Safety and immunogenicity of a recombinant tandem-repeat dimeric RBD protein vaccine against COVID-19 in adults: pooled analysis of two randomized, double-blind, placebo-controlled, phase 1 and 2 trials

  1. Shilong Yang
  2. Yan Li
  3. Lianpan Dai
  4. Jianfeng Wang
  5. Peng He
  6. Changgui Li
  7. Xin Fang
  8. Chenfei Wang
  9. Xiang Zhao
  10. Enqi Huang
  11. Changwei Wu
  12. Zaixin Zhong
  13. Fengze Wang
  14. Xiaomin Duan
  15. Siyu Tian
  16. Lili Wu
  17. Yan Liu
  18. Yi Luo
  19. Zhihai Chen
  20. Fangjun Li
  21. Junhua Li
  22. Xian Yu
  23. Hong Ren
  24. Lihong Liu
  25. Shufang Meng
  26. Jinghua Yan
  27. Zhongyu Hu
  28. Lidong Gao
  29. George F. Gao

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Abstract

Background

A safe and effective coronavirus disease 2019 (COVID-19) vaccine is urgently needed to control the ongoing pandemic. Although progress has been made recently with several candidates reporting positive efficacy results, COVID-19 vaccines developed so far cannot meet the global vaccine demand. We developed a protein subunit vaccine against COVID-19, using dimeric form of receptor-binding domain (RBD) as the antigen. We aimed to assess the safety and immunogenicity of this vaccine in humans and determine the appropriate dose and schedule for an efficacy study.

Methods

We did two randomized, double-blind, placebo-controlled, phase 1 and 2 trials for an RBD-based protein subunit vaccine, ZF2001. In phase 1 study, 50 healthy adults aged 18-59 years were enrolled and randomly allocated to three groups to receive three doses of vaccine (25 μg or 50 μg RBD-dimer, with adjuvant) or placebo (adjuvant-only) intramuscularly, 30 days apart. In phase 2 study, 900 healthy adults aged 18-59 years were enrolled and randomly allocated to six groups to receive vaccine (25 μg or 50 μg RBD-dimer, with adjuvant) or placebo (adjuvant-only) intramuscularly, with the former 3 groups given two doses and the latter 3 groups given three doses, 30 days apart. For phase 1 trial, the primary outcome was safety, as measured by the occurrence of adverse events and serious adverse events. The secondary outcome was immunogenicity as measured by the seroconversion rate and magnitude of antigen-binding antibodies, neutralizing antibodies and T-cell cytokine production. For phase 2 trial, the primary outcome included both safety and immunogenicity. These trials are registered with ClinicaTrials.gov, NCT04445194 and NCT04466085 .

Findings

Between June 22 and September 15, 2020, 50 participants were enrolled to the phase 1 study (mean age 32.6 years) and 900 participants were enrolled to phase 2 study (mean age 43.5 years), to receive vaccine or placebo with a two-dose or three-dose schedule. For both trials, local and systemic adverse reactions were absent or mild in most participants. There were no serious adverse events related to vaccine in either trial. After three doses, neutralizing antibodies were detected in all participants receiving either 25 μg or 50 μg dose of vaccine in phase 1 study, and in 97% (the 25 μg group) and 93% (the 50 μg group) of participants, respectively, in phase 2 study. The SARS-CoV-2-neutralizing geometric mean titres (GMTs) were 94.5 for the 25 μg group and 117.8 for the 50 μg group in phase 1, and 102.5 for the 25 μg group and 69.1 for the 50 μg group in phase 2, exceeding the level of a panel of COVID-19 convalescent samples (GMT, 51). Vaccine induced balanced T H 1 and T H 2 responses. The 50 μg group did not show enhanced immunogenicity compared with the 25 μg group.

Interpretation

The protein subunit vaccine ZF2001 is well-tolerated and immunogenic. The safety and immunogenicity data from phase 1 and 2 trials for ZF2001 support the use of 25 μg vaccine dose with three-dose schedule to an ongoing phase 3 large-scale evaluation for safety and efficacy.

Funding

National Program on Key Research Project of China, National Science and Technology Major Projects of Drug Discovery, Strategic Priority Research Program of the Chinese Academy of Sciences, and Anhui Zhifei Longcom Biopharmaceutical.

Article activity feed

  1. ScreenIT

    SciScore for 10.1101/2020.12.20.20248602: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementConsent: All participants provided written informed consent before enrollment in the trial.
    IRB: The trial protocol was approved by the institutional review board of The Second Affiliated Hospital of Chongqing Medical University, Beijing Chao-Yang Hospital of Capital Medical University, Hunan Provincial Center for Disease Control, Prevention and National Medical Products Administration (NMPA), China and was performed in accordance with the Declaration of Helsinki and Good Clinical Practice.
    RandomizationThe trial was designed with double-blind, randomized and placebo-parallel-controlled.
    BlindingThese randomisation statisticians were not allowed to participate in other related work of these clinical trials and not allowed to disclose the blind code to any personnel participating in this clinical trial.
    Power AnalysisStatistical analysis: Based on clinical consideration and recommendation of pilot trial and technical guideline issued by the NMPA in China, the sample sizes for two trials were practical, and were not determined on a formal statistical power calculation.
    Sex as a biological variableEligible participants were healthy men and nonpregnant women, 18 to 59 years of age.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    Randomisation and masking: The randomisation statisticians used SAS statistical software (version 9.4) to generate the random table of participants in each dose group.
    SAS
    suggested: (SASqPCR, RRID:SCR_003056)
    Statistical analyses were using SAS (version 9.4) and GraphPad Prism (version 8.0.1).
    GraphPad Prism
    suggested: (GraphPad Prism, RRID:SCR_002798)

