The comparison of Immune response to Third booster dose with of ChAdOx-1 or BNT162b2 COVID-19 vaccine in healthcare workers after receiving two doses of CoronaVac

doi:10.21203/rs.3.rs-5320238/v1

Background

The COVID-19 outbreak has significantly impacted public health, with vaccine effectiveness being crucial for control. The efficacy of heterologous prime-boost vaccines remains unclear. This study compared AZD1222 and BNT162b2 as booster doses given 90 days after two CoronaVac doses.

Methods

Participants who received two CoronaVac doses at least 90 days earlier chose either the AZD1222 or BNT162b2 booster based on individual preference. Anti-Spike receptor-binding domain (anti-S-RBD) IgG levels were measured on days 14, 28, and 90, and surrogate virus neutralization tests (sVNT) were conducted on days 14 and 90.

Results

A total of 100 subjects participated in the study: 36 males and 64 females. The mean age in the AZD1222 group was 42.82±6.01 years, and in the BNT162b2 group, it was 37.3±8.07 years (p-value <0.05). The mean interval between the previous vaccine dose and the booster dose was 87.3±20.1 days in the AZD1222 group and 109.2±17.6 days in the BNT162b2 group (p-value <0.05). Anti-S-RBD levels in the BNT162b2 group were significantly higher than those in the AZD1222 group on days 14, 28, and 90. The sVNT inhibition of the Delta variant spike protein was also significantly higher in the BNT162b2 group on both days 14 and 90. Age was the only factor affecting anti-S-RBD levels in both groups.

Conclusion

In participants previously given two CoronaVac doses, both the mRNA BNT162b2 and viral-vectored AZD1222 boosters showed increased immunogenicity and neutralizing activity against the Delta strain. However, BNT162b2 demonstrated slightly higher immunogenicity and a slower decline over a 3-month period compared to AZD1222.

COVID-19

heterologous vaccination

immunogenicity

Since its emergence in 2019, the coronavirus disease 2019 (COVID-19) pandemic has resulted in significant morbidity and mortality worldwide, including in Thailand. The clinical manifestations of COVID-19 range from mild symptoms such as fever, cough, and rhinorrhea to severe respiratory conditions like pneumonia and acute respiratory distress syndrome, with a risk of multi-organ failure, including acute kidney injury, and death in critical cases [1]. Vaccination remains the most effective public health intervention for mitigating severe COVID-19 outcomes and mortality [2, 3]. Most COVID-19 vaccines target the spike receptor-binding domain (S-RBD) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), eliciting a specific antibody response against this domain in vaccinated individuals [2, 3]. The presence of anti-S-RBD antibodies has also been observed in convalescent serum, thus making this antibody a widely accepted surrogate marker for immunogenicity in response to both vaccination and natural infection [2]. Healthcare workers are at particularly high risk of SARS-CoV-2 exposure [1]. Most of healthcare personnel in Thailand were initially vaccinated with 2 doses of inactivated vaccine, CoronaVac (Sinovac Biotech) which was produced from inactivated wild-type SARS-CoV-2 [4]. However, studies have demonstrated a significant decline in anti-S-RBD antibody titers within two months post-vaccination with CoronaVac, leading to an increased susceptibility to breakthrough infections. Moreover, the rapid evolution of SARS-CoV-2 into variants of concern, such as Alpha and Delta, has compromised the neutralizing efficacy of vaccine-induced antibodies, which are less effective against these variants compared to the ancestral strain [5, 6]. Consequently, booster vaccinations have been recommended, particularly for high-risk populations such as healthcare workers. At the time of this study, available booster options included the viral vector vaccine AZD1222 (Oxford-AstraZeneca) and mRNA vaccines such as BNT162b2 (Pfizer) and mRNA-1273 (Moderna). The objective of this study was to evaluate the immunogenicity of heterologous booster vaccination with AZD1222 or BNT162b2 following a primary two-dose regimen of CoronaVac.

