The coronavirus disease 2019 (COVID-19) pandemic is a global crisis, with devastating health, business and social impacts. Vaccination is a safe, simple, and effective way of protecting a person against COVID-19. By the end of August 2021, only 24.6% of the world population has received two doses of a COVID-19 vaccine. Since the emergence of COVID-19, several COVID-19 vaccines have been developed and approved for emergency use. Current vaccines have shown efficacy with low risk of adverse effects. However, COVID-19 vaccines have been related to a relatively small number of cases of heart inflammation, anaphylaxis (allergic reactions), and blood clots formation. On the other hand, COVID-19 vaccination is not recommended for children less than 12 years of age. Furthermore, It has been proposed that some new variants (e.g., Lambda and Delta) are proficient in escaping from the antiviral immunity elicited by vaccination. Herein we present current considerations regarding the COVID-19 vaccines including: efficacy against new variants, challenges in distribution, disparities in availability, dosage gender and race difference, COVID-19 vaccine transport and storage, limitations in children and pregnant women. Long-time monitoring is essential in order to find vaccine efficacy and to rule out related side effects.

Background and aims Nanoparticles could represent a therapeutic approach for the treatment of various diseases. It has been reported that cerium oxide nanoparticles (CeO 2 NPs) have potential useful effects. Therefore, we aimed to examine the protective effects of the CeO 2 NPs in two models of liver injury, non-alcoholic fatty liver disease (NAFLD) and carbon tetrachloride (CCl 4 )-induced liver fibrosis, in rats. Methods In this experimental study, male rats were randomly divided into different experimental groups including: Experiment 1; group1: healthy rats received normal saline, 2: CCl 4 group, 3: CCl 4 + nanoparticle. Experiment 2; group1: healthy rats received chow diet, 2: NAFLD group, 3: NAFLD + nanoparticle. The oxidative stress markers were determined in the liver and intestine. Tumor necrosis factor-α (TNF-α) levels were measured by ELISA. Histopathological changes of liver and intestine were evaluated by light microspore. Results Total antioxidant capacity (TAC) and glutathione (GSH) levels significantly decreased, while malondialdehyde (MDA) and total oxidant status (TOS) were significantly increased in the liver, and intestine of the NAFLD and CCl 4 group compared with control rats. However, the use of nanoparticles significantly normalized these markers. The levels of the TNF-α were significantly reduced in the nanoparticle group as compared with NAFLD model and CCl 4 -treated rats. CeO 2 NPs also normalized the liver and intestinal histological changes. Conclusions Our finding revealed that CeO 2 NPs has potential protective effects by increasing antioxidant activity, and reducing inflammation.