COVID-19 mRNA booster vaccine induces transient CD8+ T effector cell responses while conserving the memory pool for subsequent reactivation.

Immunization with two mRNA vaccine doses elicits robust spike-specific CD8+ T cell responses, but reports of waning immunity after COVID-19 vaccination prompt the introduction of booster vaccination campaigns. However, the effect of mRNA booster vaccination on the spike-specific CD8+ T cell response remains unclear. Here we show that spike-specific CD8+ T cells are activated and expanded in all analyzed individuals receiving the 3rd and 4th mRNA vaccine shots. This CD8+ T cell boost response is followed by a contraction phase and lasts only for about 30-60 days. The spike-specific CD8+ T memory stem cell pool is not affected by the 3rd vaccination. Both 4th vaccination and breakthrough infections with Delta and Omicron rapidly reactivate CD8+ T memory cells. In contrast, neutralizing antibody responses display little boost effect towards Omicron. Thus, COVID-19 mRNA booster vaccination elicits a transient T effector cell response while long-term spike-specific CD8+ T cell immunity is conserved to mount robust memory recall targeting emerging variants of concern.

Nosocomial acquisition of dengue.

Recent transmission of dengue viruses has increased in tropical and subtropical areas and in industrialized countries because of international travel. We describe a case of nosocomial transmission of dengue virus in Germany by a needlestick injury. Diagnosis was made by TaqMan reverse transcription-polymerase chain reaction when serologic studies were negative.