The mechanism of protection in the FluMist

In a new research published in this month’s issue of Vaccine, scientist and author Dr. Laura Haynes and team from the Trudeau Institute shed new light on why the FluMist, or live attenuated influenza vaccine (LAIV), triggers protection.
Dr. Laura Haynes said, “Our research specifically examines how the vaccine, which is commonly known as FluMist, elicits protection. Influenza infection normally induces a massive inflammatory response in the lungs that leads to significant illness and increases the susceptibility to secondary bacterial infections.”

She added, “The most efficient way to prevent influenza infection is through vaccination. To date, the mechanism of how FluMist induces protection has been unclear. Our study demonstrates that this vaccine works by inducing a very early non-specific immune response in the lungs in a mouse model of influenza infection.”

Viral clearance occurs due to an early non-specific immune response that facilitates early entry of virus-specific immune cells. Both matching and non-matching influenza strains are affected by this protective immune response, which renders such an immune response that can take on even a newly emergent influenza strain.

Furthermore, the levels of inflammatory cytokines and chemokines produced because of influenza infection can be significantly reduced by this early-stage immune response that prevents lung inflammation.

Inflammation is a main cause of lung damage, and this can facilitate secondary bacterial infections, a common feature after influenza infection. This novel discovery is vital because it furthers the understanding of the functioning of the influenza vaccine.

In healthy adult volunteers, the LAIV vaccine has been found to induce a robust immune response, according to the study findings.

The commercially available FluMist vaccine was administered to participants enrolled by the Naval Health Research Center (NHRC). An evaluation of the immune response to the vaccine at precise time points following vaccination revealed that chemokines and cytokines involved in virus-specific lymphocyte recruitment were produced.

This pinpoints to a protective immune response that would allow early recruitment of immune cells to the lung in cases of reoccurrence of influenza infection. Early arrival of immune cells to the lung is extremely advantageous as it facilitates rapid viral clearance and decreases inflammation levels.

These translational experiments were carried out at the NHRC in San Diego, CA in partnership with the Respiratory Diseases Research Department and were the result of a joint Trudeau/Department of Defense contract. The research is supported by government grants and philanthropic contributions. The journal article is entitled “Live attenuated influenza vaccine (LAIV) impacts innate and adaptive immune responses.”

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