This prospective cohort study was conducted between March and December 2022. Eligible participants were individuals who had completed a two-dose regimen of CoronaVac, with the second dose administered at least 60 days prior to enrollment. Exclusion criteria included a history of COVID-19 infection, receipt of more than two doses of any COVID-19 vaccine, and acute illness or fever (body temperature ≥ 38°C) on the day of booster vaccination. Participants gave informed consent after being briefed on the study's purpose, procedures, risks, and benefits. Participation was voluntary, with the option to withdraw anytime. Confidentiality was ensured, and data was used solely for research. Contact information was provided for inquiries. Ethics approval was obtained from the Ethics Review Committee of the Faculty of Medicine, Thammasat University, Thailand.

Baseline demographic data, medical history, underlying conditions, vaccination history, and COVID-19 infection status were reviewed for eligibility. Participants were given the choice of either the AZD1222 or BNT162b2 booster vaccine on a voluntary basis. Blood samples were collected prior to vaccination and on days 14, 28, and 90 post-vaccination. The immunogenicity of the booster vaccines was assessed by measuring anti-S-RBD IgG levels at baseline, day 14, day 28, and day 90, and surrogate virus neutralization tests (sVNT) were performed on days 14 and 90 to evaluate neutralizing activity against the wild-type SARS-CoV-2 and the Delta variant (B.1.167.2). Anti-S-RBD IgG levels were measured using an in-house enzyme-linked immunosorbent assay (ELISA) technique, and sVNT was performed using an in-house assay kit, both developed by the National Center for Genetic Engineering and Biotechnology (BIOTEC), Bangkok, Thailand, with methodology previously described [7]. SARS-CoV-2-reactive T lymphocytes were evaluated in a subset of 16 participants on day 90 post-booster vaccination using interferon-γ (IFN-γ) ELISPOT assays (Mabtech®) with a Human IFN-γ ELISPOT Pro kit. Given the lack of prior data comparing the immunogenicity of viral vector and mRNA vaccines as boosters following an inactivated vaccine primary series, a sample size of 50 participants per group was proposed.

Statistical analyses included descriptive statistics for continuous variables, which were reported as means with standard deviations (SD) or medians with interquartile ranges (IQR), depending on data distribution. Categorical variables were expressed as percentages. Between-group differences for continuous and categorical variables were assessed using t-tests, Wilcoxon rank-sum tests, and Chi-square tests. Geometric mean titers (GMT) of sVNT against the Delta variant and anti-S-RBD IgG were calculated as exponentiated means of log-transformed data. Correlations between anti-S-RBD IgG levels and sVNT titers were assessed using non-linear regression. All statistical analyses were performed using GraphPad version 8.0.1 (GraphPad®).

Population characteristics

A total of 100 participants were enrolled, with 50 assigned to each booster vaccine group. There were no significant differences between the groups in terms of gender, BMI, or pre-existing conditions. However, participants in the AZD1222 group were significantly older than those in the BNT162b2 group. Additionally, the interval between the second dose of CoronaVac and the booster vaccine was significantly longer in the BNT162b2 group than in the AZD1222 group, likely due to differences in vaccine availability. Baseline characteristics of the study participants are detailed in Table 1.

Comparison of immunogenicity after booster vaccination with BNT162b2 and AZD1222

Following booster vaccination, anti-S-RBD IgG levels increased significantly from baseline in both the BNT162b2 and AZD1222 groups (Table 2 and Figure 1). On day 14 post-vaccination, the fold increase in anti-S-RBD IgG was significantly greater in the BNT162b2 group compared to the AZD1222 group (p<0.0001), with geometric mean fold rises (GMFR) of 40.92-fold (95% CI 33.95-49.32) and 15.65-fold (95% CI 12.80-19.14), respectively. Anti-S-RBD IgG levels declined significantly between day 14 and day 90 in both groups. In the AZD1222 group, the median GMT of anti-S-RBD IgG decreased by 1.7-fold (95% CI 1.511-1.928), while in the BNT162b2 group, the decline was 1.758-fold (95% CI 1.487-2.092), although the between-group difference was not statistically significant.

