

**Clinical Pearl / High-Yield Fact**
Live attenuated vaccines (like H1N1 live) are given **intranasally** to induce **mucosal immunity**, while inactivated vaccines (like killed H1N1) are given **intramuscularly**. Always remember: **"Live = nasal, Killed = IM"** for influenza.

✓ Correct Answer: C. H1N1 live