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Authors: Clementi P et al.

Link to paper:

Journal/ Pre-Print: BioRxiv

Key Words: SARS-CoV-2, Hydroxychloroquine, Vero E6 cells, anti-SARS-CoV2 activity


1. This study suggestsed that continuous treatment (before and after SARS-CoV2 infection) with hydroxychloroquine has a maximum efficacy to inhibit the cytopathic effect activity in Vero E6 cells compared to treatment only before or after infection.


Main findings of the study

HCQ was effective in full-time treatment at 37°C and 4°C adsorption temperatures; little effect was observed if cells were only treated after infection regardless of the adsorption temperature; in post-adsorption treatment, HCQ showed an effect only when the adsorption was done at 4°C. Evidence was a combinationllection of cytopathic effects observation and RT-PCR analysis. Experiments done at the condition of 4°C and with Bafilomycin A1 served as a control.

· Does the paper increase our understanding of COVID19?

No.While the current study is in line with previous literature it does not add more except for the fact that Hydroxychloroquine has anti-viral activity using clinical isolates (hCoV-19/Italy/UniSR1/2020 (GISAID accession ID: EPI_ISL_413489).

· How does the study add to current knowledge?

Continuous treatment with Hydroxychloroquine has maximum anti-viral activity.


Understand the virology and/or cell biology of SARS-CoV2/COVID19:

Study shows anti-viral activity of Hydroxychloroquine on clinical isolates (hCoV-19/Italy/UniSR1/2020 (GISAID accession ID: EPI_ISL_413489) in an in-vitro setting using bright field microscopy and qPCR.

Treat of SARS-CoV2/COVID19 positive individuals:

If there are more robust data were collected from isolated patient cells or from animal models, findings in this study about the continuous treatment (before and after SARS-CoV2 infection) might contribute to the clinical strategy of treating COVID-19.


· In vitro study


Novelty: This study do not add much to the existing literature on anti-viral activity of Hydroxychloroquine except for the fact it was done on clinical isolate (mentioned below). This study compared the effect of HCQ with different types of treatment.

Standing in the field: Results not controversial but do lack robust study design and validation experiments. Multiple reports supports anti-viral activity of HCQ. The effectiveness of HCQ in

clinical use has been controverscial and data in this paper showed no effect when the HCQ was used only after the infection.

Appropriate statistics: N numbers are missing from the experiments.

Viral model used: Clinical isolate (hCoV-19/Italy/UniSR1/2020 (GISAID accession ID: EPI_ISL_413489)

Translatability: The study was performed in-vitro on Vero E6 cells. Study design and experimental proofs supporting authors claims is not robust enough to comment anything on translatability.

Main limitations:

1. No quantification of microscopy images or live/dead staining to confirm authors claim.

2. N number for the experiments (Fig. 1 and Fig. 3) are missing (difficult to comment how robust experiments are.

3. Positive control Bafilomycin treatment data not shown in the full and post-infection setting.

4. Data about no drug-related cytotoxic effect on uninfected cells were not shown.

The evidence of the effectiveness of HCQ is only tested at the cellular level, in vivo data is missing (?)