Vaccination with inactivated SARS-CoV-2 vaccine TURKOVAC induces durable humoral and cellular immune responses up to 8 months

Seçil Yılmaz ¹ Ahmet Eken ² zafer sezer ³ Burcu Şen Bağcı ⁴ Şerife Erdem ⁵ Medine Doğan Sarıkaya ⁵ Büşra Kaplan ⁴ Ahmet Inal ³ Adnan Bayram ³ Gamze KALIN UNUVAR ³ Gokmen Zararsız ³ İlayda Yerlitaş ³ Nuri Cakir ³ SHAIKH TERKIS ISLAM PAVEL ⁴ MUHAMMET ALİ UYGUT ⁴ Hazel Yetiskin ⁴ Ates Kara ⁶ Aykut Ozdarendeli ^7*

• ¹ Erciyes University, Kayseri, Türkiye
• ² School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
• ³ Faculty of Medicine, Erciyes University, Kayseri, Türkiye
• ⁴ Vaccine Research and Development Application and Research Center, Erciyes University, Kayseri, Türkiye
• ⁵ Genome and Stem Cell Center, Erciyes University, Kayseri, Türkiye
• ⁶ Hacettepe University Hospital, Ankara, Ankara, Türkiye
• ⁷ Department of Microbiology, Faculty of Medicine, Erciyes University, Kayseri, Türkiye

Background: The rapid spread of the SARS-CoV-2 virus has led to a global health crisis, necessitating swift responses in medical science, mainly through vaccination strategies. While shortterm vaccine effectiveness is evident, immune protection's long-term effects and duration remain Deleted: inactive Deleted: particular 29 Deleted: the 30 Deleted: of immune protection incompletely understood. Systematic monitoring of these responses is essential for optimizing vaccination strategies.Aims: This study aimed to explore the durability of antigen-specific T and B cell responses and antibody levels up to 8 months post-immunization with the inactivated TURKOVAC vaccine in volunteers. Additionally, the impact of two versus three doses of vaccination on these parameters was analyzed.Methods: Volunteers (n = 80) received two or three doses of TURKOVAC. Spike-specific B cells, CD4⁺ T cells, CD8⁺ T cells, and antibody levels were measured at multiple time points postimmunization.Results: Spike-specific B cells remained elevated up to 8 months post-immunization. SARS-CoV-2specific CD4⁺ and CD8⁺ T cells peaked at 4 months but declined thereafter. TURKOVAC resulted in durable antigen-specific humoral and cellular immune memory with distinct kinetics. Still, most assessments observed no significant differences between two and three doses, except for antigen specific-IL-2 and CD4⁺ LAMP1 responses.Conclusions: TURKOVAC vaccination induces durable immune responses, with spike-specific B cells persisting up to 8 months and T cell responses peaking at 4 months before declining. These findings suggest that TURKOVAC contributes to long-term immune protection against SARS-CoV-2. 1 Deleted: the duration of immune responses require further 71 investigation. 72 Deleted: with the TURKOVAC inactive vaccine in volunteers. 73 Additionally, the impact of 2 versus 3 immunizations on these 74 parameters was analyzed. 75 Deleted: either 76 Deleted: Volunteers (n=80) received 2 or 3 doses of TURKOVAC. 77 Spike-specific total B cells, SARS-CoV-2 specific CD4+ and CD8+ 78 T cells, and antibody levels were measured at multiple time points 79 post-immunization.