Review for 10.1186/s12876-022-02507-3 (2022)

Title: New-onset and relapsed liver diseases following COVID-19 vaccination: A systematic
review
Version: 1 Date: 06 Aug 2022
Reviewer's report:
The authors of this manuscript try to present the evidence of liver injury/disease following
Covid-19 vaccination through systematic review and meta-analysis. I think the novelty and
significance of this manuscript is lacking, as the results from this manuscript did not add anything
new into the existing literature and did not have any implications for clinical practice. Moreover,
there are several major methodological flaws in this manuscript which reflect that the authors
were not fully understood about systematic review process. The presentation of results also a
little bit confusing and not clear enough. My detailed comments regarding this manuscript can
be seen below:
1) In the title, the authors have mentioned that this study is a systematic review and meta-analysis
study. However, in the Results section, I don't see any meta-analysis results. Please clarify and
explain. If this study did not involve meta-analysis, then don't state about meta-analysis in the
Title because it will cause confusion from the readers. If this study involve meta-analysis as
stated in the title, then please provide the Forest Plot and Funnel plot results.
2) I wonder what is the significance of this study? What does this study offer? How can the
results from this study affect the current practice or guidelines? Please clearly explain.
3) I think the background of this manuscript is not sufficient to explain the rationale to conduct
this study. Why we need to performed a systematic review on the liver injury after Covid-19
vaccination? If most of the included studies were only case report or case-series (as stated at the
end of Background section), it won't give us the clear picture about the incidence of liver injury
after Covid-19 vaccination because case report and case-series studies did not have comparison/
control group.
4) Has this study been registered on PROSPERO? If yes, please state the registration number.
If no, please explain the reasons.
5) Methods: "...2019 novel coronavirus PLUS vaccine OR vaccination..." In my personal
experience as researcher and reviewers, I never see the term "PLUS" as conjunction for search
strategy. The commonly used conjunctions are "OR" and "AND". Please explain or revise.
6) Methods: The inclusion and exclusion criteria were not described in details. Please use
PICOS formulation to give a better description of eligibility criteria. Moreover the term "liver
histopathology" here should be clearly explained. Histopathology often refer to microscopic
examination from a tissue specimen. Do all of the included studies should have microscopic
examination (histopathology) results? Is it liver hisopathology or liver disease? Please explain.
7) Methods: The process for selection of studies were also not described in details. Authors have
only mentioned about selecting the studies based on titles and abstracts. How about removal
of duplicates? How about full-text assessment? The process should conform to the PRISMA
guidelines.
8) Methods: I think the authors have incorrectly use the tool for quality assessment of included
studies. Newcastle Ottawa Scale (NOS) was not intended for case-report nor case-series studies,
but for cohort or case-control studies. Case report and most of case-series will not fulfill the
'comparability' assessment criteria from NOS. Moreover, the 'selection' criteria from NOS will
not be fitted for case report study as there is no selection of representative samples. Even though
the tool was not fitted, I still see the assessment results from NOS in the Table 1. How can this
happened? How can the authors assess those studies using NOS? I think this mistake is very fatal.
9) Methods: in the Data Analysis, the authors have mentioned about using Microsoft Excel for
the analysis. I think this is fatal. Meta-analysis can never be performed using Microsoft Excel.
There are several validated software to conduct meta-analysis, such as Review Manager, Stata,
R package, etc.
10) Results: In Figure 1, the authors did not describe the reasons for exclusion after full-text
assessment. If the full-texts were excluded, then the reasons for exclusion should be stated.
11) Results: The presentation of results is not clear and a little bit confusing.
12) The English quality of this manuscript should be improved.