Study participants
Between January 14 and March 10, a total of 1006 healthcare workers in Shanghai Ruijin Hospital were enrolled in this study. The baseline characteristics of the participants are shown in Table 1. Of them, 284 were male and 722 were female, the mean age was 35.89 years. 169 (16.80%) participants have at least one underlying disease.
Safety outcomes
No serious adverse events were noted. 447 (44.43%) of 1006 vaccine recipients had at least one adverse reaction after either vaccination. The common adverse reactions were reported more often after the administration of the second dose (Table 2). The overall incidence of adverse reactions was 308 (30.62%) of 1006 vaccine recipients after the second dose, compared with 241 (23.96%) after the first dose.
At least one local adverse reaction occurred after either vaccination in 258 (25.65%) of 1006 vaccine recipients. The proportion of vaccine recipients reporting local adverse reactions increased after the second dose. Pain at the injection-site was the most frequent solicited local adverse reaction, which was reported by 231 (22.96%) participants, and was reported more frequently among vaccine recipients after the second dose (160 [15.91%]) than among vaccine recipients after the first dose (97 [9.64%]). The additional injection site adverse reaction included redness (65 [6.46%]), swelling (50 [4.97%]), and rash (15 [1.49%]).
At least one systematic adverse reaction was reported by 310 (30.82%) of 1006 vaccine recipients after either vaccination, and the most common systematic adverse reaction was fatigue, which was reported in 206 (20.48%) vaccine recipients. The additional systemic adverse reactions followed by were headache (101 [10.04%]), diarrhea (34 [3.38%]), nausea and vomiting (31 [3.08%]), fever (27 [2.68%]), mucocutaneous abnormality (22 [2.19%]), myalgia and arthralgia (18 [1.79%]).
Clinical laboratory values revealed few mild to moderate transient abnormalities. After the first dose vaccination, 39 vaccine recipients had decreased hemoglobin, 51 had increased white blood cell count, two had increased lymphocyte count, 14 had increased neutrophils count, 31 had increased alanine aminotransferase, 49 had increased aspartate aminotransferase, 14 had increased serum total bilirubin, 40 had increased blood urea nitrogen, and two had increased creatinine. After the second dose vaccination, 27 vaccine recipients had decreased hemoglobin, 46 had increased white blood cell count, four had increased lymphocyte count, 15 had increased neutrophils count, 30 had increased alanine aminotransferase, 35 had increased aspartate aminotransferase, two had increased serum total bilirubin, 27 had increased blood urea nitrogen, and four had increased creatinine. No instances were considered as clinically significant.
Immunogenicity response
Immunological analyses were done among individuals who had sufficient blood samples. On the day of the first dose, none of the participants had any detectable specific antibodies against SARS-CoV-2 or neutralizing antibodies to the pseudoviruses. Rapid antibody responses to SARS-CoV-2 were observed in 609 (63.17%) of 964 individuals who were collected sufficient blood samples for immunological analyses on day 21 after the first dose (Figure 1), and the median antibody level was 5.32 (2.32-13.35).
An unbiased set of post-immunization sera of 760 individuals were tested for neutralizing antibodies by day 28 after the whole-course vaccination. The seroconversion rate of neutralizing antibodies was 698 (91.84%) of 760 individuals, and the GMT was 62.68 (95% CI 57.02-68.91). The specific antibodies against SARS-CoV-2 were detected in 731 (96.18%) of 760 vaccine recipients, and the median antibody level was 33.96 (12.56-82.04). Sex was not a factor that affect the induction of neutralizing antibody. Vaccine recipients with subsequent seroconversion of neutralizing antibodies had significant younger age than those who did not achieve seroconversion of neutralizing antibodies (36.74 [9.92] vs. 40.50 [8.95], p < 0.010).
In 470 selected participants with positive neutralizing activity against the Wuhan reference strain (GMT 68.72, [95% CI 61.97-76.20]), neutralization assays were also performed against multiple SARS-CoV-2 variants. As shown in Figure 2, 57 (12.13%) vaccine-elicited sera showed complete or partial loss of neutralizing activity against lineage B.1.1.7, and the GMTs against B.1.1.7 declined 2.2-fold to 31.17 (95% CI 27.71-35.07) compared to their titres against wild-type strains. 99 (20.97%) and 114 (24.26%) vaccine-elicited sera showed complete or partial loss of neutralizing activity against lineage B.1.526 and lineage P.1, respectively. The GMTs against lineage P.1 declined 1.9-fold to 37.07 (95% CI 27.71-35.07), whereas a marked decrease by 3.8-fold was observed in GMTs against lineage B.1.526 (18.21 [95% CI 16.40-20.23]). Only 199 (42.34%) vaccine-elicited sera preserved neutralizing activity against lineage B.1.351, with significantly reduced GMTs (15.08, [95% CI 13.06-17.42]) compared with their titres against wild-type strains.
We further analyzed the consistency of seroconversion of the neutralizing antibody among these variants. Only 14 vaccine-elicited sera did not induce neutralizing antibodies to any of the mutant strains. Among 199 vaccine-elicited sera that were seropositive against lineage B.1.351, only one had negative neutralizing activity against the rest three variants. We than analyzed the neutralizing activity against the three variants including B.1.1.7, B.1.526, and P.1 with less resistance, 285 (60.64%) vaccine-elicited sera preserved neutralizing activity against all three variants, and 354 (75.32%) vaccine-elicited sera preserved neutralizing activity against any two variants.
Cytokine responses
The dynamic changes of several key inflammatory cytokines, including interferon-γ (IFN-γ), interleukin-10 (IL-10), IL-12p70, IL-13, IL-2, IL-6, IL-8, and tumor necrosis factor-α (TNF-α), were chosen to be tested in serum at different time points. The levels of certain cytokines showed notable changes from the first dose through 28 days after the second dose (Figure 3). On 21 days post the first dose and on 28 days post the second dose, significant increases were observed in the levels of IFN-γ, IL-10, and IL-13 when compared with their levels on the day of the first dose. The levels of IL-8 and TNF-α showed significant increases on 21 days post the first dose, and then had significant decreases on 28 days post the second dose.
The cytokine response was lower among participants who did not successfully induce neutralizing antibody against SARS-CoV-2, including the levels of IFN-γ and TNF-α at 28 days post the whole-course vaccination, and the level of IL-12p70 on the day of the first dose (Figure 4).