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Review 2: "Comparison of adverse events between COVID-19 and Flu Vaccines"

Preprint presents analysis of COVID-19 & flu vaccine-related adverse events using VAERS. Reviewers found results potentially informative in showing effects of the vaccines, but there are limitations to the dataset, the study has flawed methods, and findings are not actionable.

Published onOct 21, 2021
Review 2: "Comparison of adverse events between COVID-19 and Flu Vaccines"
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key-enterThis Pub is a Review of
Comparison of adverse events between COVID-19 and Flu vaccines

ABSTRACTBACKGROUNDAmong the various driving factors for vaccine hesitancy, confidence in the safety associated with the vaccine constitutes as one of the key factors. This study aimed at comparing the adverse effects of COVID-19 vaccines with the Flu vaccines.METHODSThe VAERS data from 01/01/2020 to 08/20/2021 were used. The MedDRA terms coded by VAERS were further aggregated by a clinician into clinically meaningful broader terms.RESULTSVarious common adverse events between Flu and COVID-19 vaccines have been identified. Adverse events such as headache and fever were very common across all age groups. Among the common adverse events between Flu and COVID-19 vaccine, the relative risk along with 95% CI indicated that such common adverse events were more likely to be experienced by COVID-19 vaccine users than Flu vaccine users. Our study also quantified the proportion of rare adverse events such as Guillain Barre Syndrome and Gynecological changes in the VAERS database for COVID-19 vaccines.CONCLUSIONSBased on the available data and results, it appears that there were some common adverse events between Flu vaccines and COVID-19 vaccines. These identified common adverse events warrant further investigations based on the relative risk and 95% CI.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.


Review: Pradhan et al. performed a descriptive analysis of COVID-19 and flu vaccine related adverse events using VAERS data. The research is timely and important. The authors note that there is similarity in the types of adverse events reported when the top 10 adverse events are looked at. The study findings may provide a basis for more focused studies in this area. Some of the issues of concern regarding this research which need to be considered are stated below:

  1. Presence of duplicate reports in the VAERS database can affect the analysis outcome. Given the scientific community and public attention towards COVID vaccine safety, there is a higher chance of the same report being reported by different sources. If no deduplication measures have been used, this needs to be highlighted as a study limitation.

  2. In Results, the authors use the phrase “more likely to experience” even when the RR and CI suggest a lesser risk. For example, “persons receiving first dose of Pfizer vaccine were 0.64 times more likely to experience pallor (95% CI: 0.44 to 0.95)”.

  3. The Discussion is too brief and does not adequately describe the key differences or similarities in the AEs reported with the two vaccines. Since the authors intended the study findings to help address the issue of vaccine hesitancy, a clear articulation of the study findings is necessary. The statement “it appears that there were some common adverse events between Flu vaccines and COVID-19 vaccines” in Conclusion seems vague and may not be easily interpretable/actionable.

  4. The authors state that rare AEs are difficult to detect. However, the current study was not designed to assess rare AEs since the analysis was confined to the top 10 AEs. One of the advantages of using VAERS data is to identify uncommon AEs and their potential relationship with use of a particular vaccine, although, as the authors rightly state, such studies need to be confirmed by further studies.

  5. The authors mention regarding “lack of availability of time to each adverse event” in the study limitations. However, VAERS does contain ‘onset interval’ as a variable although the data may be missing in many reports.

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