Phase 1/2 randomized, observer-blind clinical trial of a first-generation, mRNA-based vaccine against seasonal influenza and COVID-19 in healthy adults

ABSTRACT

A multicomponent vaccine against seasonal influenza and COVID-19 could reduce disease burden in adults by providing simultaneous protection in a single-dose regimen. The first-generation, mRNA-based, multicomponent mRNA-1073 vaccine, combining antigens encoded by mRNA-1010 (influenza) and mRNA-1273 (COVID-19) vaccines, was investigated in a phase 1/2 clinical trial. This stratified, observer-blinded study randomly assigned healthy adults (18–75 years) to receive mRNA-1073 (25-µg, 50-µg, or 100-µg) + placebo, mRNA-1273 (50-μg) + placebo, mRNA-1010 (50-μg) + placebo, or co-administered mRNA-1010 (50-μg) + mRNA-1273 (50-μg) on day 1. Primary study objectives were safety and reactogenicity. Secondary study objectives assessed humoral immunogenicity against vaccine-matched influenza and SARS-CoV-2 strains at day 29 and all evaluable time points through day 181. An exploratory objective was to further characterize immune responses across the study vaccines. Overall, 550 participants were randomly assigned to receive study vaccination. mRNA-1073 exhibited dose-dependent reactogenicity. Most solicited adverse reactions were grade 1 or 2 in severity; no grade 4 events, serious adverse events related to study vaccination, or deaths were reported. A single dose of mRNA-1073 elicited durable immune responses through 6 months against all vaccine-matched influenza and SARS-CoV-2 strains. Systems serology analysis indicated that mRNA-1073 induced robust, balanced antibody responses with comparable immune profiles to mRNA-1010 + mRNA-1273. mRNA-1073 had an acceptable safety profile and elicited durable immune responses against all vaccine-matched influenza and SARS-CoV-2 strains, supporting ongoing evaluations of mRNA-based multicomponent vaccines that simultaneously protect against seasonal influenza and COVID-19 in a single dose.

Registration: ClinicalTrials.gov identifier: NCT05375838 (https://clinicaltrials.gov/study/NCT05375838).

Introduction

Seasonal influenza viruses and SARS-CoV-2 are respiratory pathogens that represent a major public health concern.^1,2 Seasonal influenza viruses cause approximately one billion cases worldwide each year,¹ while at least 776 million cases of COVID-19 have been reported worldwide since January 2020.³ In the 2023–2024 season in the United States, seasonal influenza and SARS-CoV-2 viruses led to considerable proportions of hospitalized patients being admitted into intensive care units (17.4% and 16.6%, respectively).^4,5 Despite the substantial disease burden, vaccination rates remain suboptimal, with only <50% and <25% of adults in the United States receiving updated 2023–2024 vaccines against influenza and SARS-CoV-2 viruses, respectively, as of May 11, 2024.^6,7 To improve the uptake in vaccinations and streamline the immunization process, the World Health Organization (WHO) has recommended administering available influenza and COVID-19 vaccines together.⁸ Beyond a co-administration approach, a multicomponent vaccine targeting both seasonal influenza and COVID-19 could also help to address disease burden, as this approach could improve immunization accessibility through increasing convenience for recipients, simplifying immunization schedules, and avoiding delays in vaccination⁹ within a single injection.

mRNA-1073 is a first-generation, mRNA-based multicomponent vaccine combining the respective antigens of the original formulation of an investigational seasonal influenza vaccine (mRNA-1010) and a licensed SARS-CoV-2 vaccine mRNA-1273 (Spikevax; Moderna, Inc.; Cambridge, MA, USA). mRNA-1010 contains mRNA encoding hemagglutinin (HA) surface glycoproteins of influenza strains recommended by the WHO and has been investigated in multiple clinical trials. Notably, the original mRNA-1010 formulation (as included in the mRNA-1073 vaccine) was initially tested in phase 1–3 trials,^10–12 but has since been significantly improved and an optimized mRNA-1010 formulation is currently under phase 3 investigation.^13,14 mRNA-1273 is the original monovalent COVID-19 vaccine, authorized for emergency use in 2020 during the COVID-19 pandemic;¹⁵ it contains a single mRNA sequence encoding the spike (S) glycoprotein of ancestral SARS-CoV-2. Both mRNA-based vaccines have independently been shown to induce strong humoral immune responses in adults, with mRNA-1010 showing no safety concerns in a phase 1/2 trial while eliciting robust antibody responses against vaccine-matched influenza A and B strains.^10,11 In the pivotal phase 3 trial, mRNA-1273 was shown to exhibit an acceptable safety profile and efficacy in the prevention of COVID-19 illness and severe disease, and elicited robust humoral immunogenicity against ancestral SARS-CoV-2.^16,17

