Safety and immunogenicity of aerosolised Ad5-nCoV, intramuscular Ad5-nCoV, or inactivated COVID-19 vaccine CoronaVac given as the second booster following three doses of CoronaVac: a multicentre, open-label, phase 4, randomised trial

Abstract

Background: Aerosolised Ad5-nCoV is the first approved mucosal respiratory COVID-19 vaccine to be used as a booster after the primary immunisation with COVID-19 vaccines. This study aimed to evaluate the safety and immunogenicity of aerosolised Ad5-nCoV, intramuscular Ad5-nCoV, or inactivated COVID-19 vaccine CoronaVac given as the second booster.

Methods: This is an open-label, parallel-controlled, phase 4 randomised trial enrolling healthy adult participants (≥18 years) who had completed a two-dose primary immunisation and a booster immunisation with inactivated COVID-19 vaccines (CoronaVac only) at least 6 months before, in Lianshui and Donghai counties, Jiangsu Province, China. We recruited eligible participants from previous trials in China (NCT04892459, NCT04952727, and NCT05043259) as cohort 1 (with the serum before and after the first booster dose available), and from eligible volunteers in Lianshui and Donghai counties, Jiangsu Province, as cohort 2. Participants were randomly assigned at a ratio of 1:1:1, using a web-based interactive response randomisation system, to receive the fourth dose (second booster) of aerosolised Ad5-nCoV (0·1 mL of 1·0 × 10¹¹ viral particles per mL), intramuscular Ad5-nCoV (0·5 mL of 1·0 × 10¹¹ viral particles per mL), or inactivated COVID-19 vaccine CoronaVac (0·5 mL), respectively. The co-primary outcomes were safety and immunogenicity of geometric mean titres (GMTs) of serum neutralising antibodies against prototype live SARS-CoV-2 virus 28 days after the vaccination, assessed on a per-protocol basis. Non-inferiority or superiority was achieved when the lower limit of the 95% CI of the GMT ratio (heterologous group vs homologous group) exceeded 0·67 or 1·0, respectively. This study was registered with ClinicalTrials.gov, NCT05303584 and is ongoing.

Findings: Between April 23 and May 23, 2022, from 367 volunteers screened for eligibility, 356 participants met eligibility criteria and received a dose of aerosolised Ad5-nCoV (n=117), intramuscular Ad5-nCoV (n=120), or CoronaVac (n=119). Within 28 days of booster vaccination, participants in the intramuscular Ad5-nCoV group reported a significantly higher frequency of adverse reactions than those in the aerosolised Ad5-nCoV and intramuscular CoronaVac groups (30% vs 9% and 14%, respectively; p<0·0001). No serious adverse events related to the vaccination were reported. The heterologous boosting with aerosolised Ad5-nCoV triggered a GMT of 672·4 (95% CI 539·7-837·7) and intramuscular Ad5-nCoV triggered a serum neutralising antibody GMT of 582·6 (505·0-672·2) 28 days after the booster dose, both of which were significantly higher than the GMT in the CoronaVac group (58·5 [48·0-71·4]; p<0·0001).

Interpretation: A heterologous fourth dose (second booster) with either aerosolised Ad5-nCoV or intramuscular Ad5-nCoV was safe and highly immunogenic in healthy adults who had been immunised with three doses of CoronaVac.

Funding: National Natural Science Foundation of China, Jiangsu Provincial Science Fund for Distinguished Young Scholars, and Jiangsu Provincial Key Project of Science and Technology Plan.

Figure 1

Trial profile *Excluded due to severe hypertension (blood pressure of above 221/142 mm Hg), positive urinary pregnancy test, urticaria, psoriasis, or because they had undergone cholecystectomy within the past 14 days. The previous iSARS-CoV-2 infection status of participants was confirmed by asking the participants and by checking their recent medical visits.

Figure 2

Neutralising antibodies to wild-type SARS-CoV-2 and pseudovirus of omicron BA.4–5 before and after boosting GMT of neutralising antibodies to wild-type SARS-CoV-2 and pseudovirus of omicron BA.4–5 (A and C). GMFI of neutralising antibodies to wild-type SARS-CoV-2 and pseudovirus of omicron BA.4–5 (B and D). Error bars indicate 95% CIs. Each point on the graphs represents a sample. GMFI=geometric mean titre fold increase. GMT=geometric mean titre. ns=not significantly different. *p<0·01. †p<0·0001.

Figure 3

RBD-specific or N-specific IgG antibody titres before and after boosting GMT of anti-RBD IgG (A) and anti-N IgG (C). GMFI of anti-RBD IgG (B) and anti-N IgG (D). Error bars indicate 95% CIs. Each point on the graphs represents a sample. GMFI=geometric mean titre fold increase. GMT=geometric mean titre. RBD=receptor-binding domain. ns=not significantly different. *p<0·0001.

Figure 4

SARS-CoV-2 spike-specific T-cell cytokine responses before and after boosting IFN-γ (A), IL-2 (B), and TNF-α (C) cytokine concentrations. Data are the median (IQR) of positive spot counts per 10⁶ PBMCs and (n/N), where n indicates the number of negatives for T-cell responses of the participants, and N indicates the total number of participants. Each point on the graphs represents a sample. IFN-γ=interferon-γ. IL-2=interleukin-2. ns=not significantly different. TNF-α=tumour necrosis factor-α PBMCs=peripheral blood mononuclear cells. *p<0·01. †p<0·001.