Neutralizing activity against the Delta variant, as measured by sVNT, was consistent with anti-S-RBD IgG levels. Neutralizing activity increased significantly by day 14 post-booster vaccination in both groups (Figure 2). However, by day 90, neutralizing activity in the BNT162b2 group showed a non-significant decline from day 14 levels, whereas a significant reduction in neutralizing activity was observed in the AZD1222 group (p=0.0011).

At both day 14 and day 90, neutralizing activity against the Delta variant was significantly higher in the BNT162b2 group compared to the AZD1222 group. Furthermore, assessment of SARS-CoV-2 specific memory T cells on day 90 post-booster vaccination revealed a significantly higher frequency of IFN-γ-producing CD4+ T cells in the AZD1222 group than in the BNT162b2 group (p=0.0182) (Figure 3).

Factors associated with immunogenicity

Both univariable and multivariable analyses identified age as the only significant factor influencing the fold rise in anti-S-RBD IgG levels on day 14 post-booster vaccination (Table 3). Interestingly, in the AZD1222 group, the fold rise in anti-S-RBD IgG decreased with increasing age, while in the BNT162b2 group, the fold rise increased with age (Figure 4).

The COVID-19 pandemic led to the implementation of global vaccination campaigns. Numerous studies have shown that antibody titers against SARS-CoV-2 decline over time following primary vaccination with most vaccine platforms. Notably, individuals vaccinated with inactivated vaccines exhibit a more rapid decline in antibody levels compared to those receiving mRNA or viral vector vaccines. As a result, booster doses have been recommended to sustain protective immunity and reduce the incidence of severe disease and mortality [8]. In Thailand, healthcare personnel and high-risk groups were initially vaccinated with CoronaVac. However, breakthrough infections were reported approximately two months after completing the primary series [4], likely due to waning immunity and the emergence of immune-evading variants such as Alpha and Delta. In response, Thailand's Ministry of Public Health recommended booster doses of either AZD1222 or BNT162b2, allowing recipients to choose their preferred vaccine. At the time, the immunogenicity of heterologous booster vaccination was not well characterized, prompting this study to investigate the immune responses elicited by AZD1222 and BNT162b2 boosters in healthcare workers previously vaccinated with two doses of CoronaVac.

Our study demonstrated that anti-S-RBD IgG levels at 60 days or longer post-completion of the two-dose CoronaVac series were insufficient to neutralize the Delta variant. Booster doses with either AZD1222 or BNT162b2 significantly elevated anti-S-RBD IgG levels across all recipients. The BNT162b2 booster produced a significantly higher antibody response than AZD1222, with increased titers observed from day 14 up to day 90 post-vaccination. These findings align with a previous study conducted in Chile by Sue Ann Costa Clemens et al., which reported superior immunogenicity with BNT162b2 compared to AZD1222 or CoronaVac in individuals who had received CoronaVac for at least six months [9]. Interestingly, the GMFR observed in our study differed from their findings, where the GMFR at 28 days post-ChAdOx-1 vaccination was reported as 90 (95% CI 77–104) and 152 (134–173) in the BNT162b2 group. In contrast, our study found a GMFR of 15.65-fold (95% CI 12.80-19.14) for BNT162b2 and 40.92-fold (95% CI 33.95–49.32) for AZD1222. A critical distinction between the two studies was the interval between the primary series and booster dose; the Chilean study used an interval of 182 ± 30 days, while our study had intervals of 87.34 ± 20.08 days for AZD1222 and 109.2 ± 17.64 days for BNT162b2 [9]. These findings suggest that a longer interval between the primary series and booster vaccination may enhance the antibody response more effectively than a shorter interval [10]. The GMFR and post-immunization levels observed in BNT162b2 recipients in our study were significantly higher than those in the AZD1222 group, potentially due to the vaccine’s intrinsic immunogenicity and the longer interval before administration.

