Safety and immunogenicity of a reduced dose of the BNT162b2 mRNA COVID-19 vaccine (REDU-VAC): A single blind, randomized, non-inferiority trial

  1. Pieter Pannus
  2. Stéphanie Depickère
  3. Delphine Kemlin
  4. Sarah Houben
  5. Kristof Y. Neven
  6. Leo Heyndrickx
  7. Johan Michiels
  8. Elisabeth Willems
  9. Stéphane De Craeye
  10. Antoine Francotte
  11. Félicie Chaumont
  12. Véronique Olislagers
  13. Alexandra Waegemans
  14. Mathieu Verbrugghe
  15. Marie-Noëlle Schmickler
  16. Steven Van Gucht
  17. Katelijne Dierick
  18. Arnaud Marchant
  19. Isabelle Desombere
  20. Kevin K. Ariën
  21. Maria E. Goossens

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Abstract

Fractional dosing of COVID-19 vaccines could accelerate vaccination rates in low-income countries. Dose-finding studies of the mRNA vaccine BNT162b2 (Pfizer-BioNTech) suggest that a fractional dose induces comparable antibody responses to the full dose in people <55 years. Here, we report the safety and immunogenicity of a fractional dose regimen of the BNT162b2 vaccine. REDU-VAC is a participant-blinded, randomised, phase 4, non-inferiority study. Adults 18–55 years old, either previously infected or infection naïve, were randomly assigned to receive 20μg/20μg (fractional dose) or 30μg/30μg (full dose) of BNT162b2. The primary endpoint was the geometric mean ratio (GMR) of SARS-CoV-2 anti-RBD IgG titres at 28 days post second dose between the reduced and full dose regimens. The reduced dose was considered non-inferior to the full dose if the lower limit of the two-sided 95% CI of the GMR was >0.67. Primary analysis was done on the per-protocol population, including infection naïve participants only. 145 participants were enrolled and randomized, were mostly female (69.5%), of European origin (95%), with a mean age of 40.4 years (SD 7.9). At 28 days post second dose, the geometric mean titre (GMT) of anti-RBD IgG of the reduced dose regimen (1,705 BAU/mL) was not non-inferior to the full dose regimen (2,387 BAU/mL), with a GMR of 0.714 (two-sided 95% CI 0.540–0.944). No serious adverse events occurred. While non-inferiority of the reduced dose regimen was not demonstrated, the anti-RBD IgG titre was only moderately lower than that of the full dose regimen and, importantly, still markedly higher than the reported antibody response to the licensed adenoviral vector vaccines. These data suggest that reduced doses of the BNT162b2 mRNA vaccine may offer additional benefit as compared to the vaccines currently in use in most low and middle-income countries, warranting larger immunogenicity and effectiveness trials.

Trial Registration: The trial is registered at ClinicalTrials.gov ( NCT04852861 ).

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  1. Version published to 10.1371/journal.pgph.0001308
  2. ScreenIT

