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. 2022 Jan 24;40(3):524-530.
doi: 10.1016/j.vaccine.2021.11.083. Epub 2021 Dec 3.

Immunogenicity of a third dose viral-vectored COVID-19 vaccine after receiving two-dose inactivated vaccines in healthy adults

Ritthideach Yorsaeng  1 , Nungruthai Suntronwong  1 , Harit Phowatthanasathian  1 , Suvichada Assawakosri  1 , Sitthichai Kanokudom  1 , Thanunrat Thongmee  1 , Preeyaporn Vichaiwattana  1 , Chompoonut Auphimai  1 , Lakkhana Wongsrisang  1 , Donchida Srimuan  1 , Thaksaporn Thatsanatorn  1 , Sirapa Klinfueng  1 , Natthinee Sudhinaraset  1 , Nasamon Wanlapakorn  1 , Yong Poovorawan  2
Affiliations

Immunogenicity of a third dose viral-vectored COVID-19 vaccine after receiving two-dose inactivated vaccines in healthy adults

Ritthideach Yorsaeng et al. Vaccine. .

Abstract

In June 2021, Thailand was hit by the delta variant of SARS-CoV-2 resulting in the biggest wave of COVID-19. Due to the widespread delta variant, more than 600 healthcare workers had COVID-19 despite completion of two-dose CoronaVac. The Ministry of Public Health recommended that healthcare workers received a third dose of AZD1222 to increase level of protection against SARS-CoV-2. However, immune response after the AZD1222 booster in individuals who completed the two-dose CoronaVac vaccine are limited. In this study, sera from those who received a booster of AZD1222 in June-July 2021 were tested for SARS-CoV-2 spike receptor-binding-domain (RBD) IgG, anti-RBD total immunoglobulins and anti-spike protein 1 (S1) IgA. The neutralizing activities in a subset of serum samples were tested against the wild type and variants of concern (B.1.1.7, B.1.617.2, and B.1.351) using an enzyme-linked immunosorbent assay-based surrogate virus neutralization test. Participants who received the booster of AZD1222 possessed higher levels of spike RBD-specific IgG, total immunoglobulins, and anti-S1 IgA than the two-dose vaccinees (p < 0.001). They also elicited higher neutralizing activity against the wild type and all variants of concern than the recipients of the two-dose vaccines. This study demonstrated a high immunogenicity of the AZD1222 booster in individuals who completed the two-dose inactivated vaccines.

Keywords: Booster dose; COVID-19; Immunogenicity; Inactivated vaccine; Virus vector.

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Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Schematic diagram of this study. Three groups of vaccinees and samples done for each test are depicted. Randomly selected samples subjected to testing listed as numbers under each group.
Fig. 2
Fig. 2
Immunoassays for SARS-CoV-2 in serum samples from fully vaccinated and unvaccinated convalescent COVID-19 patients. (a) Total anti-RBD immunoglobulins. (b) Anti-RBD IgG. (c) Anti-S1 IgA. (d) Surrogate virus neutralization test (sVNT). Geometric mean titer (GMT) with 95% confidence intervals are shown as red lines within each group. * denotes p < 0.05 and *** denotes p ≤ 0.001.
Fig. 3
Fig. 3
Surrogate virus neutralization test against SARS-CoV-2 wild-type and variants. (a) Wild-type. (b) B.1.1.7. (c) B.1.351. (d) B.1.617.2. Percent inhibition is shown with mean and IQR (red lines). *** denotes p ≤ 0.001.
Fig. 4
Fig. 4
Comparison between neutralizing activities against variants relative to the wild type in serum samples obtained from (a) two-dose CoronaVac/CoronaVac, (b) two-dose AZD1222/AZD1222, and (c) two-dose CoronaVac + one-dose AZD1222 vaccinees. *** denotes p ≤ 0.001. ** denotes p ≤ 0.01.
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