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Flu vaccine generated with a novel platform, using animal cell culture rather than egg, appeared to have good protection for children, a clinical trial showed.

Among kids ages 2 and up, the IIV4c vaccine had 54.6% efficacy (95% CI 45.7-62.1) in preventing laboratory-confirmed influenza compared with a non-influenza vaccine as a stand-in for placebo (incidence 7.8% vs 16.2%).

Adverse events were similar between groups, and efficacy was similar across age groups and prior influenza vaccination status, reported Alexandre C. Fortanier, PhD, of Seqirus Clinical Development in Amsterdam, and colleagues

These findings extended the evidence for efficacy seen in a with the cell-culture-derived trivalent inactivated influenza vaccine in adults, they noted.

The cell-based IIV4c vaccine gained on October 15 for use down to age 6 months under the same Flucelvax Quadrivalent name as the conventional version using standard propagation technology.

The new propagation technique uses a Madin-Darby canine kidney cell line, which had been hoped to actually improve efficacy. "Egg-adaptive mutations in the globular head of the hemagglutinin protein in egg-based vaccine viruses may contribute to observed low vaccine effectiveness," the researchers noted. "Genetic changes can be avoided through the use of manufacturing platforms that do not rely on eggs."

Another advantage is that vaccine manufacturing platforms that don't rely on eggs offer a shorter response time when a new virus emerges, they added, as has been seen with the use of mRNA vaccines against SARS-CoV-2.

"However, although the trial design and choice of comparator enabled an estimate of absolute efficacy of IIV4c, the absence of an influenza vaccine as a comparator does not permit an estimate of relative vaccine efficacy," Fortanier's group wrote. "Recently published studies of the relative effectiveness of egg-derived and non-egg-derived vaccines on the basis of real-world evidence may address the need for comparative assessments of benefit between vaccine platforms. Such studies may help us understand to what extent newer technology offers more effective prevention."

The IIV4c trial included 4,514 children ages 2 to 17 years in eight countries who were randomly assigned to receive an intramuscular shot of IIV4c or the meningococcal ACWY vaccine across three flu seasons from 2017 through 2019. Children under 9 years of age who hadn't previously gotten a flu shot got a second dose on day 29 or placebo as assigned.

In a post-hoc analysis, efficacy was similar in 2- and 3-year-olds as in the entire trial population, which the researchers said was "an important finding given the substantial influenza burden in young children and given the absolute vaccine efficacy in randomized clinical trials that evaluated standard, egg-based quadrivalent influenza vaccines, which showed a vaccine efficacy of 50% and 51% among children."

The IIV4c vaccine covered the two influenza type A subtypes (H1N1 and H3N2) and two influenza type B lineages (Yamagata and Victoria) as recommended by the WHO for the studied influenza seasons. Efficacy against those subtypes was:

• 80.7% (95% CI 69.2-87.9) against influenza A/H1N1
• 42.1% (95% CI 20.3-57.9) against influenza A/H3N2
• 47.6% (95% CI 31.4-60.0) against influenza B

Efficacy was similar across all three studied seasons, as well as sex and race/ethnicity.

"Because circulating influenza types and subtypes varied over the seasons, without a single predominating subtype or strain, estimates of vaccine efficacy against each of the detected subtypes and types over the course of the trial were robust," Fortanier's group wrote.

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