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takyon writes:

A new study has found that the FluMist nasal delivery system is just as reliable as other forms of a vaccine:

It came as a surprise this June when the Centers for Disease Control and Prevention recommended against using the nasal flu vaccine for the 2016-2017 flu season, citing a lack of evidence that it works. Now, findings from a Canadian study [DOI: 10.7326/M16-0513] appear at first blush to contradict the research that led the Advisory Committee on Immunization Practices [ACIP] to recommend against that live attenuated vaccine.

But things aren't so simple. In fact, the conflicting evidence about the live nasal flu vaccine offers an excellent case study on how complex the task of analyzing flu vaccine data and making recommendations really is. "Sometimes the public wants a very simple message, and unfortunately life's not like that," Mark Loeb, the new study's lead author and director of the division of infectious diseases at McMaster University in Ontario, tells Shots. "Things change as the evidence grows and we understand more. Unfortunately, that's how science and clinical medicine work. The challenge is to be able to help the public understand the shades of gray here."

[...] CDC data consistently showed the live nasal vaccine to be very effective in children until 2013, when the vaccine went from including three strains (trivalent) to including four strains (quadrivalent). And therein lies the rub: The new Canadian study used the trivalent vaccine, while ACIP analyzed data using the quadrivalent vaccine, and among U.S. children. "Many of us felt very strongly that the LAIV [live attenuated influenza vaccine] was a better vaccine than the inactivated for children, and the data supported that," says Pedro Piedra, a professor of virology and microbiology at Baylor College of Medicine and one of the investigators involved in the nasal vaccine clinical trials in the late 1980s. "But something happened when it became a quadrivalent vaccine."

Previously: CDC Advisory Panel Recommends Against "FluMist" Nasal Spray Vaccine System

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