Safety and Immunogenicity of Cell Culture-Derived A/H3N2 Variant Influenza Vaccines: A Phase I Randomized, Observer-Blind, Dose-Ranging Study

Analyses of Safety Profile and Homologous Antibody Responses to a Mammalian Cell-Based, MF59-Adjuvanted, A/H5N1, Pandemic Influenza Vaccine across Four Phase II/III Clinical Trials in Healthy Children, Adults, and Older Adults

Modern cell culture-based technology eliminates vaccine manufactures reliance on embryonated chicken eggs, which may become compromised during an avian influenza pandemic. Four studies (total N = 6230) assessed the immunogenicity and safety of mammalian cell-based, MF59^®-adjuvanted, A/H5N1 vaccine (aH5N1c; AUDENZ™) as two doses administered on Days 1 and 22 in children (NCT01776554), adults (NCT01776541; NCT02839330), and older adults (NCT01766921; NCT02839330). Immunogenicity of formulations at 7.5 μg and 3.75 μg antigen per dose were assessed by hemagglutination inhibition and microneutralization assays on Days 1, 22, 43, and 183 or 387. Solicited local and systemic adverse events (AEs) were recorded for 7 days after each vaccination. Unsolicited AEs were collected for 21 days after each vaccination, and serious and other selected AEs were recorded for one year. Antibody responses after two 7.5 μg doses met CBER licensure criteria in all age groups. Overall, an age-related response was evident, with the highest responses observed in children <3 years old. In children, antibody titers met seroconversion criteria 12 months after vaccination. MF59 allowed for antigen dose sparing. Solicited AEs were mild to moderate in nature, of short duration, and less frequent after the second dose than the first, demonstrating a favorable risk-benefit profile.

Establishment of a mouse- and egg-adapted strain for the evaluation of vaccine potency against H3N2 variant influenza virus in mice

Sporadic spreads of swine-origin influenza H3N2 variant (H3N2v) viruses were reported in humans, resulting in 437 human infections between 2011 and 2021 in the USA. Thus, an effective vaccine is needed to better control a potential pandemic for these antigenically distinct viruses from seasonal influenza. In this study, a candidate vaccine strain with efficient growth capacity in chicken embryos was established through serial blind passaging of A/Indiana/08/2011 (H3N2)v in mice and chicken embryos. Seven amino acid substitutions (M21I in PA; A138T, N165K, and V226A in HA; S312L in NP; T167I in M1; G62A in NS1 proteins) were found in the passaged viruses without a major change in the antigenicity. This mouse- and egg-adapted virus was used as a vaccine and challenge strain in mice to evaluate the efficacy of the H3N2v vaccine in different doses. Antibodies with high neutralizing titers were induced in mice immunized with 100 µg of inactivated whole-virus particles, and those mice were significantly protected from the challenge of homologous strain. The findings indicated that the established strain in the study was useful for vaccine study in mouse models.

Heterologous Antibody Responses Conferred by A(H3N2) Variant and Seasonal Influenza Vaccination Against Newly Emerged 2016-2018 A(H3N2) Variant Viruses in Healthy Persons

BACKGROUND

Swine origin A(H3N2) variant [A(H3N2)v] viruses continue to evolve and remain a public health threat. Recent outbreaks in humans in 2016-2018 were caused by a newly emerged A(H3N2)v cluster 2010.1, which are genetically and antigenically distinct from the previously predominant cluster IV. To address the public health risk, we evaluated the levels of heterologous cross-reactive antibodies to A(H3N2)v cluster 2010.1 viruses induced from an existing cluster IV A(H3N2)v vaccine and several seasonal inactivated influenza vaccines (IIVs) in adults, elderly individuals, and children.

METHODS

Human vaccine sera and ferret antisera were analyzed by hemagglutination inhibition (HI) and neutralization assays against representative A(H3N2)v viruses from clusters IV and 2010.1 and seasonal A(H3N2) viruses.

RESULTS

Ferret antisera detected no or little cross-reactivity between the 2 A(H3N2)v clusters or between A(H3N2)v and seasonal A(H3N2) viruses. In humans, cluster IV A(H3N2)v vaccine induced antibodies cross-reactive to cluster 2010.1 viruses in approximately one-third of the 89 adult and elderly vaccinees. Seasonal IIVs did not induce seroprotective antibodies (≥40) to A(H3N2)v viruses in young children, but induced higher antibodies to A(H3N2)v viruses in cluster 2010.1 than those in cluster IV in adults.

