What is attenuated flu vaccine?

An attenuated flu vaccine is a type of influenza vaccine that uses weakened (attenuated) live virus to induce an immune response. When administered, the attenuated virus replicates within the body's cells but is unable to cause severe disease. This allows the immune system to develop antibodies that recognize and fight off the influenza virus without causing actual influenza symptoms.

Attenuated flu vaccines are made by growing a specific strain of the influenza virus in a controlled environment and then attenuating its virulence through laboratory means. Attenuation processes may involve repeated passages of the virus through animal or cell cultures over multiple generations, gradually reducing its ability to cause disease. This process ensures that the vaccine strain retains the characteristics necessary for triggering an effective immune response while minimizing the risk of causing severe illness.

Attenuated flu vaccines are typically administered intranasally (via the nose) and replicate within the respiratory tract, mimicking natural influenza infection. They provide broader immunity than inactivated flu vaccines as they induce both systemic and local immune responses, including the production of secretory antibodies (IgA) in the respiratory tract.

Attenuated flu vaccines can provide longer-lasting immunity compared to inactivated vaccines, and can also induce a protective response against drift variants (minor changes in the virus) of the vaccine strain. However, due to the use of live virus, attenuated vaccines may be contraindicated for certain individuals, such as those with weakened immune systems or certain health conditions.

Examples of attenuated flu vaccines include FluMist Quadrivalent (live attenuated influenza vaccine) and FluMist (live attenuated influenza vaccine seasonal).