    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 trial report has several limitations. First, the participants in both trials were young adults aged from 18-59, not including juvenile and elderly persons, whereas, the elderly is more vulnerable to SARS-CoV-2. Moreover, the participants had limited ethnic diversity, mainly the ethnic Han. These limitations will be addressed by our outreach study for cohort covering broader age range and ethnic backgrounds. Second, the immunogenicity was tested at day 30 post full vaccination in phase 1 and day 14 post full vaccination in phase 2, which cannot be assessed for the duration of the immune response. Immune responses at later timepoints including those at least 6 months post vaccination will be obtained in the follow-up visits and investigation. Third, there was still no benchmark to evaluate protective immune responses against COVID-19. Therefore, although ZF2001 induced neutralizing GMTs higher than the convalescent samples, it is yet hard to predict its protective efficacy. Since no participant had SARS-CoV-2 exposure, we were unable to assess the protective efficacy and vaccine-associated enhanced diseases at this moment. This limitation will be addressed in the ongoing international multi-center phase 3 trials.

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

    IdentifierStatusTitle
    NCT04445194Active, not recruitingPhase I Clinical Study of Recombinant Novel Coronavirus Vacc…
    NCT04466085Active, not recruitingClinical Study of Recombinant Novel Coronavirus Vaccine
    NCT04646590RecruitingA Phase III Clinical Trial to Determine the Safety and Effic…

    Results from Barzooka: We found bar graphs of continuous data. We recommend replacing bar graphs with more informative graphics, as many different datasets can lead to the same bar graph. The actual data may suggest different conclusions from the summary statistics. For more information, please see Weissgerber et al (2015).

    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.
    • No protocol registration statement was detected.

    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.

  2. NCRC

    Our take

    This study, available as a preprint and thus not yet peer reviewed, includes both phase 1 and phase 2 clinical trial data demonstrating the safety and immunogenicity of ZF2001, a vaccine manufactured by Anhui Zhifei Longcom Biopharmaceutical. This is the first clinical data reported for an RBD-based protein subunit vaccine for COVID-19. The vaccine was well tolerated and immunogenic. The data strongly support continued studies in phase 3 trials. Phase 3 trials are ongoing with a 25 ug, 3-dose regimen.

    Study design

    randomized-controlled-trial

    Study population and setting

    Reported are results from phase 1 and phase 2 clinical trials of a SARS-CoV-2 S protein receptor-binding domain (RBD)-based protein subunit vaccine against COVID-19, ZF2001, manufactured by Anhui Zhifei Longcom Biopharmaceutical. Both trials were randomized, double-blinded, and placebo-controlled. The phase 1 study enrolled 50 healthy adults, aged 18-59 into one of three groups: 25 ug vaccine, 50 ug vaccine, or placebo. All groups were administered 3 doses 30 days apart. The primary endpoint was safety, with the secondary endpoint of immunogenicity. Phase 2 studies enrolled 900 participants and included six groups, with three groups receiving 3 doses of either 25 ug vaccine, 50 ug vaccine, or placebo, and 3 groups receiving 2 doses of either 25 ug vaccine, 50 ug vaccine, or placebo. Primary endpoints were safety and immunogenicity. In both studies, samples were taken at determined intervals to assess immunogenicity. Both trials were conducted in China, with phase 1 in Chongqing and Beijing, and Phase 2 in Xiangtan.

    Summary of main findings

    All vaccine regimens were well tolerated. Local adverse events included pain, swelling, induration, redness, rash and pruritus. Systemic adverse events included fever, cough, dyspnea, diarrhea, anorexia, nausea, vomiting, muscle pain other than the injection site, arthritis, joint pain, headache, fatigue, acute allergic reaction, irritation or inhibition, and mental disorder. No vaccine-related serious adverse events were reported. In the phase 1 study, 61% (25 ug group) and 79% (50 ug group) of participants had seroconverted by day 30 post-first dose and 100% of both groups had seroconverted by day 30 post-second dose. In the phase 2 study, 59-65% seroconverted by day 30 post-first vaccination, 94%-97% at 30 days post-second vaccination, and 97%-99% at 14 days post-third dose. However, for all vaccine groups in both phase 1 and phase 2 studies, neutralizing titers were only similar to or better than convalescent patient serum at time points following the third dose. There was no significant enhancement of neutralizing titers in the 50 ug groups compared to the 25 ug groups. T-cell responses were also observed in all vaccine groups with no significant difference between groups. Maximal responses first observed at 30 days post-second dose.

    Study strengths

    Demonstration of neutralizing antibodies titers elicited by this vaccine equal to or greater than convalescent plasma is positive. While a correlate of protection has not been determined for SARS-CoV-2, to date, vaccines that have been issued an emergency use authorization (EUA) have demonstrated neutralizing titers similar to or better than convalescent plasma.

    Limitations

    While demonstrating that ZF2001 can elicit a T-cell response is positive, it is not clear what type or level of response is needed to confer protection against disease. This study did not include elderly populations and has very limited population diversity. Also, duration of the immune response is not tested past 30 days post-third dose. These limitations will be addressed in the ongoing phase 3 trial. The data indicate that the immune response is greatly boosted with the 3rd vaccination, thus a 25 ug, 3-dose regimen will be used in the phase 3 trial. A 3-dose vaccine regime could prove to be logistically difficult in some areas and compliance may be lower than the current 2-dose regimens for other vaccines already in use under EUA.

    Value added

    This is the first clinical data reported for an RBD-based protein subunit vaccine for COVID-19. The vaccine was well tolerated and immunogenic. The data strongly support continued studies in phase 3 trials.

  3. Version published to 10.1101/2020.12.20.20248602v1 on medRxiv