Enhanced Influenza Vaccines May Benefit Older Adults in Mismatched Flu Seasons

Enhanced influenza vaccines may benefit adults age 65 and older in influenza seasons where the vaccine and circulating virus strains are mismatched, according to review findings published in Influenza and Other Respiratory Viruses.

Researchers sought to assess the immunogenicity of enhanced influenza vaccines against mismatched influenza strains in older adults. The investigators conducted a

literature search in PubMed Central, searching for RCTs that reported immunogenicity data for enhanced vaccines tested against heterologous, drifted, or mismatched influenza strains in a population aged 65 years and older. The search was conducted on May 31, 2023, for relevant articles published from 2014 to the present.

A total of 10 studies with immunogenicity data and 1 meta-analysis were identified for analysis.

The immunogenicity of the MF59-adjuvanted trivalent influenza vaccine (aIIV3) against heterologous strains, primarily A(H3N2) variants, was investigated in 10 studies. Of the studies, 1 compared aIIV3 with nonadjuvanted HD-IIV3 and RIV4, and 1 compared HD-IIV3 with standard-dose, nonadjuvanted IIV3.

Regarding adjuvanted influenza vaccines, aIIV3 was associated with more robust immune responses vs nonadjuvanted vaccines in most comparisons. In 1 study that compared aIIV3 with a nonadjuvanted, standard-dose trivalent subunit influenza vaccine, geometric mean titers (GMTs) against the 3 influenza vaccine antigens from A(H1N1), A(H3N2), and B strains were significantly increased in patients vaccinated with aIIV3 vs IIV3, with the greatest differences occurring in those with low pre-existing immunity, based on hemagglutination inhibition (HI) 28 days after vaccination.

Other research found that patients who were vaccinated with aIIV3 showed significantly higher postvaccination antibody responses than IIV3 recipients to 4 of 6 homologous and 8 of 9 drifted strains, including the drifted A/Brisbane/10/07-like and A/ Nepal/921/06-like strains, measured with HI or neutralizing GMT ratios.

In research conducted during the 2010 to 2011 season, the immunogenicity of aIIV3 compared with a subunit IIV3 was assessed, and postvaccination HI antibody responses were significantly increased for aIIV3 vs IIV3 against all homologous strains, especially A(H3N2), and against 2 heterologous A(H3N2) strains.

Immunogenicity of HD-IIV3 against a mismatched strain has been assessed in 1 study, and HD-IIV3 vs IIV3 induced significantly increased HI titers against the vaccine and circulating A/Victoria strains.

Heterologous immune responses among enhanced vaccines were evaluated in 1 study, which compared a quadrivalent recombinant vaccine with trivalent vaccines. During the 2017 to 2018 influenza season, microneutralization (MN) seroconversion rates against a heterologous virus were greater with RIV4 compared with aIIV3 or HDIIV3, with no significant differences in MN GMTs for that strain or in any measure for the homologous strains.

Among several limitations, only published trials in the US National Library of Medicine database were included, and few trials were available for HD-IIV and RIV4. In addition, the trials differed in demographic characteristics and the years that they were conducted.

“Compared with nonadjuvanted, standard-dose influenza vaccines, both adjuvanted and high-dose influenza vaccines elicited significantly higher antibody titers in separate studies,” the investigators stated.

Disclosure: This study was funded by CSL Seqirus Ltd. Some of the study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

This article originally appeared on Pulmonology Advisor