CoronaVac Aşısının İkinci Dozu COVID-19 Geçirmiş Kişilerde Antikor Düzeylerinin Düşmesine Neden Olabilir The Second Shot of CoronaVac Vaccine May Cause Reduction of Antibody Levels in People who Previously had COVID-19 Aynur Eren TOPKAYA 1 (ID), Ali Ümit KESKİN 2 (ID), Altay Burak DALAN 3 (ID), Pınar ÇIRAGİL 1 (ID) 1 Yeditepe Üniversitesi Tıp Fakültesi, Tıbbi Mikrobiyoloji Anabilim Dalı, İstanbul. 1 Yeditepe University Faculty of Medicine, Department of Medical Microbiology, İstanbul, Turkey. 2 Yeditepe Üniversitesi Mühendislik Fakültesi, Biyomedikal Mühendislii Anabilim Dalı, İstanbul. 2 Yeditepe University Faculty of Engineering, Department of Biomedical Engineering, İstanbul, Turkey. 3 Yeditepe Üniversitesi Tıp Fakültesi, Tıbbi Biyoloji Anabilim Dalı, İstanbul. 3 Yeditepe University Faculty of Medicine, Department of Medical Biology, İstanbul, Turkey. ABSTRACT The CoronaVac vaccine is an inactivated type two-dose regimen vaccine developed and manufactured by Sinovac Life Sciences Company, in China. It has already been used in China’s vaccination program, while 21 other countries (including Indonesia, Turkey and Brazil) also granted emergency use authorization for this vaccine. In Turkey, on January 14, 2021, healthcare workers (HCWs) started to be vaccinated with CoronaVac as the priority group in vaccination. An important question that arose at this time was about how the vaccination schedule would be for people who had previously had Coronavirus disease 2019 (COVID-19). The Centers for Disease Control and Prevention (CDC) recommends that those who have had a previous COVID-19 infection can be vaccinated regardless of their previous infection. CDC guidelines also mention that “…if antibody (Ab) testing was done after the frst dose of an mRNA vaccine, the vaccination series should be completed regardless of the Ab test result”. It should be noted here that this statement applies particularly to mRNA type vaccines, whereas CoronaVac jab is an inactivated type two-dose regimen vaccine. The aim of this study was to present interim results of our ongoing study to compare the effect of two doses of inactivated CoronaVac vaccine on humoral immunity of people who had previously severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, and those people who did not have the infection. In our study, CoronaVac jab containing 600 SU inactivated SARS-CoV-2 antigen was administered as 0.5 ml to 62 HCWs in Yeditepe University Hospital (Istanbul, Turkey), in accordance with the manufacturer’s recommendations. Ab levels against spike receptor binding region of SARS-CoV-2 were measured quantitatively. SARS-CoV-2 IgG assay were performed using Abbott Architect i2000 instrument (Abbott Laboratories, Abbott Park, IL, USA). Ab titers were measured before vaccination (Ab0), one month after the frst vaccination (Ab1), and one month after the second vaccination (Ab2). The Ab responses of 62 HCWs before and after CoronaVac vaccination were determined. Two groups were created. Group 1 consisted of 18 females and 15 males Editöre Mektup/Letter to the Editor İletişim (Correspondence): Prof. Dr. Pınar Çıragil, Yeditepe Üniversitesi, Enfeksiyon Hastalıkları ve Klinik Mikrobiyoloji, Kozyatağı Hastanesi, 34752 Ataşehir/İstanbul. Tel (Phone): 0 (216) 578 00 00, E-posta (E-mail): pinar.ciragil@yeditepe.edu.tr Mikrobiyol Bul 2022;56(1):139-142/ doi: 10.5578/mb.20229913 Geliş Tarihi (Received): 05.08.2021 • Kabul Ediliş Tarihi (Accepted): 21.10.2021 Makale Atıfı: Topkaya AE, Keskin AÜ, Dalan AB, Çıragil P. CoronaVac aşısının ikinci dozu COVID-19 geçirmiş kişilerde antikor düzeylerinin düşmesine neden olabilir. Mikrobiyol Bul 2021;53(2):139-142.