Immunogenicity and reactogenicity of accelerated regimens of fractional intradermal COVID-19 vaccinations

Abstract

Introduction: This phase I study explored the immunogenicity and reactogenicity of accelerated Q7 fractional intradermal vaccination regimens for COVID-19. Methods: Participants (n = 60) aged 18-60 years na?ve to SARS-CoV-2 infection or vaccination were randomly allocated into one of four homologous or heterologous accelerated two-dose two-injection intradermal regimens seven days apart:(1) BNT162b2-BNT162b2(n= 20) (2) ChAdOx1- BNT162b2 (n = 20) (3) CoronaVac-ChAdOx1 (n = 10) and (4) ChAdOx1-ChAdOx1 (n = 10). CoronaVac and ChAdOx1 were 20% and BNT162b2 17% of their standard intramuscular doses (0.1 mL and 0.05 mL per injection respectively). Humoral immune responses were measured through IgG response towards receptor binding domains (RBD-IgG) of ancestral SARS-CoV-2 spike protein and pseudovirus neutralization tests (PVNT50). Cellular immune responses were measured using ELISpot for ancestral protein pools. Results: Immunogenicity was highest in regimen (2) followed by (1) (4) and (3) 2 weeks after the second dose (P < 0.001 for anti-RBD-IgG and P= 0.01 for PVNT50). Each group had significantly lower anti-RBD IgG (by factors of 5.4 3.6 11.6 and 2.0 for regimens (1) to (4) respectively) compared to their respective standard intramuscular regimens (P < 0.001 for each). Seroconversion rates for PVNT50 against the ancestral strain were 75% 90% 57% and 37% for regimens (1) to (4) respectively. All participants elicited ELISpot response to S-protein after vaccination. Adverse events were reportedly mild or moderate across cohorts. Discussion: We concluded that accelerated fractional heterologous or homologous intradermal vaccination regimens of BNT162b2 and ChAdOx1 were well tolerated provided rapid immune priming against SARS-CoV-2 and may prove useful for containing future outbreaks. Copyright ? 2023 Niyomnaitham Atakulreka Wongprompitak Copeland Toh Licciardi Srisutthisamphan Jansarikit and Chokephaibulkit.