Here, we report findings from a phase 1/2 trial on the safety, reactogenicity, and immunogenicity of mRNA-1073 in adults aged 18 to 75 years. The primary objective was to evaluate safety and reactogenicity, while secondary objectives were to evaluate humoral immunogenicity against seasonal influenza, as measured by hemagglutination inhibition (HAI), and against SARS-CoV-2, as measured by pseudovirus neutralization assay (PsVNA), through day 181. Recent findings have also suggested that additional antibody mechanisms may contribute to protection against influenza and SARS-CoV-2 infection and disease, including antibody-dependent cellular cytotoxicity associated with postvaccination protection against influenza^18,19 and Fc-mediated effector functions elicited by COVID-19 mRNA vaccines that were resilient to SARS-CoV-2 evolution;²⁰ therefore, a systems serology approach was also applied as an exploratory objective to comprehensively assess humoral immune responses elicited by vaccination.

Methods

Study design and participants

This was a phase 1/2, randomized, stratified, observer-blinded study at 14 sites in the United States that evaluated the safety, reactogenicity, and immunogenicity of mRNA-1073 compared with individually administered and co-administered mRNA-1010 and mRNA-1273 vaccines in adults aged 18 to 75 years (NCT05375838). This report summarizes results after all participants had completed or withdrawn from the study.

Eligible participants were healthy adults aged 18 to 75 years who were fully vaccinated for COVID-19 primary series according to the locally authorized or approved regimen, and their last COVID-19 vaccine (primary series or booster) had been ≥120 days before the randomization visit (or less per local guidance). Inclusion/exclusion criteria are detailed in the Supplement. Participants were randomly assigned (1:2:2:2:2:2) using a randomization allocation schedule generated by the biostatistics department to receive mRNA-1273 (50-μg) + placebo, mRNA-1073 (25-µg, 50-µg, or 100-µg) + placebo, mRNA-1010 (50-μg) + placebo, or co-administered mRNA-1010 (50-μg) + mRNA-1273 (50-μg). Randomization was age-stratified (18–49 years and 50–75 years, balanced across the two age groups within each vaccination group). Details on the randomization and observer-blind conduct of this study are included in the Supplement. Participants received vaccination on day 1, and the final visit was on day 181 (month 6).

The study was conducted in accordance with the protocol, applicable laws, and regulatory requirements, as well as International Council for Harmonization Good Clinical Practice guidelines, and the consensus ethical principles derived from international guidelines, including the Declaration of Helsinki and Council for International Organizations of Medical Sciences International Ethical Guidelines. The protocol was approved by the institutional review board prior to study initiation, and written informed consent was obtained from all participants before enrollment.

Vaccines

mRNA-1073 is a lipid-encapsulated mRNA-based vaccine containing mRNAs encoding for antigens within mRNA-1010 (seasonal influenza) and mRNA-1273 (SARS-CoV-2) vaccines. For this study, mRNA-1010 encoded in equal amounts the wild-type HA for the 4 influenza strains recommended by the WHO for the 2022 Southern Hemisphere season and mRNA-1273 encoded the full-length SARS-CoV-2 prefusion-stabilized S glycoprotein of the ancestral SARS-CoV-2 strain. The ratio of 4 HA to SARS-CoV-2 is the same in all of the doses of mRNA-1073 tested. Additionally, mRNA-1073, mRNA-1010, and mRNA-1273 were all formulated with a common lipid nanoparticle mixture. Placebo was 0.9% sodium chloride. On day 1, vaccines and/or placebo were given intramuscularly; in the co-administration group, mRNA-1010 and mRNA-1273 were given as a single injection, one in each deltoid muscle (left and right arm).

Objectives

The primary objective was to evaluate the safety and reactogenicity of a single dose of study vaccination. Secondary objectives were to evaluate humoral immunogenicity against vaccine-matched seasonal influenza and SARS-CoV-2 strains at day 29 and at all evaluable time points (days 8, 29, and 181). An exploratory objective was to further characterize the immune response across the study vaccines.

