Immunogenicity and reactogenicity of intradermal mRNA-1273 SARS-CoV-2 vaccination: a non-inferiority, randomized-controlled trial

Abstract

Fractional dosing can be a cost-effective vaccination strategy to accelerate individual and herd immunity in a pandemic. We assessed the immunogenicity and safety of primary intradermal (ID) vaccination, with a 1/5th dose compared with the standard intramuscular (IM) dose of mRNA-1273 in SARS-CoV-2 naïve persons. We conducted an open-label, non-inferiority, randomized controlled trial in the Netherlands between June and December 2021. One hundred and fifty healthy and SARS-CoV-2 naïve participants, aged 18-30 years, were randomized (1:1:1) to receive either two doses of 20 µg mRNA-1273 ID with a standard needle (SN) or the Bella-mu® needle (BM), or two doses of 100 µg IM, 28 days apart. The primary outcome was non-inferiority in seroconversion rates at day 43 (D43), defined as a neutralizing antibody concentration threshold of 465 IU/mL, the lowest response in the IM group. The non-inferiority margin was set at -15%. Neutralizing antibody concentrations at D43 were 1789 (95% CI: 1488-2150) in the IM and 1263 (951-1676) and 1295 (1020-1645) in the ID-SN and ID-BM groups, respectively. The absolute difference in seroconversion proportion between fractional and standard-dose groups was -13.95% (-24.31 to -3.60) for the ID-SN and -13.04% (-22.78 to -3.31) for the ID-BM group and exceeded the predefined non-inferiority margin. Although ID vaccination with 1/5th dose of mRNA-1273 did not meet the predefined non-inferior criteria, the neutralizing antibody concentrations in these groups are far above the proposed proxy for protection against severe disease (100 IU/mL), justifying this strategy in times of vaccine scarcity to accelerate mass protection against severe disease.

Fig. 1. Flowchart of inclusions.

Among the 141 participants receiving a second vaccination, 7 participants were excluded from the immunogenicity analysis afterward due to seropositivity for IgG anti-S1 or anti-N at baseline, indicating an earlier unrecognized SARS-CoV-2 infection. One of them was one of the two participants who ended the study prematurely due to dizziness. ID intradermal, IM intramuscular, D day, M months.

Fig. 2. SARS-CoV-2 specific immune responses.

a Virus neutralization concentration in international units per mL. Horizontal dotted lines represent the LLoD (=15.26 IU/mL). Results below the LLoD were arbitrarily set to LLoD/2. b Neutralization concentration fold change. The dashed line indicates a factor change of 1 (no increase or decrease). Horizontal lines represent the geometric mean + 95% CI of the geometric mean. c SARS-CoV-2 S1-specific IgG antibody concentrations by bead-based multiplex immunoassay (MIA) in binding antibody units per mL in the three groups at each timepoint. Horizontal dotted lines represent the cut-off for seropositivity (=10.08 BAU/mL). Horizontal lines represent the geometric mean + 95% CI of the geometric mean. d Per-participant factor changes for anti-S1-specific binding antibodies, calculated by dividing two responses. The dashed line indicates a factor change of 1 (no increase or decrease). Horizontal lines represent the geometric mean + 95% CI of the geometric mean. e SARS-CoV-2 anti-N-specific IgG antibody concentrations by bead-based immunoassay (MIA) in binding antibody units per mL in the three groups at each timepoint. Horizontal dotted lines represent the cut-off for seropositivity (=14.3 BAU/mL). Horizontal lines represent the geometric mean + 95% CI of the geometric mean. For the calculations of the GMFR D29/D01, D43/D01, and M07/D01, any antibody concentration for S1 and RBD at D01 reported below 1 was set to 1. For the calculation of the GMFR D43/D29, the antibody concentration for S1 for the non-responder in the ID-BM group at D29 was set to 1. Each symbol represents a sample from an individual participant. Black symbols in the IM group represent the two participants with SARS-CoV-2-spike-specific B-cells at baseline but no measurable anti-S or anti-N. ID intradermal, IM intramuscular, BM Bella-mu® needle, SN standard needle, LLoD lower limit of detection, IU/mL international units per mL, D day, M months.

