This study allows to evaluate the strength and duration of immune responses between annual receipt of standard inactivated vaccine and alternative potent vaccines, including annual receipt of adjuvanted inactivated vaccine, annual receipt of high-dose inactivated vaccine, annual receipt of recombinant HA vaccine, and the alternate combinations of the former three vaccines over four years, for identifying improved vaccination strategies for influenza vaccination in older adults in a location experiencing a subtropical pattern in influenza activity.
Background: The typical vaccination strategy of annual administration with inactivated trivalent influenza vaccine (TIV) or quadrivalent influenza vaccine (QIV) may provide suboptimal protection to older adults in a location with prolonged periods of influenza activity because of the weaker immune response of older adults to vaccination and because of post-vaccination waning in protection over the course of a year. We hypothesize that in a subtropical or tropical location with prolonged circulation of influenza viruses, the higher antibody titers over years achieved after receipt of annual high-dose vaccine, MF59-adjuvanted vaccine or recombinant haemagglutinin (HA) vaccine, or different vaccination strategies of their combinations with or without the standard vaccine, might lead to greater protection than annual receipt of standard vaccines. Aim: To test the immune profiles over time of older adults following different influenza vaccination strategies. Design and subjects: Initially a 4-year immunogenicity study with a randomized controlled design among 2200 older adults aged 65-82 years. We will enroll participants who are willing to receive annual influenza vaccination from the general community including community centres and day-care centres. Eligible individuals will be randomly allocated to ten intervention groups (i.e. annual standard QIV, annual MF59-adjuvanted TIV, annual high-dose TIV, annual recombinant-HA QIV, and six combinations of their alternate annual use) consisting of four rounds of vaccination before each winter influenza season and followed up for 4 years. For each round of vaccination, blood samples for immunological tests will be collected before vaccination and 30 and 182 days after vaccination in all participants, and also at 7, 91 and 273 days after vaccination in a subset of 10% of the participants. Acute illnesses among participants will be monitored by active surveillance efforts during influenza seasons. The vaccine formulation in each round of vaccination will be updated for each season according to WHO recommendations. Study extension: In years 5-8, all participants will receive the recombinant-HA QIV once per year before each winter influenza season, and their receipt of COVID-19 vaccines will also be recorded. Samples will be collected at the same timepoints to monitor immune responses to influenza vaccination and how responses are affected by prior vaccination history. Main outcome measures: Antibody titers measured by haemagglutination-inhibition assays, which is an established correlate of protection, in addition to other measurements on humoral and cell-mediated immune responses in the ten intervention groups each year.
0.5mL FluQuadri®, Sanofi Pasteur, containing 60μg antigen - 15μg for each influenza strain included - with strains recommended by the WHO for the northern hemisphere formulation.
0.5mL FLUAD(TM), Seqirus containing 45μg antigen; 15μg for each influenza strain included and MF59C.1 adjuvant (MF59®) with strains recommended by the WHO for the northern hemisphere formulation.
0.5mL Fluzone® High-Dose, Sanofi Pasteur containing 180μg antigen; 60μg for each influenza strain included with strains recommended by the WHO for the northern hemisphere formulation.
The University of Hong Kong
Hong Kong, China
Difference in antibody titres
The difference in antibody titres of participants measured by haemagglutination-inhibition (HAI) assay, evaluated by (1) the proportion of participants who achieve a target rise in antibody titre against each of the vaccine strains at 30 days, and (2) the geometric mean titre (GMT) ratios between the two groups against each of the vaccine strains at 30 days and 182 days. (The targeted rise in antibody titre is defined as the percentage of subjects with either a pre-vaccination HAI titre \<10 and a post-vaccination HAI titre ≥40, or a pre-vaccination HAI titre ≥10 and a minimum four-fold rise in post-vaccination HAI antibody titre.)
Time frame: 30 and 182 days after each vaccination
Seroprotection
The proportion of participants who achieve seroprotection defined as an HAI titre ≥40 after each vaccination before the winter seasons.
Time frame: 30 days after each vaccination
CMI responses
The vaccine-induced influenza-specific CD4+ and CD8+ T cell responses 7 days post- vaccination, proxy by anti-viral IFNγ production evaluated by Intracellular Cytokine Staining (ICS) assay. Responses for these and other relevant biomarkers are compared to baseline at the time of vaccination.
Time frame: . 7 days after each vaccination
Adverse events
The rate of adverse events within 30 days after vaccination for each round of vaccination.
Time frame: 30 days after each vaccination
PCR confirmed infection
The rate of PCR-confirmed influenza infection in each round of the study.
Time frame: 182 days after each vaccination
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Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
PREVENTION
Masking
TRIPLE
Enrollment
1,861
0.5mL Flublok®, Protein Sciences Corporation containing 180μg antigen, 45μg for each influenza strain included with strains recommended by the WHO for the northern hemisphere formulation.