COVAX 19

It has been demonstrated that COVID-19 vaccines confer significant protection, but temporal decay in the vaccine-induced antibodies has been reported; therefore, a third booster dose was considered. Human leukocyte antigen (HLA) class II molecules act as antigen presenting structures, play critical roles in the formation of an efficient antibody response. The current study aimed to evaluate the anti-receptor binding domain (RBD) antibody response after the booster dose of SpikoGen® vaccine in individuals with a history of Sinopharm primary vaccination series and its association with HLA-DQB1 and -DRB alleles.

Whole blood samples were drawn from 95 eligible individuals before and three weeks after the booster dose of SpikoGen®. Quantitative measurement of anti-RBD IgG and qualitative assessment of anti-RBD IgA was performed using the ELISA method and HLA-DQB1 and -DRB loci were genotyped by low-resolution SSP-PCR method.

A significant increase was observed in the anti-RBD IgG antibodies after the booster dose of SpikoGen® (baseline: 1.82 ± 0.55 GMT, after: 2.28 ± 0.36 GMT)(P < 0.0001). The median fold change of anti-RBD IgG antibodies for DRB1*14 positive individuals (3.96 (1.47-31.75)) was significantly higher than DRB1*14 negative people (1.18 (1.08-1.34))(P = 0.008). In addition, the median fold change of anti-RBD IgG antibodies for DQB1*04 positive individuals (1.39 (1.21-3.43)) was higher than those which were DQB1*04 negative (1.18 (1.08-1.34)), however it was marginally significant (P = 0.060). The seroconversion incidence for anti-RBD IgA antibodies was 68.42 %.

In conclusion, our study showed that the booster dose of SpikoGen® can elicit a robust anti-RBD antibody response which was positively associated with DRB1*14 allele.

Recombinant protein vaccines represent a well-established, reliable and safe approach for pandemic vaccination. SpikoGen® is a recombinant spike protein trimer manufactured in insect cells and formulated with Advax-CpG55.2 adjuvant. In murine, hamster, ferret and non-human primate studies, SpikoGen® consistently provided protection against a range of SARS-CoV-2 variants. A pivotal Phase 3 placebo-controlled efficacy trial involving 16,876 participants confirmed the ability of SpikoGen® to prevent infection and severe disease caused by the virulent Delta strain. SpikoGen® subsequently received a marketing authorization from the Iranian FDA in early October 2021 for prevention of COVID-19 in adults. Following a successful pediatric study, its approval was extended to children 5 years and older. Eight million doses of SpikoGen® have been delivered, and a next-generation booster version is currently in development. This highlights the benefits of adjuvanted protein-based approaches which should not overlook when vaccine platforms are being selected for future pandemics.