Ameliorated immunity elicited by intradermal inoculation in individuals vaccinated with inactivated SARS-CoV-2 vaccine

Abstract

In clinical trials, antibodies against SARS-CoV-2 were almost eliminated in participants six months after immunization with an inactivated SARS-CoV-2 vaccine. The short duration of antibody persistence is an urgent problem. In this study, the problem was solved by intradermal inoculation with trace antigen. Within 72 h after intradermal inoculation, slight inflammatory reactions, such as redness and swelling, were observed at the inoculation site of the participants. On the 7th, 60th and 180th days after inoculation, the antibodies of the participants were detected, and it was found that the neutralizing antibody and ELISA (IgGs) anti-S antibody levels rapidly increased and were maintained for 6 months. These results indicate that there was a SARS-CoV-2-specific immune response in the participants immunized with an inactivated SARS-CoV-2 vaccine, which could be quickly and massively activated by intradermal trace antigen inoculation to produce an effective clinically protective effect.

Keywords: Antibody; Antigen inoculation; Intradermal immunization; SARS-CoV-2.

Fig. 1

Schematic depicting the immunization schedule.

Fig. 2

Immune response induced by intramuscular immunization with an inactivated SARS-CoV-2 vaccine in adults. Neutralizing antibodies (A), ELISA (IgGs) anti-S antibodies (B) and ELISA (IgGs) anti-N antibodies (C) whose production was induced by an inactivated vaccine in a clinical trial in participants assigned to the 0- and 14-day schedule at 28, 42 and 192 days after intramuscular immunization. Statistical significance was assessed by unpaired t tests (*p < 0.05, **p < 0.01).

Fig. 3

Clinical observations at the inoculation site in participants Clinical observation of redness in the appearance of the skin at 0 h (A), 24 h (B), 36 h (C), 48 h (D) and 72 h (E) post inoculation. The red scale is 0.5 cm. Statistical analysis of skin redness in participants at 0 h, 24 h, 36 h, 48 h and 72 h post inoculation. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Immune response induced by trace antigen in individuals vaccinated with an inactivated SARS-CoV-2 vaccine Neutralizing antibodies (A), ELISA (IgGs) anti-S antibodies (B) and ELISA (IgGs) anti-N antibodies (C) whose production was induced by an inactivated vaccine in individuals 7, 60 and 180 days after intradermal injection. Statistical significance was assessed by unpaired t tests (*p < 0.05, **p < 0.01, ****p < 0.0001).