Outcomes

Safety end points included solicited local and systemic adverse reactions (ARs) within 7 days after vaccination (Table S1), unsolicited adverse events (AEs) within 28 days after vaccination, and serious AEs (SAEs), AEs of special interest (AESIs), medically attended AEs (MAAEs), and AEs leading to discontinuation from day 1 through the end of the study (day 181; see Supplement for details). Blood samples for immunogenicity assessments were collected on days 1 (baseline), 8, 29, and 181 (end of study). Humoral immunogenicity end points included geometric mean titers (GMTs) or geometric mean concentrations (GMCs) at days 1, 8, 29, and 181; geometric mean fold rises (GMFRs) at days 8, 29, and 181 over day 1; percentage of participants at day 29 with seroconversion (influenza) of serum anti-HA antibodies against vaccine-matched influenza strains measured by HAI assay,¹¹ or seroresponse (SARS-CoV-2) of serum neutralizing antibodies against the vaccine-matched SARS-CoV-2 strain measured by PsVNA or binding antibody (bAb) assay.²¹ Antibody values for the HAI and PsVNA assays reported as below the lower limit of quantification (LLOQ) were replaced by 0.5 × LLOQ; values greater than the upper limit of quantification (ULOQ) were converted to the ULOQ if actual values were not available. Seroconversion was defined as a day 29 titer of ≥1:40 if baseline was <1:10, or a ≥4-fold rise if the baseline was ≥1:10. Seroresponse was defined as a day 29 titer of ≥4-fold if the baseline was at least at the LLOQ, or ≥4 × LLOQ if the baseline titer was <LLOQ. Systems serology analyses were performed as an exploratory objective for additional immunogenicity assessments at days 1 (baseline) and 29 (peak immunogenicity). For systems serology analyses, a multiplex Luminex assay was performed to measure antigen-specific antibody isotypes and Fcγ-receptor (FcγR) binding, as previously described.²² Detailed information on the multiplex Luminex assay, the HAI and PsVNA assays, antigens, and protein production and purification can be found in the Supplement.

Statistical analyses

No formal statistical hypotheses were tested. Sample size was considered sufficient to provide a descriptive summary of the safety and immunogenicity of different study groups. With a sample size of 100 participants in 1 vaccination group, an AE rate of 2% or 3% provided an 85% or 95% power, respectively, to detect at least one participant with an AE.

All safety analyses were descriptive in nature and based on the safety population, defined as all randomly assigned participants who received the study vaccination, except for summary of solicited ARs, which was based on the solicited safety population, defined as all participants in the safety population who contributed any solicited AR data.

All immunogenicity assessments were performed in the per-protocol population, which comprised all randomly assigned participants who received vaccination and complied with injection schedule, with baseline and ≥1 postvaccination time point blood sampling and a day 29 assessment, did not have influenza or SARS-CoV-2 infection at baseline through day 29 (as documented by a positive reverse transcriptase-polymerase chain reaction), and had no major protocol deviation or prohibited prespecified concomitant medication use that impacted the immune response. For GMTs/GMCs and GMFRs, 95% CIs were calculated based on the t distribution of the log-transformed values, then back-transformed to the original scale. The seroconversion rate (SCR) and seroresponse rate (SRR) were determined along with 2-sided 95% CIs using the Clopper–Pearson method. Detailed information on the raw data processing, univariate analysis, and multivariate analysis can be found in the Supplement.

Results

Participants

The first participant was randomly assigned on May 10, 2022, and the study was completed on December 29, 2022; the database lock date was February 24, 2023. A total of 550 participants were randomly assigned to receive vaccination, and most participants (517/550 [94%]) completed the study. The most common reasons for study discontinuation were lost to follow-up (18/550 [3.3%]) and withdrawal of consent by participant (10/550 [1.8%]) (Figure 1). Demographic and baseline characteristics were balanced between vaccination groups (Table S2). The median age of participants was 49 years; 59% of participants were female, 81% were White, 14.3% were Black/African American, and 88.3% were non-Hispanic or -Latino.

Figure 1.

Participant disposition.

All randomly assigned participants who received the study vaccination were included in both the full analysis set and the safety population. The most common reason for exclusion from the per-protocol immunogenicity set was influenza or SARS-CoV-2 infection at baseline through Day 29.

^aParticipants with multiple reasons for exclusion from the per-protocol population were listed under the reason that appeared earliest.

^bNumbers were based on planned vaccination group.

^cParticipants were considered to have completed the study if they completed the final study visit on day 181.

Safety

Solicited adverse reactions

Solicited local ARs were reported in 77.6%, 81.6%, 89.1%, and 77.6–92.0% of participants in the mRNA-1273, mRNA-1010, co-administration group, and mRNA-1073 arms, respectively, while solicited systemic ARs were reported in 63.3%, 71.4%, 86.1%, and 64.3–80.0% of participants in the same arms. The frequency of solicited local and systemic ARs within 7 days after mRNA-1073 vaccination increased in a dose-dependent manner. Most solicited ARs were grade 1 or 2 in severity (Figure 2); no grade 4 solicited ARs were reported in any vaccination group. The most common local solicited AR was injection site pain; fatigue, myalgia, and headache were the most common solicited systemic ARs (Figure 2). Across vaccination groups, the median duration of solicited ARs was 2 to 3 days. A higher proportion of participants in the ≥18 to ≤49 years age group reported solicited ARs compared to the ≥50 to ≤75 years age group.

Figure 2.

Participants with solicited (A) Local and (B) Systemic adverse reactions within 7 days after vaccination (solicited safety population).

