Safety and immunogenicity of heterologous boost immunization with an adenovirus type-5-vectored and protein-subunit-based COVID-19 vaccine (Convidecia/ZF2001): A randomized, observer-blinded, placebo-controlled trial

Abstract

Background: Heterologous boost vaccination has been proposed as an option to elicit stronger and broader, or longer-lasting immunity. We assessed the safety and immunogenicity of heterologous immunization with a recombinant adenovirus type-5-vectored Coronavirus Disease 2019 (COVID-19) vaccine (Convidecia, hereafter referred to as CV) and a protein-subunit-based COVID-19 vaccine (ZF2001, hereafter referred to as ZF).

Methods and findings: We conducted a randomized, observer-blinded, placebo-controlled trial, in which healthy adults aged 18 years or older, who have received 1 dose of Convidecia, with no history of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, were recruited in Jiangsu, China. Sixty participants were randomly assigned (2:1) to receive either 1 dose of ZF2001 or placebo control (trivalent inactivated influenza vaccine (TIV)) administered at 28 days after priming, and received the third injection with ZF2001 at 5 months, referred to as CV/ZF/ZF (D0-D28-M5) and CV/ZF (D0-M5) regimen, respectively. Sixty participants were randomly assigned (2:1) to receive either 1 dose of ZF2001 or TIV administered at 56 days after priming, and received the third injection with ZF2001 at 6 months, referred to as CV/ZF/ZF (D0-D56-M6) and CV/ZF (D0-M6) regimen, respectively. Participants and investigators were masked to the vaccine received but not to the boosting interval. Primary endpoints were the geometric mean titer (GMT) of neutralizing antibodies against wild-type SARS-CoV-2 and 7-day solicited adverse reactions. The primary analysis was done in the intention-to-treat population. Between April 7, 2021 and May 6, 2021, 120 eligible participants were randomly assigned to receive ZF2001/ZF2001 (n = 40) or TIV/ZF2001 (n = 20) 28 days and 5 months post priming, and receive ZF2001/ZF2001 (n = 40) or TIV/ZF2001 (n = 20) 56 days and 6 months post priming. Of them, 7 participants did not receive the third injection with ZF2001. A total of 26 participants (21.7%) reported solicited adverse reactions within 7 days post boost vaccinations, and all the reported adverse reactions were mild, with 13 (32.5%) in CV/ZF/ZF (D0-D28-M5) regimen, 7 (35.0%) in CV/ZF (D0- M5) regimen, 4 (10.0%) in CV/ZF/ZF (D0-D56-M6) regimen, and 2 (10.0%) in CV/ZF (D0-M6) regimen, respectively. At 14 days post first boost, GMTs of neutralizing antibodies in recipients receiving ZF2001 at 28 days and 56 days post priming were 18.7 (95% CI 13.7 to 25.5) and 25.9 (17.0 to 39.3), respectively, with geometric mean ratios of 2.0 (1.2 to 3.5) and 3.4 (1.8 to 6.4) compared to TIV. GMTs at 14 days after second boost of neutralizing antibodies increased to 107.2 (73.7 to 155.8) in CV/ZF/ZF (D0-D28-M5) regimen and 141.2 (83.4 to 238.8) in CV/ZF/ZF (D0-D56-M6) regimen. Two-dose schedules of CV/ZF (D0-M5) and CV/ZF (D0-M6) induced antibody levels comparable with that elicited by 3-dose schedules, with GMTs of 90.5 (45.6, 179.8) and 94.1 (44.0, 200.9), respectively. Study limitations include the absence of vaccine effectiveness in a real-world setting and current lack of immune persistence data.

Conclusions: Heterologous boosting with ZF2001 following primary vaccination with Convidecia is more immunogenic than a single dose of Convidecia and is not associated with safety concerns. These results support flexibility in cooperating viral vectored and recombinant protein vaccines.

Trial registration: Study on Heterologous Prime-boost of Recombinant COVID-19 Vaccine (Ad5 Vector) and RBD-based Protein Subunit Vaccine; ClinicalTrial.gov NCT04833101.

Conflict of interest statement

I have read the journal’s policy and the authors of this manuscript have the following competing interests: JL reports grants from National Natural Science Foundation of China (grant number 82173584). FZ reports grants from Jiangsu Provincial Key Research and Development Program (grant number BE2021738). LD is an inventor of the patent for the protein subunit vaccine ZF2001. WC, YZ and CC are the employees of Anhui Zhifei Longcom Biopharmaceutical. All other authors declare no competing interest.

Figures

Fig 1. Study design and trial profile.