    SciScore for 10.1101/2022.03.25.22272599: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: The trial was reviewed and approved by the Erasme Hospital Ethics Committee (P2021/251) and the Federal Agency for Medicines and Health Products (EudraCT: 2021-002088-23A).
    Consent: At the baseline visit, participants provided informed consent before having blood drawn and being vaccinated.
    Sex as a biological variablenot detected.
    RandomizationStudy design: REDU-VAC is a participant-blinded, randomised, phase 4, multicentre, non-inferiority study investigating safety, reactogenicity and immunogenicity of a fractional dose of the mRNA COVID-19 vaccine BNT162b2 (Pfizer-BioNTech).
    BlindingTo ensure participant blinding to the vaccine dose, randomisation lists were kept out of sight, vaccines were prepared, and syringes were filled beforehand.
    Power AnalysisStatistical analysis: The sample size was calculated assuming a true difference of geometric means of the primary outcome on the log10 scale being 0 between the reduced and the full dose, and a standard deviation of GMT on the log10 scale being 0.27 (17).
    Cell Line Authenticationnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    SARS-CoV-2 anti-receptor binding domain (RBD) specific IgG concentrations were measured by ELISA (reported as Binding Antibody Units [BAU]/mL) on days 0/21/49 and month 6.
    SARS-CoV-2 anti-receptor binding domain (RBD
    suggested: None
    SARS-CoV-2 Specific Binding Antibodies: Enzyme-linked immunosorbent assay: Binding antibodies at baseline and after vaccination were assessed using an enzyme-linked immunosorbent assay (ELISA) for the quantitative detection of IgG-class antibodies to RBD (Receptor Binding Domain, Wuhan strain) (Wantai SARS-CoV-2 IgG ELISA (Quantitative); CE-marked; WS-1396; Beijing Wantai Biological Pharmacy Enterprise Co., Ltd, China).
    IgG-class
    suggested: None
    Next, plates were incubated (37°C, 30 min) with horseradish peroxidase (HRP)-conjugated anti-human IgG antibodies and washed five times before adding a TMB and urea peroxide solution for 15 min (37°C, dark).
    anti-human IgG
    suggested: None
    Multiplex Immunoassay (Luminex): Antibody responses at baseline were tested with an in house multiplex immunoassay (MIA).
    MIA
    suggested: None
    In this test, IgG antibodies to SARS-CoV-2 antigens RBD, S1, S2 and N (Wuhan strain) were measured simultaneously in one assay run.
    IgG
    suggested: None
    SARS-CoV-2
    suggested: None
    SARS-CoV-2 Neutralizing Antibodies: Serial dilutions of heat-inactivated serum (1/50-1/25600 in EMEM supplemented with 2mM L-glutamine, 100U/ml - 100μg/ml of Penicillin-Streptomycin and 2% fetal bovine serum) were incubated during 1h (37°C, 7% CO2) with 3xTCID100 of a wild type Wuhan strain (2019-nCoV-Italy-INMI1, reference 008V-03893), the B.1.617.2 Delta variant (83DJ-1) and the BA.1 Omicron variant of SARS-CoV-2, in parallel.
    83DJ-1
    suggested: None
    Plates were then coated with human IFN-γ antibody (15 µg/ml) overnight at 4°C, washed and blocked with 200µl of Roswell Park Memorial Institute (RPMI) containing 10% fetal bovine serum (FBS) for at least two hours.
    IFN-γ
    suggested: (MABTECH Cat# 3420-2APT, RRID:AB_2877719)
    After incubation, the plates were washed and incubated with the human biotinylated IFN-γ detection antibody (1µg/ml) for 2 hours, washed and the streptavidin–Horseradish Peroxidase (streptavidin-HRP) diluted at 1/750 in PBS-0,5% FBS was added for one hour.
    streptavidin-HRP
    suggested: (Cell Signaling Technology Cat# 3999, RRID:AB_10830897)
    Flow cytometry: Cells were stimulated in 96-well round-bottom plates with 1 × 106 PBMCs in RPMI 1640 medium (Lonza, Basel, Switzerland) supplemented with 10% heat-inactivated FBS (Sigma-Aldrich, Kawasaki, Japan), penicillin/streptomycin, amino acids and PepMix SARS-CoV-2 spike glycoprotein peptide pools (SUB1-SUB2, JPT, Berlin, Germany) in the presence of 1µg/mL purified anti-CD28 antibody (clone CD28.2, BD Biosciences, New Jersey, USA).
    anti-CD28
    suggested: None
    After stimulation, Live/Dead fixable red stain (ThermoFisher, Massachusetts, USA) was used to exclude dead cells and the staining of surface antigens was carried out for 20 min with the following fluorochrome-conjugated antibodies: CD3 BV711 (UCHT-1; BD), anti-CD8 PeCy7 (RPA-T8; BD), CD4 HV450 (RPA-T4; BD).
    CD3
    suggested: None
    anti-CD8
    suggested: None
    CD4
    suggested: None
    Experimental Models: Cell Lines
    SentencesResources
    Sample-virus mixtures and virus/cell controls were added to Vero cells (18.000 cells/well) in a 96-well plate and incubated for five days (37°C, 7% CO2).
    Vero
    suggested: None
    Software and Algorithms
    SentencesResources
    Net OD values were converted to arbitrary IgG units per ml by interpolation from a point-by-point plot fitted with the standard concentrations and net OD values (correlation coefficient R2≥0.9801), using GraphPad Prism version 9.0.0 for Windows (GraphPad Software, San Diego, California USA) and exported to Microsoft Excel.
    GraphPad Prism
    suggested: (GraphPad Prism, RRID:SCR_002798)
    GraphPad
    suggested: (GraphPad Prism, RRID:SCR_002798)
    Microsoft Excel
    suggested: (Microsoft Excel, RRID:SCR_016137)
    Samples were acquired on a BD LSRFortessa flow cytometer and analyzed with FlowJo v9.
    FlowJo
    suggested: (FlowJo, RRID:SCR_008520)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    This study has several limitations, the first being the relatively limited sample size. A larger number of participants would have resulted in smaller confidence intervals around the GMRs, which might have impacted the conclusions on non-inferiority. Although males were underrepresented in this study, we do not believe this is a major limitation as immune responses to COVID-19 mRNA vaccination in healthy, younger subjects are only minimally gender-dependent and importantly, there is no basis to assume that fractional dosing would affect immune responses differently between males and females (24–26). Secondly, the small proportion of previously infected participants in our study population (17/144, 12%) does not allow for a separate sensitivity analysis in this group. With record high COVID-19 incidences worldwide, the proportion of the population who experienced a past infection is rapidly growing, making analyses including previously infected people ever more relevant. In addition, breakthrough infections were not actively monitored by regular molecular testing. Therefore, we may have missed asymptomatic infections, which are not reported by the study participants. Thirdly, while protection from infection or disease has been convincingly correlated with titres of binding and neutralizing antibodies, as discussed previously, it is not possible to determine with certainty that the moderately lower titres observed in our study will translate to equally moderately lower efficacy...

    Results from TrialIdentifier: We found the following clinical trial numbers in your paper:

    IdentifierStatusTitle
    NCT04852861Enrolling by invitationCOVID-19: Safety and Immunogenicity of a Reduced Dose of the…

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a protocol registration statement.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  3. Version published to 10.1101/2022.03.25.22272599v1 on medRxiv