Effectiveness of mRNA COVID-19 Vaccines among Employees in an American Healthcare System

  1. Nabin K. Shrestha
  2. Amy S. Nowacki
  3. Patrick C. Burke
  4. Paul Terpeluk
  5. Steven M. Gordon

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Abstract

Background

The mRNA SARS-CoV-2 vaccines have shown great promise in clinical trials. The purpose of this study was to evaluate the effectiveness of these vaccines under real-world conditions in the USA.

Methods

Employees of the Cleveland Clinic Health System, previously not infected with SARS-CoV-2, and working in Ohio on Dec 16, 2020, the day COVID-19 vaccination began, were included. The cumulative incidence of SARS-CoV-2 infection, over the next 5 months, was compared among those who received the vaccine and those who did not, by modeling vaccination as a time-dependent covariate in Cox proportional hazards regression analyses adjusted for the slope of the epidemic curve as a continuous time-dependent covariate.

Results

Of the 46866 included employees, 28223 (60%) were vaccinated by the end of the study period. The cumulative incidence of SARS-CoV-2 infection was much higher among those not vaccinated than those vaccinated. Only 15 (0.7%) of the 2154 SARS-CoV-2 infections during the study occurred among those vaccinated. After adjusting for the slope of the epidemic curve, age, and job type, vaccination was associated with a significantly reduced risk of SARS-CoV-2 infection (HR 0.03, 95% C.I. 0.02 – 0.06, p < 0.001), corresponding to a vaccine effectiveness rate of 97.1% (95% CI 94.3 – 98.5). Vaccine effectiveness was 89.2% at 7 days and 95.0% at 14 days after the first vaccine dose.

Conclusions

The mRNA SARS-CoV-2 vaccines are over 97% protective against COVID-19 in the working-age population, with substantial protection possibly apparent within a few days of the first dose.

Summary

The effectiveness of mRNA SARS-CoV-2 vaccines was evaluated among 46866 employees in an American healthcare system. After adjusting for age, job type, and the phase of the epidemic, vaccination was 97.1% effective in preventing COVID-19 among the fully vaccinated, and 89.2% protective within 7 days of the first dose.

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  1. ScreenIT

    SciScore for 10.1101/2021.06.02.21258231: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: The study was approved by the Cleveland Clinic Institutional Review Board (IRB no. 21-300).
    Consent: A waiver of informed consent and waiver of HIPAA authorization were approved to allow access to PHI by the research team, with the understanding that sharing or releasing identifiable data to anyone other than the study team was not permitted without additional IRB approval.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: Thank you for sharing your data.

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    A limitation of our study is that the absence of a program of systematic testing of asymptomatic individuals would have resulted in most asymptomatic infections being missed. This study therefore cannot exclude the possibility that asymptomatic infections might have occurred despite vaccination. This is not a crippling limitation, however, as asymptomatic patients would have been missed in both the unvaccinated and vaccinated groups. It is also theoretically possible that vaccinated persons were less likely to be tested than unvaccinated ones when suspicious symptoms arose. This is probably less of a limitation among our HCP than it might have been in other populations because of easy access to testing (no co-payment required and streamlined testing process for HCP), and the expectation of HCP being exposed to the disease during the course of their work, which would have increased the likelihood of testing for COVID-19 if suspicious symptoms arose. Certain groups were not represented in our study, including children and the elderly, and the number of immunocompromised patients would have been expected to have been small. Caution is advised in in extrapolating the findings of the study to these groups. Our study’s findings add to the growing literature on the effectiveness of the mRNA SARS-CoV-2 vaccines. These findings are consistent with other studies that have examined this question using different approaches at different sites in the USA [5,6,11]. The high rates of vaccine...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2021.06.02.21258231v1 on medRxiv