(A) Immunization schedule and serum collection in 4 prime-boost regimens. CV/ZF/ZF (D0-D28-M5) refers to receiving Convidecia/ZF2001/ZF2001 at day 0, day 28, and month 5 (day 150); CV/ZF (D0-M5) refers to receiving Convidecia/TIV/ZF2001 at day 0, day 28, and month 5 (day 150); CV/ZF/ZF (D0-D56-M6) refers to receiving Convidecia/ZF2001/ZF2001 at day 0, day 56, and month 6 (day 180); and CV/ZF (D0-M6) refers to receiving Convidecia/TIV/ZF2001 at day 0, day 56, and month 6 (day 180). For CV/ZF/ZF (D0-D28-M5) and CV/ZF (D0-M5) regimen, blood samples were collected at day 28 (28 days post priming, before first boost), day 42 (14 days post first boost), day 56 (28 days post first boost), and day 164 (14 days post second boost). For CV/ZF/ZF (D0-D56-M6) and CV/ZF (D0-M6) regimen, blood samples were collected at day 28 (28 days post priming), day 56 (before first boost), day 70 (14 days post first boost), day 84 (28 days post first boost), and day 184 (14 days post second boost). (B) Trial profile. Seven participants discontinued follow up after vaccination. The reasons for dropout are withdrawn consents for participation. TIV, trivalent inactivated influenza vaccine.

Fig 2. Neutralizing antibodies against wild-type SARS-CoV-2 after prime and boost dose.

(A and B) GMTs of neutralizing antibodies to wild-type SARS-CoV-2 28 days after prime dose, 14 days after first and second boost dose (C) GMFI of neutralizing antibodies to wild-type SARS-CoV-2 14 days after first and second boost, compared to baseline (28 days post prime). (D) Seroconversion rate (%) of neutralizing antibodies to wild-type SARS-CoV-2 14 days after first and second boost. Seroconversion was defined as at least a 4-fold increase in the antibody titers at different time points after boost compared to baseline (28 days post prime). The WHO reference (1,000 IU/ ml) is equivalent to a neutralizing antibody titer of 1:320 against wild-type SARS-CoV-2. Cutoff (1:8) refers to the detection limit. Up arrow represents the boost immunization. Horizontal bars show geometric mean or mean and error bars show 95% CI. **P < 0.05, ****P < 0.001. CV/ZF/ZF (D0-D28-M5) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 28, and month 5; CV/ZF (D0-M5) = receiving Convidecia/ZF2001 at day 0 and month 5; CV/ZF/ZF (D0-D56-M6) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 56, and month 6; CV/ZF (D0-M6) = receiving Convidecia/ZF2001 at day 0 and month 6. CI, confidence interval; GMFI, geometric mean fold increase; GMT, geometric mean titer; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2; WHO, World Health Organization.

Fig 3. Neutralizing antibodies to wild-type SARS-CoV-2 after prime and boost dose according to age.

Data presented are neutralizing antibodies to wild-type SARS-CoV-2 28 days after prime dose, 14 days after first and second boost according to age (18–59 years and ≥60 years) in each regimen. Cutoff (1:8) refers to the detection limit. Horizontal bars show geometric mean titer and error bars show 95% CI. Up arrow represents the boost immunization. CV/ZF/ZF (D0-D28-M5) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 28, and month 5; CV/ZF (D0-M5) = receiving Convidecia/ZF2001 at day 0 and month 5; CV/ZF/ZF (D0-D56-M6) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 56, and month 6; CV/ZF (D0-M6) = receiving Convidecia/ZF2001 at day 0 and month 6. CI, confidence interval; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2.

Fig 4. SARS-CoV-2-specific IgG antibodies after prime and boost dose.

(A and B) GMTs of anti-RBD IgG (A and B) and anti-spike IgG (C and D) 28 days after prime dose, 14 days after first and second boost dose. Horizontal bars show geometric mean concentration and error bars show 95% CI. Up arrow represents the boost immunization. ****P < 0.001. RBD = SARS-CoV-2 receptor-binding domain. IU/ml = International units per milliliter. CV/ZF/ZF (D0-D28-M5) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 28, and month 5; CV/ZF (D0-M5) = receiving Convidecia/ZF2001 at day 0 and month 5; CV/ZF/ZF (D0-D56-M6) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 56, and month 6; CV/ZF (D0-M6) = receiving Convidecia/ZF2001 at day 0 and month 6. CI, confidence interval; IgG, immunoglobulin G; RBD, receptor-binding domain; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2.

Fig 5. Neutralizing antibodies against the Delta variant and specific T-cell responses after prime and boost dose.

(A and B) Geometric mean ratios of neutralizing antibodies against wild-type relative to Delta 28 days post prime dose (A), and 14 days post second boost dose (B). (C) GMTs of neutralizing antibodies to the Delta variant 28 days post prime dose and 14 days post second boost dose. (D) Spot-forming cells with secretion of IFN-γ cytokines per 1 × 106 PBMCs measured by ELISpot 28 days post prime dose, and 14 days post first and second boost dose. The numbers indicate the geometric mean ratios. Cutoff (1:4) refers to the detection limit. Horizontal bars show geometric mean titer (C) and median (D). Error bars show 95% CI in panel (C), and interquartile range in panel (D). CV/ZF/ZF (D0-D28-M5) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 28, and month 5; CV/ZF (D0-M5) = receiving Convidecia/ZF2001 at day 0 and month 5; CV/ZF/ZF (D0-D56-M6) = receiving Convidecia/ZF2001/ZF2001 at day 0, day 56, and month 6; CV/ZF (D0-M6) = receiving Convidecia/ZF2001 at day 0 and month 6. CI, confidence interval; ELISpot, enzyme-linked immunospot; GMT, geometric mean titer; IFN, interferon; PBMC, peripheral blood mononuclear cell.