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Review 1: "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 1: "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: This paper provides minimal useful information. It uses descriptive and simple statistics to study adverse events of COVID-19 vaccines using passive surveillance system, VAERS. This paper acknowledges the limitations of VAERS. However, the methods they used are not rigorous. First, the paper uses VAERS reports from 01/01/2020 to 08/20/2021 to compare COVID-19 and Flu vaccines. However, subjects who got Flu vaccines during this time were likely received COVID-19 vaccine as well. It is hard to link the reported adverse event to the appropriate vaccine if it is observed after both. It is better to use VAERS reports of the Flu vaccines before COVID-19 vaccines become available. It is also not a good strategy to study most frequently reported adverse events. For example, fever is a common adverse event associated with COVID-19 vaccines, but it also strongly associated with Flu vaccines. Studying frequently reported adverse events might miss important safety signals. Another big concern is that they did a lot of comparisons (for multiple COVID-19 vaccines, 1st and 2nd doses, and different age groups). Given the huge number of comparisons, there is not an approach to appropriately adjust for multiple comparisons and the false discovery rate, leading to potentially many misleading significant findings. Some information is redundant. Since only Pfizer vaccine is given to age 12 group, there is no point to compare the report numbers for this group between COVID-19 vaccines. There is also lack of details on the Flu vaccines. There are different types of Flu vaccines, it is not clear which type(s) are used for the comparison.

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