What's new in flu: FluMist vaccine elicits immune response before influenza

Flumist flu vaccine
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In a joint research study by scientists at the Trudeau Institute and the Department of Defense (DOD), new findings demonstrate why the attenuated flu vaccine known as FluMist works so well in combatting influenza. Prior to their findings, the mechanism of protection was poorly understood. Today, scientists now know that FluMist elicits a novel and adaptive immune response in the lungs that offers protection before infection.

Influenza infection and flu vaccine FluMist

An influenza infection is a serious medical condition that causes a massive inflammatory response in the cells of the lungs. The result of the inflammation is that it makes the lungs susceptible to secondary bacterial infections that can leave a person bedridden for weeks resulting in lung damage and sometimes death.

Prior to FluMist, flu vaccines consisted of an inactivated or killed virus delivered via a needle injection. The vaccine would then stimulate the body’s immune system to generate antibodies in the bloodstream that would protect the individual if exposed to a live flu virus afterward during the cold and flu season.

FluMist differs from the injectable flu vaccine in four ways: (1) The vaccine consists of a live (but weakened) flu virus designed not to cause an influenza infection. (2) The vaccine is delivered via a spray into each nostril. (3) The vaccine works by producing flu antibodies in the nose where flu infection begins. (4) The vaccine does not contain thimerosol or mercury, which typically are used as preservatives in injectable forms of vaccines.

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Using mouse models of influenza infection, the researchers found that the FluMist vaccine induces a very early, non-specific immune response in the lungs that paves the way for a virus-specific immune response afterward in the lungs. These responses are protective against both matching and non-matching flu strains, which may protect the lungs when a new viral strain emerges.

A second finding was that the FluMist vaccine also limits the levels of cytokines and chemokines that are released during flu-induced lung inflammation. Cytokines are chemical messengers that signal and stimulate cells of the immune system to produce chemicals needed to fight infection. Chemokines are chemical attractants that bring immune system cells such as leukocytes, monocytes and neutrophils to the sites of infection. While cytokines and chemokines play important roles in the immune response, levels that are too high are harmful.

Human Studies
Vaccinating healthy adult volunteers with commercially available FluMist resulted in findings that demonstrated an immune response of lymphocytes in their lungs that are virus-specific. This indicates that the lungs of the subjects are actually prepped ahead of time before exposure to a natural virus. In the event of an influenza infection, such an early response is expected to result in an early clearance of the virus from the lungs as well as reduced inflammation.

The results of this study are published in the August 2011 issue of Vaccine.

Resources: http://trudeauinstitute.org/dynamicPages/pressReleases.cfm?action=view&listingID=183&ID=100&navTable=tier2nav
Live attenuated influenza vaccine (LAIV) impacts innate and adaptive immune responses Paula A. Lanthier, Gail E. Huston, Amy Moquin, Sheri M. Eaton, Frank M. Szaba, Lawrence W. Kummer, Micheal P. Tighe, Jacob E. Kohlmeier, Patrick J. Blair, Michael Broderick, Stephen T. Smiley and Laura Haynes, doi:10.1016/j.vaccine.2011.07.093

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