Fig. 3. B-cell compartment and the immunogenicity of intradermal and intramuscular delivery of mRNA SARS-CoV-2 vaccine, according to the per-protocol analysis.

In total, 40 individuals were selected to investigate the B-cell response against the IM (100 µg) or ID (20 µg) standard delivery technique (ID-SN) of the SARS-CoV-2 vaccine. 12 individuals withdrew from the study and two individuals (IM and ID-SN group) were excluded at 7 months and were not shown due to a recent re-infection (PCR+). Vaccines were administered directly after sample collection at D01 and D29 (booster). The black data points represent the two individuals with the presence of SARS-CoV-2-specific B-cells at D01 prior to vaccination, which were excluded in the PP analysis. Including these participants in the ITT analysis did not change the outcome. a Percentages of B-cells specific for SARS-CoV-2-spike-protein, shown as frequencies from total B-cells per individual and vaccine delivery (IM, gray vs ID-SN, red). b The fold-change of the frequencies of SARS-CoV-2-spike-specific B-cells, 2 weeks after the second dose (D43/D29) and ~6 months after D43 (M07/D43). c Isotype usage of SARS-CoV-2-spike-specific B-cells as stacked bars at each timepoint for each vaccine delivery. d Correlation plot between IgG+ titers and IgG+ SARS-CoV-2-spike-specific B-cells. 95% CI is shown as an ellipse for each timepoint. Pearson correlation analysis results are depicted, and linear regression results are shown as a black line with shaded 95% CIs. Statistical analyses and Mann–Whitney U tests are performed to compare the vaccine deliveries (ID-SN and IM) for each timepoint. *=P < 0.05, **=P < 0.01. Individuals and median values are shown. ID intradermal, IM intramuscular, SN standard needle, CI confidence interval, D day, M month, PP per-protocol, ITT intention-to-treat.

Fig. 4. mRNA-1273 induced SARS-CoV-2-specific T-cell responses.

Spike-specific CD4⁺ and CD8⁺ T-cells were analyzed at D01, D29, D43 or M07. The second dose was given at the moment of D29. A pool of peptides derived from CMV, EBV, Flu and extra (CEFX) was used as a positive control and DMSO as a negative control. a Frequency of spike-specific CD4⁺ T-cells in time. Spike-specific CD4⁺ T-cells were defined as the frequency of CD154⁺ and/or CD137⁺ cells of total CD4⁺ T-cells, corrected for background in DMSO control. The dotted line represents the threshold for a response. b Frequency of individuals with a spike-specific CD4⁺ T-cell response above threshold. c Frequency of CEFX-specific CD4⁺ T-cells in time. d Frequency of spike-specific CD8⁺ T-cells in time. Spike-specific CD8⁺ T-cells were defined as the frequency CD69⁺ and/or CD137⁺ cells of total CD8⁺ T-cells, corrected for background in DMSO control. The dotted line represents the threshold for a response. e Frequency of individuals with a spike-specific CD8⁺ T-cell response above threshold. f Frequency of CEFX-specific CD8⁺ T-cells in time. Each point represents a single subject. Black symbols in the IM group represent the two participants with suspected previous SARS-CoV-2 infection based on SARS-CoV-2-spike-specific B-cells prior to vaccination. Mann–Whitney U tests were performed for statistical analysis. p-Values are categorized in the figures as: *p < 0.05; **p < 0.01 or ***p < 0.001. Categorized p-value was only shown if significant. The horizontal bold black line represents the median with 95% CI. The dotted line indicates the limit of quantification (LOQ). ID intradermal, IM intramuscular, D day, M months, SN standard needle, LLoD lower limit of detection, CI confidence interval.

Fig. 5. Adverse events related to vaccine administration in the ID-SN group and IM group, subdivided into mild, moderate, or severe.

All adverse events possibly, probably, or definitely related to the vaccination in the following 28 days after the first and second vaccine administration are reported. Grade 4 (potentially life-threatening) adverse events did not occur. Hyperpigmentation, itch, and dizziness are unsolicited adverse events. For a number of adverse events in the ID-BM group, see Supplementary Table 13. ID intradermal, IM intramuscular, BM Bella-mu® needle, SN standard needle.