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SAN FRANCISCO -- Cell culture-based inactivated influenza vaccine (IIV) was not significantly more effective than egg-based IIV against influenza A during the 2017-2018 flu season, a researcher said here.

The relative vaccine effectiveness of cell culture-based IIV versus egg-based IIV against influenza A was 8% (HR 0.92, 95% CI -10% to 23%, P=0.36), but the difference between the two was non-significant, Nicola Klein, MD, of Kaiser Permanente in Oakland, California, reported.

The study was a at IDWeek, with joint sponsorship by the (IDSA), the (PIDS), the (SHEA), and the (HIVMA).

Klein said that reports from the CDC indicated that vaccine effectiveness (VE) against the predominant strain in the 2017-2018 season, influenza A (H3N2), was around 24% on average. She added that "this lower-than-expected VE was hypothesized to be partially related to genetic changes arising in the vaccine during passage in eggs," and that this "raises the question of whether cell-culture based inactivated influenza vaccines are more effective."

, William Schaffner, MD, professor of preventive medicine and infectious diseases at Vanderbilt University in Nashville, spoke in general about upcoming advances in flu vaccines -- characterizing the current flu vaccine as "good, but not great." Schaffner touched on the hope surrounding new technologies, such as cell-based vaccines.

"[These] vaccines are going to be created, not in the ancient way of manufacturing them in eggs, but in other modalities. It's really kind of remarkable -- that might get us better antigens," he told MedPage Today. "Anything we can do to improve the quality of the vaccine I think will lead to ... more enthusiasm on the part of the provider to actually get everybody vaccinated."

Klein and colleagues examined the effectiveness of the currently available cell culture-based IIV Flucelvax (manufactured by Seqirus) as compared with an egg-based IIV among members of Kaiser Permanente Northern California (KPNC), ages 4-64 years. Members were followed through the end of the the 2017-2018 influenza season, disenrollment from KPNC or death. A positive influenza PCR test was defined as influenza positive.

They compared both vaccines in a head-to-head comparison (relative vaccine effectiveness), as well as each vaccine separately with unvaccinated individuals (absolute vaccine effectiveness).

Overall, there were over 3 million total people, ages 4-64, in the study, with about 1 million vaccinated. Of those vaccinated, about 8.3% received cell culture-based IIV.

Moreover, there were about 5,800 who were influenza A-positive and about 70% of those were unvaccinated. About a quarter received egg-based vaccine and 2.4% received cell culture-based vaccine.

While there was no significant difference between vaccine types, when compared with unvaccinated persons, absolute vaccine effectiveness of cell culture-based vaccine (31.7%, 95% CI 18.7%-42.6%, P<0.0001) and egg-based IIV (20.1%, 95% CI 14.5%-25.4%, P<0.0001) was significantly higher for both for influenza A.

Angela Branche, MD, of the University of Rochester Medical Center in New York, who was not involved in the study, cited the absolute effectiveness as opposed to the relative effectiveness of the vaccines when comparing the two, saying that the poor effectiveness of both may have been partially related to strain mismatch.

“When the absolute vaccine effectiveness is taken into consideration, Flucelvax performed better than the egg-based vaccine despite the fact that the numbers of vaccines for the cell-based group was relatively small compared to the egg-based vaccine group,” Branche told MedPage Today, adding that this research suggests that “Flucelvax may be a better vaccination strategy going forward and should be adopted into clinical practice more widely.”

Researchers also compared both relative and absolute vaccine effectiveness against influenza B. While relative vaccine effectiveness of the cell-culture based vaccine was 39.6% (95% CI 27.9%-49.3%, P<0.0001), this was compared with the egg-based trivalent vaccine, which contained B virus of Victoria lineage.

Absolute vaccine effectiveness was 40.9% versus unvaccinated people for cell-cultured based vaccine (95% CI 30.0%-50.1%, P<0.0001), but 9.7% for the egg-based trivalent vaccine (95% CI 3.5%-15.6%, P=0.0028).

However, Klein said that 83% of B viruses in Northern California were Yamagata strain, so these numbers were "about what we'd expect, given what circulated in the season."

She concluded that the data hinted that cell culture-based vaccine was "moderately more effective" against influenza A than egg-based vaccines, but the difference was non-significant, and that this vaccine provided "good effectiveness" against influenza B.

"Ongoing monitoring of vaccine effectiveness is crucial, but most of all, we need better vaccines," Klein said.

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