Number of participants: mRNA-1273 50 µg + placebo, n = 49; mRNA-1010 50 µg + placebo, n = 98; mRNA-1010 50 µg + mRNA-1273 50 µg, n = 101; mRNA-1073 25 µg + placebo, n = 100; mRNA-1073 50 µg + placebo, n = 98; mRNA-1073 100 µg + placebo, n = 100.

Unsolicited adverse events

Within 28 days of study vaccination, a total of 94 participants (17.2%) reported unsolicited AEs across vaccination groups (Table 1); 3.1% of unsolicited AEs were assessed as related to study vaccination and were primarily associated with reactogenicity. Throughout the study (day 181), severe AEs were reported by 4 participants, were all considered related to study vaccination by the investigator, and all ultimately resolved: fatigue (n = 1; mRNA-1073 100 µg), myalgia (n = 1; mRNA-1073 100 µg), arthralgia (n = 1; co-administration group), and severe diarrhea (n = 1; co-administration group). A total of 6 SAEs were reported by 4 participants throughout the study; none were considered related to vaccination by the investigator. One AESI of increased aspartate aminotransferase (AST) in 1 (1.0%) mRNA-1073 25 µg recipient was investigator-assessed as related to study vaccination; the participant reported grade 1 AST increased at 8 days after vaccination that resolved after 17 days. No events of anaphylaxis or myocarditis, pericarditis, or myopericarditis were reported in any vaccination group. Four MAAEs reported by 3 participants were considered related to vaccination by the investigator: severe diarrhea (n = 1; co-administration group; resolved after 4 days), injection site lymphadenopathy (n = 1; mRNA-1073 50 µg; resolved after 64 days), and AST increased (described as an AESI above; n = 1; mRNA-1073 25 µg) and alanine aminotransferase increased (n = 1; mRNA-1073 25 µg; resolved after 11 days). No participants discontinued from the study due to an AE, and no deaths were reported throughout the study.

Table 1.

Summary of unsolicited adverse events after vaccination (safety population).

	mRNA-1273 50 µg + placebo (N = 49)	mRNA-1010 50 µg + placebo (N = 99)	mRNA-1010 50 µg + mRNA-1273 50 µg (N = 101)	mRNA-1073 25 µg + placebo (N = 100)	mRNA-1073 50 µg + placebo (N = 98)	mRNA-1073 100 µg + placebo (N = 100)
Within 28 d after vaccinationa
Regardless of relationship, n (%)
Any AE	7 (14.3)	21 (21.2)	14 (13.9)	22 (22.0)	11 (11.2)	19 (19.0)
Severe	0	0	2 (2.0)	0	0	2 (2.0)
SAE	1 (2.0)	0	0	0	0	0
Fatal	0	0	0	0	0	0
MAAE	3 (6.1)	13 (13.1)	7 (6.9)	12 (12.0)	9 (9.2)	13 (13.0)
Leading to study discontinuation	0	0	0	0	0	0
AESI	0	1 (1.0)	0	1 (1.0)	0	1 (1.0)
Related to study vaccination,b n (%)
Any AE	0	6 (6.1)	3 (3.0)	4 (4.0)	1 (1.0)	3 (3.0)
Severe	0	0	2 (2.0)	0	0	2 (2.0)
SAE	0	0	0	0	0	0
Fatal	0	0	0	0	0	0
MAAE	0	0	1 (1.0)	1 (1.0)	1 (1.0)	0
Leading to study discontinuation	0	0	0	0	0	0
AESI	0	0	0	1 (1.0)	0	0
Within 6 months after vaccinationa
Regardless of relationship, n (%)
SAE	2 (4.1)	1 (1.0)	0	0	1 (1.0)	0
MAAE	13 (26.5)	38 (38.4)	32 (31.7)	44 (44.0)	34 (34.7)	34 (34.0)
AESI	0	2 (2.0)	0	1 (1.0)	0	1 (1.0)
Leading to study discontinuation	0	0	0	0	0	0
Related to study vaccination,b n (%)
SAE	0	0	0	0	0	0
MAAE	0	0	1 (1.0)	1 (1.0)	1 (1.0)	0
AESI	0	0	0	1 (1.0)	0	0
Leading to study discontinuation	0	0	0	0	0	0

Abbreviations: AE, adverse event; AESI, adverse event of special interest; MAAE, medically attended adverse event; SAE, serious adverse event.

^aAn AE was defined as any event not present before study vaccination or any event already present that worsened in intensity after vaccination.

^bPer the study protocol, the investigator assessed each occurrence of an AE and reported it as related (a reasonable possibility) or not related (not a reasonable possibility) to study vaccination.