The neutralizing activity in our study correlated with the anti-S-RBD IgG levels, consistent with other published reports [11–13]. We focused on the neutralizing activity against the Delta variant, the predominant strain during our study period. Our data indicated that neutralizing activity against the Delta variant remained insufficient 3–4 months after completing the primary vaccination with CoronaVac. However, heterologous booster doses, either with mRNA or vector vaccines, significantly increased neutralizing activity, reaching near 100% efficacy as early as 14 days post-booster. These results affirm the effectiveness of heterologous prime-boost strategies, as supported by previous studies [14, 15]. Furthermore, the durability of neutralizing activity was superior in the BNT162b2 group compared to the AZD1222 group, which aligns with the generally higher humoral immune response observed with mRNA vaccines.

Regarding the cellular immune response, we observed that at 90 days post-booster, there was a significantly higher frequency of SARS-CoV-2-specific memory CD4 + T cells in the AZD1222 group compared to the BNT162b2 group. Both AZD1222 and BNT162b2 elicited robust cellular immune responses, though the nature of these responses differed. AZD1222 tended to induce a Th1-biased response, while BNT162b2 generated a more balanced Th1/Th2 profile [16–18].

Age was identified as the sole demographic factor influencing the antibody response in our cohort. Factors such as sex, ethnicity, BMI, pre-existing conditions, smoking status, and socioeconomic status are known to influence anti-S-RBD IgG levels following COVID-19 vaccination. These variables can modulate immune responsiveness, impacting vaccine efficacy across diverse populations [19, 20].

This study has several limitations. The small sample size in each cohort may limit the statistical power to identify factors affecting immunogenicity, such as comorbidities (e.g., diabetes, hypertension, obesity) and immunosuppressive therapy. Additionally, the evolving nature of the COVID-19 outbreak, characterized by the emergence of genetically divergent strains, necessitates further investigation into the neutralizing capabilities of the vaccines against these variants. The genetic drift from the ancestral strain may result in diminished vaccine efficacy in preventing infection or mitigating disease severity.

This study assessed the immunogenicity of booster vaccination against COVID-19 in individuals who had previously received two doses of the inactivated CoronaVac vaccine, followed by a third booster dose with either the mRNA vaccine BNT162b2 or the viral-vectored vaccine AZD1222. Both booster vaccines induced higher immunogenicity and neutralization capabilities against the Delta variant of COVID-19. However, BNT162b2 demonstrated slightly higher immunogenicity than AZD1222, while AZD1222 elicited a more pronounced cellular response.

COVID-19: coronavirus disease 2019

GMFR geometric mean fold rise

GMT: Geometric mean titers

IgG: Immunoglobulin G

IFN-γ: interferon-γ

IQR: interquartile ranges

SARS-CoV-2: severe acute respiratory syndrome coronavirus 2

SD: standard deviations

S-RBD: spike receptor-binding domain

sVNT: surrogate virus neutralization tests

Ethics approval and consent to participate: Ethics approval was obtained from the Human Ethics Committee of Thammasat University (Medicine), Thammasat University, Thailand. Informed consent was obtained from all subjects involved in the study.

Consent for publication: Not applicable

Availability of data and materials: Nanthapisal, Sira (2024), “The comparison of Immune response to Third booster dose with of ChAdOx-1 or BNT162b2 COVID-19 vaccine in healthcare workers after receiving two doses of CoronaVac”, Mendeley Data, V1, doi: 10.17632/hs35bmzv4r.1

Competing interests: The authors declare no conflicts of interest related to this study. No financial or personal relationships have influenced the research or its outcomes.

Funding: Thammasat University Research Fund

Authors' contributions:

Conceptualization and methodology AT, SK, SN, PA, PJ
Investigation PB, PP, SN, SK
Analysis and interpretation of data AT, SK, SN, PA, PJ, PK
Data Curation AT, SN, PJ, PA
Writing – Original Draft Preparation SK, SN
Writing – Review & Editing SN, PJ, PA
Visualization SN
Project Administration SK, AT, SN
Funding Acquisition AT
All authors approved the submitted version and agrees to be personally accountable for the author’s own contributions

Acknowledgements: The authors would like to thank “Medicine Thammasat University Clinical Research Center” for the study operation

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Table 1 Baseline characteristics of participants