CONCLUSIONS

Cluster IV A(H3N2)v vaccine did not provide sufficient heterologous antibody responses against the new 2010.1 cluster A(H3N2)v viruses. Seasonal IIV could not induce seroprotective antibodies to 2010.1 cluster A(H3N2)v viruses in young children, suggesting that young children are still at high risk to the newly emerged A(H3N2)v viruses. Continued surveillance on A(H3N2)v viruses is critical for risk assessment and pandemic preparedness.

Safety and Immunogenicity of MF59-Adjuvanted Cell Culture-Derived A/H5N1 Subunit Influenza Virus Vaccine: Dose-Finding Clinical Trials in Adults and the Elderly

Background

A/H5N1 influenza viruses have high pandemic potential; consequently, vaccines need to be produced rapidly. MF59® adjuvant reduces the antigen required per dose, allowing for dose sparing and more rapid vaccine availability.

Methods

Two multicenter, phase II trials were conducted to evaluate the safety and immunogenicity of an MF59-adjuvanted, cell culture–derived, A/H5N1 vaccine (aH5N1c) among 979 adult (18–64 years old) and 1393 elderly (≥65 years old) subjects. Participants were equally randomized to receive 2 full-dose (7.5 μg of hemagglutinin antigen per dose) or 2 half-dose aH5N1c vaccinations 3 weeks apart. Outcomes were based on Center for Biologics Evaluation Research and Review (CBER) and Committee for Medicinal Products for Human Use (CHMP) licensure criteria (titers ≥1:40 and seroconversions on day 43). Solicited reactions and adverse events were assessed (www.clinicaltrials.gov: NCT01776541 and NCT01766921).

Results

CBER and CHMP criteria were met by both age groups. CBER criteria for hemagglutination titers were met for the full-dose formulation. Solicited reaction frequencies tended to be higher in the full-dose group and were of mild to moderate intensity. No vaccine-related serious adverse events occurred.

Conclusions

In adult and elderly participants, the full-dose aH5N1c vaccine formulation was well tolerated and met US and European licensure criteria for pandemic vaccines.

Amino Acids in Hemagglutinin Antigenic Site B Determine Antigenic and Receptor Binding Differences between A(H3N2)v and Ancestral Seasonal H3N2 Influenza Viruses

Influenza A H3N2 variant [A(H3N2)v] viruses, which have caused human infections in the United States in recent years, originated from human seasonal H3N2 viruses that were introduced into North American swine in the mid-1990s, but they are antigenically distinct from both the ancestral and current circulating H3N2 strains. A reference A(H3N2)v virus, A/Minnesota/11/2010 (MN/10), and a seasonal H3N2 strain, A/Beijing/32/1992 (BJ/92), were chosen to determine the molecular basis for the antigenic difference between A(H3N2)v and the ancestral viruses. Viruses containing wild-type and mutant MN/10 or BJ/92 hemagglutinins (HAs) were constructed and probed for reactivity with ferret antisera against MN/10 and BJ/92 in hemagglutination inhibition assays. Among the amino acids that differ between the MN/10 and BJ/92 HAs, those in antigenic site A had little impact on the antigenic phenotype. Within antigenic site B, mutations at residues 156, 158, 189, and 193 of MN/10 HA to those in BJ/92 switched the MN/10 antigenic phenotype to that of BJ/92. Mutations at residues 156, 157, 158, 189, and 193 of BJ/92 HA to amino acids present in MN/10 were necessary for BJ/92 to become antigenically similar to MN/10. The HA amino acid substitutions responsible for switching the antigenic phenotype also impacted HA binding to sialyl receptors that are usually present in the human respiratory tract. Our study demonstrates that antigenic site B residues play a critical role in determining both the unique antigenic phenotype and receptor specificity of A(H3N2)v viruses, a finding that may facilitate future surveillance and risk assessment of novel influenza viruses.

IMPORTANCE

Influenza A H3N2 variant [A(H3N2)v] viruses have caused hundreds of human infections in multiple states in the United States since 2009. Most cases have been children who had contact with swine in agricultural fairs. These viruses originated from human seasonal H3N2 viruses that were introduced into the U.S. swine population in the mid-1990s, but they are different from both these ancestral viruses and current circulating human seasonal H3N2 strains in terms of their antigenic characteristics as measured by hemagglutination inhibition (HI) assay. In this study, we identified amino acids in antigenic site B of the surface glycoprotein hemagglutinin (HA) that explain the antigenic difference between A(H3N2)v and the ancestral H3N2 strains. These amino acid mutations also alter binding to minor human-type glycans, suggesting that host adaptation may contribute to the selection of antigenically distinct H3N2 variants which pose a threat to public health.