[The Second Shot of CoronaVac Vaccine May Cause Reduction of Antibody Levels in People who Previously had COVID-19]. / CoronaVac Asisinin Ikinci Dozu COVID-19 Geçirmis Kisilerde Antikor Düzeylerinin Düsmesine Neden Olabilir.

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 first 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 first 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 who were tested as COVID-19 positive, previously. Group 2 consisted of 20 females and 9 males who never had the infection. Minimum, median and maximum Ab0 values of Group1 were 1.6, 180.8 and 5582.6, respectively and Ab1 values were 26.3, 1005.7 and 3923.1; Ab2 values were 202.1, 1119.1 and 2885.9, (in au/mL) respectively. On the other hand, minimum, median and maximum Ab0 values of Group 2 were 0.1, 1.8, and 37.2, Ab1 values were 4.7, 72.7, 470.2, and Ab2 values were 270.3, 746.2 and 5554.1, respectively. In Group 1, 20 of the HCWs showed lower Ab2 titers, while 13 of the HCWs showed higher Ab2 titers than the Ab1 titers. Whereas in Group2 all HCWs had higher Ab2 titers than the Ab1 titers. When the increasing and decreasing Ab2 titers of both groups were evaluated with the 2×2 contingency table and Fisher's exact chi-square test, a statistically significant difference was found between the groups (p<0.001). As a result, we think that a single dose of CoronaVac vaccine similarly to mRNA vaccines can be administered to people who have had COVID-19 due to the possibility that the Ab levels measured after the first dose of vaccine will decrease after the second dose of vaccine.