Immunogenicity and safety of mRNA-based seasonal influenza vaccines encoding hemagglutinin and neuraminidase

Categories: Disease & Virus

July 2, 2025

Trial design and participants

This phase 1/2, randomized, observer-blind trial (ClinicalTrials.gov, NCT05333289) was conducted at 15 sites in the United States during the northern hemisphere spring of 2022 and was designed to evaluate the safety, reactogenicity, and immunogenicity of mRNA-1020 and mRNA-1030 candidate seasonal influenza vaccines in healthy adults. Medically stable adults aged 18−75 years with a body mass index of 18−35 kg/m² were eligible to participate in this study. Full inclusion and exclusion criteria are provided in the study protocol, available online with the full text of this article.

Eligible participants were randomly allocated in a 1:1:1:1:1:1:1:1 ratio to eight vaccine groups: mRNA-1020 at three dose levels (50, 100, or 150 μg), mRNA-1030 at three dose levels (25, 50, or 100 μg), an mRNA-based HA comparator (mRNA-1010 50 μg), or a licensed quadrivalent recombinant vaccine (Flublok, Sanofi Pasteur Inc., Bridgewater, NJ, USA) as an HA-only active comparator (Supplementary Fig. 1). Random allocation was stratified by age (18−49 vs. 50−75 years) to ensure balance of the two age groups within each vaccine group. The sponsor’s biostatistics department or designee generated the randomized allocation schedule for vaccine group assignment using interactive response technology. Vaccine dose preparation and administration were performed by unblinded personnel who had no other role in the conduct of the trial.

This trial was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines of the International Council for Harmonization, and the protocol was approved by the Advarra central institutional review board (protocol number Pro00061700). All participants provided written informed consent. Moderna, Inc., was responsible for the design of the trial and for the analysis of data.

Vaccines

The mRNA vaccines tested in this study were lipid nanoparticle dispersions containing mRNA encoding surface glycoproteins of each of the four strains recommended by the World Health Organization for 2021/2022 northern hemisphere vaccines (A/Wisconsin/588/2019 [H1N1]; A/Cambodia/e0826360/2020 [H3N2]; B/Washington/02/2019 [B/Victoria lineage]; B/Phuket/3073/2013 [B/Yamagata lineage]). mRNA-1020 and mRNA-1030 each contained mRNA encoding four HA and four NA antigens (HA:NA mass ratio of 1:1 and 3:1, respectively), whereas mRNA-1010 contained mRNA encoding four HA antigens only (Supplementary Table 5). The licensed recombinant vaccine (180 µg) contained four recombinant HA proteins (each 45 µg). All vaccines were administered at a 0.5 mL volume as a single intramuscular injection into the deltoid muscle on day 1.

Trial objectives

The primary objectives of this study were to evaluate the safety and reactogenicity of mRNA-1020, mRNA-1030, and mRNA-1010 and to evaluate the antibody responses elicited by mRNA-1020, mRNA-1030, and mRNA-1010 against vaccine-matched influenza A and B strains at day 29. The secondary objective of this study was to evaluate the antibody responses elicited by mRNA-1020, mRNA-1030, and mRNA-1010 against vaccine-matched influenza A and B strains at all evaluable immunogenicity time points up to the end of the study (day 181).

Safety

The primary safety/reactogenicity end points of this study were the frequency and grade of each solicited local and systemic adverse reaction (AR) within 7 days after vaccination; the frequency and severity of any unsolicited adverse events (AEs) within 28 days after vaccination; and the frequency of any AEs that were serious (SAEs), of special interest (AESI), medically attended (MAAEs), or led to discontinuation from study participation from day 1 through to the end of the study (day 181). An eDiary solicited daily participant reporting of ARs using a structured checklist on the day of vaccine administration and on the following 6 days. Unsolicited AEs were recorded after vaccination at clinic visits and during safety phone calls throughout the study. Blood collection for safety laboratory testing was performed at screening (up to 28 days prior to vaccination) and on day 8. Participants with influenza-like illness symptoms were instructed to notify the site in order to undergo medical evaluation and nasal swabs for RT-PCR testing.

Immunogenicity

Blood collection for immunogenicity was performed on days 1, 8, 29, and 181 (end of the study). Serum anti-HA antibody levels were measured by a qualified hemagglutination inhibition (HAI) assay, and NA-specific antibody levels were measured by a qualified NA inhibition (NAI) assay (Supplementary Methods). The primary immunogenicity end points included the geometric mean titer (GMT) of anti-HA and anti-NA antibodies against vaccine-matched influenza A and B strains at baseline (day 1) and day 29; geometric mean fold rise (GMFR) of anti-HA and anti-NA antibodies at day 29 versus baseline; the percentage of participants with seroconversion at day 29 (defined as a titer of ≥ 1:40 [if baseline was < 1:10] or a ≥ four-fold rise in titer [if baseline was ≥ 1:10]) measured by the HAI assay; and the percentage of participants with ≥two-fold, ≥three-fold, and ≥four-fold rise in titers at day 29 as measured by the NAI assay. The secondary immunogenicity end points included the GMT and GMFR (versus baseline) of anti-HA or anti-NA antibodies at all evaluable time points.

Statistical analyses

The sample size for this study was not driven by statistical assumptions for formal hypothesis testing. A total of approximately 560 participants, with 70 participants randomly assigned into each vaccine group, was planned and considered to be sufficient to provide descriptive safety and immunogenicity of different dose levels of mRNA-1020 or mRNA-1030. Sex of participants was not considered in the study design and was determined based on self-report.

The 95% CIs for GMT and GMFR were calculated based on the t distribution of the log-transformed values, then back-transformed to the original scale. HAI seroconversion rate and the percentage of participants with ≥two-fold, ≥three-fold, and ≥four-fold rise in NAI titers were provided with a two-sided 95% CI using the Clopper-Pearson method. Antibody values below the lower limit of quantitation (LLOQ) were replaced by 0.5 × LLOQ. Antibody values above the upper limit of quantitation (ULOQ) were converted to the ULOQ. Missing safety and immunogenicity data were not imputed. Statistical analyses were performed using SAS version 9.4 or higher.