The Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee has chosen the influenza vaccine strains for the 2022-2023 season in the northern hemisphere, which begins in the fall of 2022.
On March 3, the committee unanimously voted to endorse the World Health Organization’s recommendations as to which influenza strains to include for coverage by vaccines for the upcoming flu season. Two of the four recommended strains are different from last season.
The committee also heard updates on flu activity this season. So far, data from the U.S. Flu Vaccine Effectiveness (VE) network, which consists of seven study sites, have not shown that the vaccine is protective against influenza A. “We can say that it is not highly effective,” Brendan Flannery, PhD, who leads the U.S. Flu VE network for the Centers for Disease Control and Prevention, said in an interview. He was not involved with the advisory committee meeting. Flu activity this season has been low, he explained, so there are fewer cases his team can use to estimate vaccine efficacy. “If there’s some benefit, it’s hard for us to show that now,” he said.
The panel voted to include a A/Darwin/9/2021-like strain for the H3N2 component of the vaccine; this is changed from A/Cambodia/e0826360/2020. For the influenza B Victoria lineage component, the committee voted to include a B/Austria/1359417/2021-like virus, a swap from this year’s B/Washington/02/2019-like virus. These changes apply to the egg-based, cell-culture, and recombinant vaccines. Both new strains were included in WHO’s 2022 influenza vaccine strain recommendations for the southern hemisphere.
For the influenza A H1N1 component, the group also agreed to include a A/Victoria/2570/2019 (H1N1) pdm09-like virus for the egg-based vaccine and the A/Wisconsin/588/2019 (H1N1) pdm09-like virus for cell culture or recombinant vaccines. These strains were included for the 2021-2022 season. The panel also voted for the inclusion of a B/Phuket/3073/2013-like virus (B/Yamagata lineage) as the second influenza B strain for the quadrivalent egg-based, cell culture, or recombinant vaccines, which is unchanged from this flu season.
‘Sporadic’ flu activity
While there was an uptick in influenza activity this year compared to the 2020-2021 season, hospitalization rates are lower than in the four seasons preceding the pandemic (from 2016-2017 to 2019-2020). As of Feb. 26, the cumulative hospitalization rate for this flu season was 5.2 hospitalizations per 100,000 individuals. There have been eight pediatric deaths due to influenza so far this season, compared to one pediatric death reported to the CDC during the 2020-2021 flu season.
About 4.1% of specimens tested at clinical laboratories were positive for flu. Since Oct. 30, 2.7% of specimens have been positive for influenza this season. Nearly all viruses detected (97.7%) have been influenza A.
Lisa Grohskopf, MD, MPH, a medical officer in the influenza division at the CDC who presented the data at the meeting, described flu activity this season as “sporadic” and noted that activity is increasing in some areas of the country. According to CDC’s weekly influenza surveillance report, most states had minimal influenza-like illness (ILI) activity, although Arkansas, Idaho, Iowa, Kansas, Minnesota, and Utah had slightly higher ILI activity as of Feb. 26. Champaign-Urbana, Illinois; St. Cloud, Minnesota; and Brownwood, Texas, had the highest levels of flu activity in the country.