Immunogenicity

HAI (influenza) and PsVNA (SARS-CoV-2) responses

HAI GMTs and PsVNA GMCs were similar for vaccination groups at baseline. A single dose of mRNA-1073 (all dose levels) increased HAI GMTs (Figure 3(A)) against all influenza strains (A/H1N1, A/H3N2, B/Victoria, and B/Yamagata) and increased PsVNA GMCs against SARS-CoV-2 at day 29 (Figure 3(B)). Overall, HAI GMTs (Figure 3(A)) and SCRs (Figure S1) for all mRNA-1073 dose levels at day 29 were numerically lower than those elicited by co-administered mRNA-1010 + mRNA-1273 for all influenza strains. PsVNA GMCs (Figure 3(B)) and SRRs (Figure S1) against SARS-CoV-2 at day 29 were generally similar between mRNA-1073 vaccine groups and the co-administration group. Responses declined but remained above baseline through day 181 (Figures S1 and S2).

Figure 3.

(A) Influenza HAI GMTs and GMFRs and (B) SARS-CoV-2 PsVNA GMCs and GMFRs at day 1 and day 29 after vaccination (per-protocol immunogenicity population).

HAI GMTs with associated 95% CIs against influenza A or B strains are shown at day 1 (baseline) and day 29. GMFRs at day 29 from day 1 are shown above each day 29 GMT bar plot. GMTs are shown for A/H1N1 (LLOQ: 10, ULOQ: 1280), A/H3N2 (LLOQ: 10, ULOQ: 2560), B/Victoria (LLOQ: 10, ULOQ: 640), and B/Yamagata (LLOQ: 10, ULOQ: 2560). Antibody values reported as below LLOQ were replaced by 0.5 × LLOQ; values greater than ULOQ were converted to the ULOQ if actual values were not available.

PsVNA GMCs with associated 95% CIs against SARS-CoV-2 are shown at day 1 (baseline) and day 29. GMRs at day 29 from day 1 are shown above each day 29 GMC bar plots. GMCs are shown for ancestral SARS-CoV-2 (LLOQ: 10, ULOQ: 111433). Antibody values reported as below LLOQ were replaced by 0.5 × LLOQ; values greater than ULOQ were converted to the ULOQ if actual values were not available.

Abbreviations: CI, confidence interval; GMC, geometric mean concentration; GMFR, geometric mean fold rise; GMT, geometric mean titer; HAI, hemagglutination inhibition; LLOQ, lower limit of quantification; PsVNA, pseudovirus neutralization assay; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; ULOQ, upper limit of quantification.

Influenza and SARS-CoV-2 binding antibody responses

Based on systems serology analyses, a single dose of mRNA-1073 and co-administered mRNA-1010 + mRNA-1273 induced robust SARS-CoV-2 and influenza binding antibody responses at day 29 (Figure 4). A comparison of fold change increases in immunoglobulin (Ig) G1 levels specific to the SARS-CoV-2 S protein, as well as to the influenza HA protein (A/H1N1, A/H3N2, B/Victoria, and B/Yamagata), at day 29 compared with baseline indicated comparable robust IgG1 responses across mRNA-1073 (all dose levels) and co-administration vaccination groups for each antigen (Figure 4(A)). As expected, antigen-specific IgA and IgM antibody levels were induced to a lower extent following vaccination compared with IgG1, with the highest fold changes observed in the mRNA-1073 50-µg group (Figure 4(B,C)).

Figure 4.

Influenza and SARS-CoV-2–specific (A) IgG1, (B) IgA, and (C) IgM responses to mRNA-1073 and co-administration of mRNA-1010 + mRNA-1273.

IgG1, IgA, and IgM responses specific to SARS-CoV-2 WT spike, as well as influenza A/Wisconsin/588/2019 (H1N1), A/Darwin/9/2021 (H3N2), B/Austria/1359417/2021 (B/Victoria lineage), and B/Phuket/3073/2013 (B/Yamagata lineage) HAs were measured at day 1 (baseline) and day 29 (peak immunogenicity). P values were derived from the paired Wilcoxon test with Benjamini–Hochberg (BH) adjustment. Results were filtered to those individuals who had values at both time points. Ratio shown in blue, calculated as 10(log₁₀(D29)-log₁₀ (Baseline)).

Abbreviations: co-ad, co-administration of mRNA-1010 + mRNA-1273; HA, hemagglutinin; Ig, immunoglobulin; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; WT, wild-type.

