Serological response after COVID-19 mRNA-1273 booster dose in immunocompromised patients, Taiwan, July to August 2021

Background: Whether immunocompromising conditions affect the immunogenicity of COVID-19 booster vaccination remains a concern, which impedes the vaccination campaign in people most vulnerable to COVID-19-associated morbidity and mortality. We aimed to evaluate the effect of immune dysfunction on immunogenicity of homologous and heterologous prime-boost COVID-19 vaccination. Methods: Between July and August, 2021, 399 participants were randomized to receive ChAdOx1/ChAdOx1 8 weeks apart, ChAdOx1/mRNA-1273 8 weeks apart, ChAdOx1/mRNA-1273 4 weeks apart, and mRNA-1273/mRNA-1273 4 weeks apart. The anti-SARS-CoV-2 spike IgG antibody titers on the day before booster vaccination and 4 weeks after booster vaccination were compared between participants with and without immunocompromising conditions. Results: Among ChAdOx1-primed participants, a trend of lower anti-SARS-CoV-2 spike IgG titers before booster vaccination were found in participants with autoimmune diseases (geometric means, 34.76 vs. 84.25 binding antibody units [BAU]/mL, P = 0.173), compared to those without. Participants receiving immunosuppressants and/or immunomodulators had significant lower anti-SARS-CoV-2 spike IgG titers before booster vaccination than those without (geometric means, 36.39 vs. 83.84 BAU/mL; P = 0.001). Among mRNA-1273-boosted participants, anti-SARS-CoV-2 spike IgG titers 4 weeks after booster vaccination were similar across all the strata. Participants with autoimmune diseases and receiving immunosuppressants and/or immunomodulators, had numerically lower anti-SARS-CoV-2 spike IgG titers 4 weeks after booster vaccination compared to those without (geometric means, 1474.34 vs. 1923.23 and 1590.61 vs. 1918.38 BAU/mL; P > 0.05). Conclusion: The immunogenicity of prime vaccination with ChAdOx1 decreased by immune dysfunction, but enhanced after receiving boost vaccination with mRNA-1273. Our study results support the efficacy of mRNA-1273 booster dose among immunocompromised hosts.