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Introduction Our objective was to describe and compare self-reported side effects of COVID-19 vaccines in the USA.

Methods A web-based registry enrolled volunteers who received a COVID-19 vaccine between March 19 –July 15, 2021. We collected self-reported short-term side effects, medical consultation, hospitalization, and quality of life impact following completed vaccination regimens (Pfizer, Moderna, J&J).

Results We recruited 6,966 volunteers who completed their full course of vaccination (median age 48 years, IQR 35.0-62.0; 83.6% female): Pfizer 3,486; Moderna 2,857; J&J 623. Few (3.1%) sought medical care for post-vaccination side effects. Hospitalization (n=17; 0.3%) and severe allergic reactions (n=39; 0.6%) also were rare. Those with autoimmune disease or lung disease were approximately twice as likely to seek medical care (adjusted odds ratio (aOR) 2.01 [95% CI: 1.39;2.92] and 1.70 [95% CI: 1.12;2.58] respectively). 92.4% of participants reported ≥1 side effect (median 3), with injection site reactions (78.9%), fatigue (70.3%), headache (49.0%) reported most frequently. More side effects were reported after the second dose of two-dose vaccines (medians: 1 vs. 2 for Pfizer and 1 vs. 3 for Moderna for first and second doses respectively) versus 3 for J&J’s single-dose vaccine. For the employed, the median number of workdays missed was one. Diabetics and those vaccinated against influenza were substantially less likely to report ≥3 symptoms (aOR 0.68, 95% CI 0.56,0.82 and aOR 0.82, 95% CI 0.73,0.93, respectively.)

Discussion The total side effect burden was, not unexpectedly, greater with two-dose regimens but all three vaccines appear relatively safe. Very few subjects reported side effects serious enough to warrant medical care or reported post-vaccination hospitalization. While these findings do not address possible long-term effects, they do inform on their short-term safety and tolerability and will hopefully provide some reassurance and positively inform the benefit-risk and pharmacoeconomic assessment for all three vaccines. NCT04368065

Competing Interest Statement

The authors have declared no competing interest.

Clinical Protocols

Funding Statement

This work was supported in part by a contract with the US Food and Drug Administration. The bulk of the funding was provided by IQVIA.

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.


The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Advarra Inc is the ethics committee that has reviewed and approved our protocol

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.


I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).


I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.



  • Authors’ email addresses: Nancy.Dreyer{at}IQVIA.comMatthew.Reynolds{at}IQVIA.comLisa.Albert{at}IQVIA.comEmma.Brinkley{at}IQVIA.comTom.Kwon{at}IQVIA.comChristina.Mack{at}IQVIA.comMalaria{at} [Stephen Toovey]

Paper in collection COVID-19 SARS-CoV-2 preprints from medRxiv and bioRxiv

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