Immunogenicity and Safety of the Third Booster Dose with mRNA-1273 COVID-19 Vaccine after Receiving Two Doses of Inactivated or Viral Vector COVID-19 Vaccine

The changes in the severe acute respiratory syndrome coronavirus 2 and the tapering of immunity after vaccination have propelled the need for a booster dose vaccine. We aim to evaluate B and T cell immunogenicity and reactogenicity of mRNA-1273 COVID-19 vaccine (100 mu g) as a third booster dose after receiving either two doses of inactivated COVID-19 vaccine (CoronaVac) or two doses of viral vector vaccine (AZD1222) in adults not previously infected with COVID-19. The anti-receptor-binding-domain IgG (anti-RBD IgG), surrogate virus neutralization test (sVNT) against the Delta variant, and Interferon-Gamma (IFN-gamma) level were measured at baseline, day (D)14 and D90 after vaccination. In D14 and D90, the geometric means of sVNT were significantly increased to 99.4% and 94.5% inhibition in CoronaVac, respectively, whereas AZD1222 showed inhibition of 99.1% and 93%, respectively. Anti-RBD IgG levels were 61,249 to 9235 AU/mL in CoronaVac and 38,777 to 5877 AU/mL in AZD1222 after D14 and D90 vaccination. Increasing median frequencies of S1-specific T cell response by IFN-gamma concentration were also elevated in D14 and were not significantly different between CoronaVac (107.8-2035.4 mIU/mL) and AZD1222 (282.5-2001.2 mIU/mL). This study provides evidence for the high immunogenicity of the mRNA-1273 booster after two doses of CoronaVac or AZD1222 in the Thai population.

Automated summary

The study evaluated the B and T cell immunogenicity and reactogenicity of the mRNA-1273 COVID-19 booster vaccine in adults who had previously received two doses of either the CoronaVac or AZD1222 vaccine. Results showed that the booster vaccine significantly increased the immune response, as indicated by higher levels of anti-RBD IgG and sVNT inhibition. The T cell response was also enhanced, with similar increases in both vaccine groups. This study provides evidence for the effectiveness of the mRNA-1273 booster in the Thai population.