Given the limited differences observed in isotype levels across the vaccination groups and to illustrate the breadth of response, heatmaps were generated for each dose level group of mRNA-1073 and the co-administration group at day 1 (baseline) and day 29 across different subdomains of the SARS-CoV-2 S protein of ancestral and different variants of concern (VOCs), as well as different influenza A and B strain HAs (circulating between 1999 and 2021). The heatmap illustrated a strong heterogeneity in baseline antigen-specific IgG1 levels across vaccine recipients as well as the robust induction of IgG1 at day 29 (peak immunogenicity; Figure 5(A)). More consistent induction of IgG1 responses and breadth were observed across all mRNA-1073 dose levels compared with the co-administration group. Additionally, summary polar plots were generated for each vaccination group across all antigens, capturing the median IgG1 response for each antigen per vaccination group at days 1 and 29 (Figure 5(B)). Similar patterns of immunodominance were observed across vaccination groups, albeit higher ancestral SARS-CoV-2 S, receptor-binding domain, and S1 domain-specific IgG1 responses were observed in the mRNA-1073 50-µg group. The most balanced and broad responses were observed in the mRNA-1073 50-µg and co-administration groups.

Figure 5.

Breadth of influenza and SARS-CoV-2–specific IgG1 response to mRNA-1073 or co-administration of mRNA-1010 + mRNA-1273.

(A) Induction of antigen-specific IgG1 from day 1 (baseline) to day 29. MFI values were log₁₀ transformed, Z-scored across all vaccine arms and visits, and visualized as a heatmap.

(B) IgG1 responses to each antigen on day 1 (baseline) and day 29 across all vaccination groups are presented as median values and normalized to the 100th percentile. The solid black line indicates a separation between SARS-CoV-2 and influenza HA antigens.

Influenza HA antigens: A/Wisconsin/588/2019 (H1N1), A/New Caledonia/20/1999 (H1N1), A/Darwin/9/2021 (H3N2), A/Hong Kong/4108/2014 (H3N2), A/Singapore/INFIMH-16-0019/2016 (H3N2), A/Newcastle/2021 (H3N2), B/Austria/1359417/2021 (B/Victoria lineage); B/Brisbane/60/2008 (B/Victoria lineage), B/Colorado/06/2017 (B/Victoria lineage), B/Phuket/3073/2013 (B/Yamagata lineage).

Abbreviations: co-ad, co-administration of mRNA-1010 + mRNA-1273; HA, hemagglutinin; Ig, immunoglobulin; MFI, median fluorescence intensity; NTD, N-terminal domain; RBD, receptor-binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; VOC, variant of concern; WT, wild-type.

Influenza and SARS-CoV-2 functional IgG antibody responses

To assess the functionality of the IgG antibodies induced following vaccination, binding to various FcγR was determined by the Luminex assay. A significant expansion of FcγR2a, FcγR2b, FcγR3a, and FcγR3b bAbs was observed across the SARS-CoV-2 and influenza A strains at day 29 (Figure 6(A)). Variable augmentation of FcγR binding was observed for the B/Victoria HA antibody responses, while limited FcγR-binding was observed for the B/Yamagata HA responses.

Figure 6.

Kinetics of FcγR-binding and variation in the dataset at day 29 for all features specific to antigens included in mRNA-1073.

(A) Induction of FcγR binding from day 1 (baseline) to day 29. IgG binding to FcγR2A, FcγR2B, FcγR3A, and FcγR3B specific to SARS-CoV-2 WT spike, as well as influenza A/Wisconsin/588/2019 (H1N1), A/Darwin/9/2021 (H3N2), B/Austria/1359417/2021 (B/Victoria lineage), and B/Phuket/3073/2013 (B/Yamagata lineage) HAs were measured. P values were derived from the paired Wilcoxon test with Benjamini–Hochberg (BH) adjustment. Results were filtered to those individuals who had values at both time points. Fold change is shown in blue, calculated as log₁₀(D29) − log₁₀(Baseline).

(B) A PCA was used to model the differences between individuals who received different doses of mRNA-1073 (25 µg, 50 µg, and 100 µg), and the differences between individuals who received either mRNA-1073 100ug or co-administered mRNA-1010 + mRNA-1273. Features were Z-scored, samples with more than 20% missing data were excluded (n excluded = 54), and features with more than 20% missing data were excluded (n excluded = 1: IgG4_H3 Darwin 2020). Other missing data were imputed using kNN imputation.

Abbreviations: FcγR, Fcγ-receptor; HA, hemagglutinin; Ig, immunoglobulin; kNN, k-nearest neighbors; PC, principal component; PCA, principal component analysis; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; WT, wild-type.

To determine whether different dose levels of mRNA-1073 induced different overall SARS-CoV-2 and influenza antibody profiles, all isotype, subclass, and FcγR binding data were combined and a principal component analysis was performed. The global humoral responses were nearly identical across all arms (Figure 6(B)), suggesting similar quantitative and qualitative immunogenicity across the mRNA-1073 dose levels. Furthermore, direct comparison of mRNA-1073 100 µg and the co-administered mRNA-1010 + mRNA-1273 also revealed comparable overall antibody profiles across the vaccination groups (Figure 6(B)).

