Seqirus already has the first and only FDA-approved cell-based flu vaccine, Flucelvax, for people four years and older. Now, aiming for a younger population, the CSL subsidiary has returned with phase 3 data showing an adjuvanted quadrivalent flu shot could be a better choice than non-adjuvanted options.

In a recent phase 3 study, Seqirus’ MF59-adjuvanted quadrivalent flu vaccine (aQIV) provided 31% more protection than another FDA-approved non-adjuvanted comparator in those younger than two years old. The boost in protection—as measured by RT-PCR confirmed, culture-confirmed and antigenically matched influenza—wasn't seen in all age groups across the study population.

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The head-to-head study, which spanned the 2013-14 and 2014-15 flu seasons, vaccinated 10,612 children aged 6 months to 5 years with one or two doses of either aQIV or the comparator. The company didn't disclose the comparator shot. The Seqirus shot, when given at two dosages to kids who have never been vaccinated against influenza, turned out to be even more effective than the comparator in preventing influenza before the second dose.

The CDC currently recommends that vaccine-naïve children 6 months through 8 years get two doses of a flu vaccine instead of the usual one dose. Lead researcher of the study, Timo Vesikari, M.D., Ph.D., with the University of Tampere Medical School, said the result could mean that aQIV improves protection even after a single dose.

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"Our study demonstrated that aQIV represents an important new opportunity to introduce a potentially improved influenza vaccine option," Vesikari said in a statement.

Two companies currently market quadrivalent flu shots in the U.S. for kids starting from 6 months old: Sanofi Pasteur markets Fluzone Quadrivalent, and GlaxoSmithKline is selling Flulaval Quadrivalent. Besides Flucelvax Quadrivalent for those 4 years and older, Seqirus also has Afluria Quadrivalent approved for use in adults and several trivalent flu vaccines for different age groups.