Characteristics	ChAdOx-1 (n=50)	BNT162b2 (n=50)	p-value
Age (years) mean±SD	42.82±6.01	37.3±8.07	0.0002
Sex Male, n (%) Female, n (%)	16 (32) 32 (64)	16 (32) 32 (64)	>0.9999
BMI mean±SD	22.65±3.19	22.35±3.44	0.6487
Pre-existing condition
Diabetes Mellitus	1 (2)	0 (0)	0.018
Hypertension	7 (14)	1 (2)	0.0594
Dyslipidemia	9 (18)	4 (8)	0.2336
Thyroid disease	2 (4)	0 (0)	0.4949
Asthma	1 (2)	0 (0)	>0.9999
Allergic rhinitis	8 (16)	10 (20)	0.7953
Autoimmune disease	1 (2)	0 (0)	>0.9999
Chronic lung disease	0 (0)	0 (0)	1.000
Cancer	0 (0)	0 (0)	1.000
Interval between 2^nd and 3^rd dose (day) mean±SD)	87.34±20.08	109.2±17.64	<0.0001

Table 2 Geometric mean titer of spike-receptor binding domain IgG antibody (anti-SRBD IgG) in each group

	ChAdOx-1 (n=50)	BNT162b2 (n=50)	p-value
Baseline	106.7 (90.09, 126.4)	87.94 (75.17, 102.9)	0.0675
Day 14	1670 (1440, 1938)	3556 (3272, 3865)	<0.0001
Day 28	1578 (1388, 1794)	2844 (2624, 3082)	<0.0001
Day 90	974.6 (845.4, 1124)	2076 (1833, 2350)	<0.0001

Data were presented in median( IQR), analyzed using Wilcoxon rank sum (Mann Whitney) test

Table 3 Univariate and multivariate logistic analysis of factors associated with fold rise of anti-spike receptor binding domain IgG at day 14 after booster vaccine in individuals 14-day fold increase in immunity levels before and after vaccination who received booster vaccine for more than 90 days.

	Univariate logistic analysis			Multivariate logistic analysis
	Odd ratio	95% interval	P value	Odd ratio	95% interval	P value
AZD1222
Sex	-1.425	-10.80 to 7.949	0.7612	-14.58	-30.34 to 1.189	0.069
Body weight	-0.03364	-0.4031 to 0.3358	0.8555	-4.285	-10.00 to 1.433	0.1379
BMI	0.1902	-1.218 to 1.599	0.2887	11.81	-3.406 to 27.03	0.1248
Age	-1.056	-1.799 to -0.3133	0.0067	-1.044	-1.952 to -0.1364	0.0252
Pre-existing condition	5.146	-3.735 to 14.03	0.2498	5.556	-3.848 to 14.96	0.2398
Interval between 2^nd and 3^rd dose	-0.09933	-0.3211 to 0.1224	0.3722	-0.1091	-0.3332 to 0.1150	0.3314
BNT162b2
Sex	-10.9	-30.85 to 9.042	0.2769	3.298	-26.48 to 33.08	0.8241
Weight	0.6136	-0.1632 to 1.390	0.1187	-7.574	-21.79 to 6.646	0.2881
BMI	1.888	-0.9051 to 4.681	0.1803	21.51	-16.47 to 59.49	0.2591
Age	1.495	0.3744 to 2.617	0.01	1.571	0.2382 to 2.904	0.0221
Pre-existing condition	6.137	-16.38 to 28.66	0.5485	-1.693	-26.62 to 23.23	0.8915
Interval between 2^nd and 3^rd dose	0.09429	-0.4684 to 0.6569	0.7374	-0.09902	-0.6881 to 0.4900	0.7358

No competing interests reported.

The comparison of Immune response to Third booster dose with of ChAdOx-1 or BNT162b2 COVID-19 vaccine in healthcare workers after receiving two doses of CoronaVac

Status:

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Abstract

Figures

Background

Methods

Results

Discussion

Conclusions

Abbreviations

Declarations

References

Tables

Additional Declarations

Status:

Version 1