Discussion

This was among the first phase 1/2 clinical trials to evaluate the safety, reactogenicity, and immunogenicity of an mRNA-based multicomponent vaccine against seasonal influenza and SARS-CoV-2 in healthy adults. This first-generation multicomponent mRNA-based vaccine simultaneously encodes HA antigens of WHO-recommended seasonal influenza strains and the S glycoprotein of ancestral SARS-CoV-2. No safety concerns with mRNA-1073 vaccination were identified. The vaccine exhibited dose-dependent reactogenicity, with better tolerability at doses below 100 µg. Most solicited ARs were grade 1 or 2 in severity; the incidence of grade 3 solicited ARs was highest in the mRNA-1073 100 µg group. Reactogenicity of mRNA-1073 (100 µg) was generally similar to the co-administered mRNA-1010 + mRNA-1273, which were more reactogenic than the lower doses of mRNA-1073 (25 µg and 50 µg). No grade 4 events, SAEs related to the study of vaccinations, or deaths were reported.

mRNA-1073 elicited humoral immune responses against all 4 influenza strains and SARS-CoV-2 at day 29, which declined through 6 months yet remained above baseline, with similar immunogenic responses observed across dose levels. Although HAI GMTs were lower with mRNA-1073 than with the co-administered mRNA-1010 + mRNA-1273 vaccines for all vaccine-matched influenza A and B strains at day 29, the trend observed through 6 months was comparable between vaccination groups, with HAI GMTs remaining above the 1:40 threshold associated with 50% reduced risk of infection in adults.²³ PsVNA GMCs against SARS-CoV-2 were comparable across mRNA-1073 vaccination groups through 6 months. These findings show that a multicomponent mRNA-based vaccine can elicit durable antibody responses to the respective pathogens up to 6 months, supporting this immunization approach against seasonal influenza and SARS-CoV-2 in adults, particularly as development advances to next-generation vaccine candidates. Future studies establishing long-term durability and efficacy are warranted.

This trial also comprehensively evaluated the antibody-mediated immune response elicited by multicomponent mRNA-based vaccination. HAI is a well-understood predictor of protection against influenza infections, acting as a surrogate marker of viral blockade.²⁴ However, more recent findings suggest that additional antibody functions induced by vaccines may also contribute to protection against influenza. For instance, the ability of influenza-specific antibodies to engage innate immune cells, particularly through antibody-dependent cellular cytotoxicity, has been associated with protection both in preclinical models²⁵ and postvaccination studies in humans.^18,19 Similarly, COVID-19 mRNA vaccines have been found to induce robust Fc-mediated effector functions that remain effective despite SARS-CoV-2 viral evolution in the context of the COVID-19 pandemic.^26,27 Standard methods that assess antibody response measure binding or neutralizing antibody titers, but do not fully characterize the quality of antibodies.²⁸ Systems serology is a multivariate approach to provide comprehensive information on antibody features and functions, thereby providing important knowledge on antibody functions that may contribute to protection, which is important for vaccine development.^28,29 In this trial, systems serology analysis identified that mRNA vaccination (at all dose levels) induced robust IgG1 responses across SARS-CoV-2 and influenza antigens, with IgA and IgM responses induced to a lower extent. Additionally, significant influenza-specific IgA responses were observed, especially at the mRNA-1073 50-µg dose. These antigen-specific responses suggest that all mRNA-1073 vaccination groups elicit robust humoral immunity. An examination of the breadth of response indicated that mRNA-1073 induced antibody responses across different SARS-CoV-2 VOCs and circulating influenza A and B strains with similar overall IgG1 profiles in the mRNA-1073 and co-administration groups. The interaction between Fc receptors and antibodies plays an important role in vaccine-mediated protection against both SARS-CoV-2 and influenza as it is indicative of an additional protective mechanism.²⁷ An assessment of the influence of mRNA-1073 and mRNA-1010 + mRNA-1273 co-administration on the functional properties of vaccine-induced antigen-specific antibodies indicated that mRNA-1073 elicited an increase in IgG antibody binding to FcγR for SARS-CoV-2 and influenza A strains with comparable immune profiles to the co-administration group. Overall, these results indicate that multicomponent vaccination induced antibody responses to SARS-CoV-2 VOCs and influenza strains, as well as IgG antibody binding to FcγRs, suggesting that multicomponent vaccination may provide persistent protection and reduce disease severity comparable to co-administration.^26,27

