Objective: The receptor-binding domain (RBD) of the S1 domain of the SARS-CoV- 2 Spike protein performs a key role in the interaction with Angiotensin-converting enzyme 2 (ACE2), leading to both subsequent S2 domain-mediated membrane fusion and incorporation of viral RNA in host cells. Methods: In this study, we investigated the inhibitor’s targeted compounds through existing human ACE2 drugs to use as a future viral invasion. 54 FDA approved drugs were selected to assess their binding affinity to the ACE2 receptor. The structurebased methods via computational ones have been used for virtual screening of the best drugs from the drug database. Key Findings: The ligands “Cinacalcet” and “Levomefolic acid” highaffinity scores can be a potential drug preventing Spike protein of SARS-CoV-2 and human ACE2 interaction. Levomefolic acid from vitamin B family was proved to be a potential drug as a spike protein inhibitor in previous clinical and computational studies. Besides that, in this study, the capability of Levomefolic acid to avoid ACE2 and Spike protein of SARS-CoV-2 interaction is indicated. Therefore, it is worth to consider this drug for more in vitro investigations as ACE2 and Spike protein inhibition candidate. Conclusion: The two Cinacalcet and Levomefolic acid are the two ligands that have highest energy binding for human ACE2 blocking among 54 FDA approved drugs.

Considering the fact that vaccine efficacy may be a difficult concept for physicians and health officials alike, we decided to explain it using data from the first publication on the efficacy and safety of a COVID-19 vaccine produced by Pfizer/BioNTech. We examined the published data and calculated common epidemiological parameters such as RRR (relative risk reduction), RR (relative risk), ARR (absolute risk reduction) and NNT (number needed to treat) for 3 groups of patients as described in the original paper. Further, we calculated safety parameters for the vaccine as NNH (number needed to harm) for any, related and severe side effects as mentioned by the investigators. We argue that both NNT and NNH are necessary estimates of how a vaccine might perform in real life and that a robust understanding of efficacy is vital for patients and health care providers as well as health officials in order to make responsible and balanced policy decisions regarding vaccination.