Wullimann et al.
Antigen-specific T cell responses following single and co-administration of tick-borne encephalitis, Japanese encephalitis, and yellow fever virus vaccines: Results from an open-label, non-randomized clinical trial-cohort. PLoS Negl Trop Dis. 2025;19:e0012693. doi:10.1371/journal.pntd.0012693
An open-label, non-randomized clinical study was conducted involving 140 healthy participants who received either single or concomitant administration of licensed flavivirus vaccines targeting tick-borne encephalitis virus (TBEV), Japanese encephalitis virus (JEV), and yellow fever virus (YFV). The vaccines included an inactivated alum-adjuvanted TBE vaccine, an inactivated alum-adjuvanted JEV vaccine, and a live-attenuated YFV 17D strain vaccine. CD4+ and CD8+ T cell responses were analyzed following vaccination.
T cell responses were assessed using virus-specific peptides derived from the envelope protein, capsid protein, and non-structural protein 5 of the aforementioned viruses, as well as from Zika virus (ZIKV), to evaluate cross-reactivity and immune activation.
The magnitude and specificity of CD4+ and CD8+ T cell responses to the respective viral antigens remained largely unaffected by the concomitant administration of the flavivirus vaccines. Whether administered in the same or in different upper arms, co-delivery had minimal impact on cellular immune responses.
The authors concluded that the co-administration of three commonly used, licensed flavivirus vaccines is feasible. It does not increase the risk of adverse events nor significantly compromise the induction of virus-specific neutralizing antibodies (see Snapshot Week 13/2023) or T cell-mediated immunity.