Safety, Tolerability and Immunogenicity of an MF59-adjuvanted, Cell Culture-derived, A/H5N1, Subunit Influenza Virus Vaccine: Results From a Dose-finding Clinical Trial in Healthy Pediatric Subjects

Pandemic preparedness through vaccine development for avian influenza viruses

Influenza A viruses pose a significant threat to global health, impacting both humans and animals. Zoonotic transmission, particularly from swine and avian species, is the primary source of human influenza outbreaks. Notably, avian influenza viruses of the H5N1, H7N9, and H9N2 subtypes are of pandemic concern through their global spread and sporadic human infections. Preventing and controlling these viruses is critical due to their high threat level. Vaccination remains the most effective strategy for influenza prevention and control in humans, despite varying vaccine efficacy across strains. This review focuses specifically on pandemic preparedness for avian influenza viruses. We delve into vaccines tested in animal models and summarize clinical trials conducted on H5N1, H7N9, and H9N2 vaccines in humans.

Phase 3 Randomized, Multicenter, Placebo-Controlled Study to Evaluate Safety, Immunogenicity, and Lot-to-Lot Consistency of an Adjuvanted Cell Culture-Derived, H5N1 Subunit Influenza Virus Vaccine in Healthy Adult Subjects

A cell-based process may be better suited for vaccine production during a highly pathogenic avian influenza (HPAI) pandemic. This was a phase 3, randomized, controlled, observer-blind, multicenter study evaluated safety, immunogenicity, and lot-to-lot consistency of two doses of a MF59-adjuvanted, H5N1 influenza pandemic vaccine manufactured on a cell culture platform (aH5N1c) in 3196 healthy adult subjects, stratified into two age groups: 18 to <65 and ≥65 years. Immunogenicity was measured using hemagglutination inhibition (HI) titers. HI antibody responses increased after the first aH5N1c vaccine dose, and 3 weeks after the second vaccination (Day 43), age-appropriate US Center for Biologics Evaluation and Research (CBER) and former European Medicines Authority Committee for Medicinal Products for Human Use (EMA CHMP) immunogenicity criteria were met. Six months after the first vaccination, HI titers were above baseline but no longer met CBER and CHMP criteria. No relevant changes over time were seen in placebo subjects. Solicited AEs were more frequent in the active treatment than the placebo group, primarily due to injection site pain. No serious adverse events (SAEs) related to aH5N1c- were reported. aH5N1c influenza vaccine elicited high levels of antibodies following two vaccinations administered 21 days apart and met both CBER and former CHMP immunogenicity criteria at Day 43 among both younger and older adults with a clinically acceptable safety profile. Consistency of the three consecutive aH5N1c vaccine lots was demonstrated (NCT02839330).

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.

Antibody responses against heterologous A/H5N1 strains for an MF59-adjuvanted cell culture-derived A/H5N1 (aH5N1c) influenza vaccine in healthy pediatric subjects

BACKGROUND

Vaccines are the main prophylactic measure against pandemic influenza. Adjuvanted, cell culture-derived vaccines, which are not subject to limitations of egg-based vaccine production, have the potential to elicit an antibody response against heterologous strains and may be beneficial in the event of an A/H5N1 pandemic.

METHODS

A prespecified exploratory analysis of data from a phase 2, randomized, controlled, observer-blind multicenter trial (NCT01776554) to evaluate the immunogenicity of a MF59-adjuvanted, cell culture-based A/H5N1 influenza vaccine (aH5N1c), containing 7.5 µg hemagglutinin antigen per dose, in subjects 6 months through 17 years of age was conducted. Geometric mean titers (GMT) were determined using hemagglutination inhibition (HI) and microneutralization (MN) assays, and proportions of patients achieving seroconversion, HI and MN titers ≥ 1:40, and a 4-fold increase in MN titers against 5 heterologous strains (influenza A/H5N1 Anhui/2005, Egypt/2010, Hubei/2010, Indonesia/2005, and Vietnam/1203/2004) three weeks after administration of the second dose were assessed.

RESULTS

After the second dose, HI GMTs against heterologous strains increased between 8- and 40-fold, and MN GMTs increased 13- to 160-fold on Day 43 vs Day 1. On Day 43, 32-72% of subjects had HI titers ≥ 1:40 and achieved seroconversion against the heterologous strains. Using the MN assay, 84-100% of subjects had MN titers ≥ 1:40 and 83-100% achieved an at least 4-fold increase in MN titers against the heterologous strains. The highest responses were consistently against A/H5N1 Egypt/2010.

CONCLUSIONS

When given to children aged 6 months through 17 years, aH5N1c resulted in increased immunogenicity from baseline against all 5 heterologous A/H5N1 strains tested, demonstrating the potential of an MF59-adjuvanted, cell-derived A/H5N1 vaccine to provide cross-protection against other A/H5N1 strains (NCT01776554).

Evaluation of safety and immunogenicity of feline vaccines with reduced volume

A non adjuvanted vaccine against feline herpesvirus, feline calicivirus, feline panleucopenia and feline leukemia has been formulated in reduced volume (0.5 ml) with the same antigen content as the conventional 1 ml presentation. This paper reports studies evaluating the safety and the immunogenicity of this reduced volume vaccine in comparison with the conventional volume vaccine. The safety of both vaccines was evaluated in a small sized laboratory trial. It was further tested in a randomized controlled field trial on a total of 398 cats. Immediate and delayed local and systemic adverse events were monitored after vaccination. The immunogenicity of each vaccine was also checked by serological antibody responses against the vaccines antigens during the laboratory trial. These studies showed that the 0.5 ml vaccine was well tolerated in cats, inducing less local events, while keeping the same immunogenicity as the corresponding 1 ml vaccine. Reducing the volume of the vaccine is a way to improve the convenience of administration and to help following vaccination guidelines with the aim of reducing the incidence of adverse events following vaccination.

The continued advance of vaccine adjuvants - 'we can work it out'

In the last decade there have been some significant advances in vaccine adjuvants, particularly in relation to their inclusion in licensed products. This was proceeded by several decades in which such advances were very scarce, or entirely absent, but several novel adjuvants have now been included in licensed products, including in the US. These advances have relied upon several key technological insights that have emerged in this time period, which have finally allowed an in depth understanding of how adjuvants work. These advances include developments in systems biology approaches which allow the hypotheses first advanced in pre-clinical studies to be critically evaluated in human studies. This review highlights these recent advances, both in relation to the adjuvants themselves, but also the technologies that have enabled their successes. Moreover, we critically appraise what will come next, both in terms of new adjuvant molecules, and the technologies needed to allow them to succeed. We confidently predict that additional adjuvants will emerge in the coming years that will reach approval in licensed products, but that the components might differ significantly from those which are currently used. Gradually, the natural products that were originally used to build adjuvants, since they were readily available at the time of initial development, will come to be replaced by synthetic or biosynthetic materials, with more appealing attributes, including more reliable and robust supply, along with reduced heterogeneity. The recent advance in vaccine adjuvants is timely, given the need to create novel vaccines to deal with the COVID-19 pandemic. Although, we must ensure that the rigorous safety evaluations that allowed the current adjuvants to advance are not 'short-changed' in the push for new vaccines to meet the global challenge as quickly as possible, we must not jeopardize what we have achieved, by pushing less established technologies too quickly, if the data does not fully support it.