The safety and immunogenicity data for this first-generation multicomponent vaccine support the use of the mRNA vaccine platform in a combinatorial vaccine approach against respiratory viruses, which could provide broader protection against multiple respiratory viruses within a single injection. A next-generation multicomponent vaccine against seasonal influenza and SARS-CoV-2 (mRNA-1083) has since been developed and has progressed to phase 3 clinical investigation.^30,31 The mRNA-1083 vaccine is an mRNA-based vaccine that incorporates improvements to seasonal influenza and investigational COVID-19 vaccine formulations. In particular, the vaccine combines the antigen designs of an optimized formulation of mRNA-1010 that has shown improved immune responses against influenza B strains in a phase 3 trial.^10,14 Further, mRNA-1083 reflects the antigen design of a next-generation COVID-19 vaccine (mRNA-1283) that contains mRNAs encoding the N-terminal and receptor-binding domains of the SARS-CoV-2 S proteins. Compared to mRNA-1273, this next-generation COVID-19 vaccine has been shown to induce higher antibody titers and noninferior efficacy against COVID-19 with a comparable tolerability profile.³²

Study strengths include a randomized, observer-blind study design and the use of co-administered and stand-alone vaccines as comparators. Limitations include the relatively small number of participants enrolled in the study and the predominantly White, US-based participant population, which may limit the generalizability of the results to other geographical regions and the broader population. Additionally, while breadth based on nAb titers may have given further information, this study assessed breadth based on bAb titers only. For SARS-CoV-2, IgG bAb titers to the S glycoprotein are known to correlate well with neutralization titers; however, this correlation is not well established for influenza. In conclusion, as a first-generation multicomponent vaccine, mRNA-1073 had an acceptable safety profile and elicited durable immune responses against all vaccine-matched influenza strains and SARS-CoV-2. Furthermore, systems serology analysis indicated that mRNA-1073 induced robust antibody responses and elicited antibody binding to FcγRs, with comparable immune profiles to co-administered mRNA-1010 + mRNA-1273. These data support ongoing evaluations of mRNA-based multicomponent vaccines that simultaneously protect against seasonal influenza and SARS-CoV-2 in a single dose.

Biographies

Amanda K. Rudman Spergel, a board-certified Internist and Allergist/Immunologist, was a Director of Clinical Development for Infectious Disease at Moderna Inc., where she led clinical trials in the latent virus vaccine development program. Before working in that therapeutic area, Dr. Rudman Spergel concentrated on respiratory virus vaccine development; she led Phase 1 to 3 clinical trials focused on seasonal influenza and influenza/COVID combination vaccines. Prior to joining Moderna Inc., Dr. Rudman Spergel was a physician in the Division of Allergy, Immunology, and Transplantation at the National Institute of Allergy and Infectious Diseases, the National Institutes of Health, and oversaw clinical trials focused on atopic diseases and allergic mechanisms.

Christine A. Shaw is a Vice President and Portfolio Head of Infectious Diseases at Moderna, Inc., with oversight of vaccine development programs including COVID-19, influenza, respiratory combination vaccines, and others. In her tenure at Moderna, Inc., she has also held other roles in Research and Development, including that of a Program Leader for multiple vaccine programs. Prior to joining Moderna, Inc., Christine was involved in RSV vaccine research in the pharmaceutical industry. Christine has a PhD in Microbiology and Molecular Genetics.

Funding Statement

This work was funded by Moderna, Inc.

Disclosure statement

Carole Henry, Raffael Nachbagauer, Paulina Kaplonek, Andrei Avanesov, Harry Bertera, Deniz Cizmeci, Avi Collins, Alan Embry, Ruiting Guo, Xuezhou Mao, Alicia Pucci, Sarah Shao, Jessica Shih-Lu-Lee, Wen-Han Yu, and Christine A. Shaw are employees of and shareholders in Moderna, Inc.

Amanda K. Rudman Spergel is a former employee of Moderna, Inc. and is a shareholder in Moderna, Inc. Eleanor Astley, Galit Alter, Lizbeth Carmona, and Jintanat Ananworanich are former employees of Moderna, Inc.

Daniel Brune, Laurence Chu, and Muhammad Irfan have no conflicts of interest to disclose.

Consent to participate

Written informed consent was obtained from all participants before enrollment.

Data availability statement

Access to participant-level data presented in this article and supporting clinical documents with external researchers who provide methodologically sound scientific proposals will be available upon reasonable request and subject to review from 2 years after study completion. Such requests can be made to Moderna Inc., 325 Binney Street, Cambridge, MA 02142 <<data_sharing@modernatx.com>>. A materials transfer and/or data access agreement with the sponsor will be required for accessing shared data. All other relevant data are presented in the paper. The protocol is available online at ClinicalTrials.gov: NCT05375838.

Ethical declarations

The study was conducted in accordance with the protocol, applicable laws, and regulatory requirements, as well as International Council for Harmonization Good Clinical Practice guidelines, and the consensus ethical principles derived from international guidelines, including the Declaration of Helsinki and Council for International Organizations of Medical Sciences International Ethical Guidelines. The protocol was approved (Pro00061956) by the central institutional review board (Advarra, Inc. Columbia, MD, 21044, USA) prior to study initiation. Written informed consent was obtained from all participants before enrollment.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21645515.2025.2589644.