Immunogenicity & safety of intradermal ChAdOx1 nCoV-19 boost in healthy populations

Severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) has caused a global pandemic. Two doses of an inactivated SARS-CoV-2 vaccine (CoronaVac) were insufficient to protect against variants of concern (VOCs), while viral vector vaccines remain protective against the infection. Here we conducted a preliminary study to evaluate safety and immunity in adult population who received conventional 2 dosage-regimen of inactivated SARS-CoV-2 vaccine with additional intradermal ChAdOx1 nCoV-19 reciprocal dosage (1:5). Intramuscular ChAdOx1 nCoV-19 boost was also included as a control. Immediate and delay local reactions were frequently observed in the fractional intradermal boost but systemic side effects were significantly decreased compared to the conventional intramuscular boost. The anti-RBD-IgG levels, the neutralizing function against delta variants and T cell responses were significantly increased after boosting with both routes. Taken together, reciprocal dosage of intradermal ChAdOx1 nCoV-19 boost induces similar humoral and cellular immune responses and offers less systemic adverse reactions compared to full dose of intramuscular boosting. These findings provide an effective vaccine management during the shortage of vaccine supply.

Dr. Nawamin Pinpathomrat is a lecturer at the Department of Biomedical Science, Medicine at Prince Songkla University. He did his DPhil at the Jenner institute, University of Oxford on pre-clinical development of a viral vector TB vaccine. Interesting fact – in the last year of his DPhil, he unexpectedly ended up being a MasterChef UK Finalist 2018 so do check out his crab dance that has became viral across social media! His current research focuses on safety and immunogenicity of COVID-19 vaccines comparing different regimens and routes of vaccination. Antibody responses are analysed using ELISA and Plaque reduction neutralization tests. ELISpot and flow cytometry are used to observe T cell phenotypes and their effector function.