Assessment of Serum Levels of Vitamin D and Selected Biochemical and Hematological Parameters in Rats Post-Immunized with Inactivated COVID-19 Virus.

Serum levels of vitamin D (VD) are inversely correlated with the incidence or severity of COVID-19. This study aimed to investigate the effects of inactivated COVID-19 virus (ICoV-19) immunization on VD levels, as well as biochemical and hematological parameters in adult male Sprague-Dawley rats. Twenty rats were randomly divided into two groups of 10: the control group (group I) and the ICoV-19-receiving group (group II). Aluminum hydroxide and a single dose of ICoV-19 (10⁷ TCID50 of the HB02 strain of the COVID-19 virus) were administered subcutaneously to rats in groups I and II, respectively. After two weeks (on day 14), booster doses were administered to both groups. Blood samples were collected from the rats in both groups primarily for the experiment and 21 days after the second administration (on day 35). Samples were then stored frozen until analysis. There were no significant differences in VD levels between the two groups on day 0, but on day 35, VD levels in group II had significantly decreased, compared to group I (P<0.05). Additionally, group II had higher concentrations of fibrinogen, blood urea nitrogen, creatinine, and lactate dehydrogenase activity than group I (P<0.05). Group II also showed a significant increase in neutrophil counts and neutrophil-to-lymphocyte ratio after 35 days (P<0.05), while lymphocyte counts decreased. These findings suggest that VD may play a role in preventing COVID-19 and can thus be a potential candidate for managing and controlling the disease.