SARS-Cov-2 Infection versus Vaccine-Induced Immunity among Veterans

  1. Yinong Young-Xu
  2. Jeremy Smith
  3. Caroline Korves

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Abstract

Background

With over 40 million cases of SARS-CoV-2 infection reported in the US and discussion of both vaccine mandates as well as boosters ongoing, we aim to examine protection conferred by previous infection compared with vaccination so that citizens and policy makers can make informed decisions.

Objectives

To compare mRNA COVID-19 vaccine-induced immunity against immunity induced by previous infection with SARS-CoV-2 between June and August 2021 when the Delta variant became dominant in the US.

We conducted a retrospective observational study comparing two groups whose incident vaccination or infection occurred within the first two months of 2021: (1) SARS-CoV-2-naive individuals who received a full mRNA vaccination - 2 doses of either Pfizer or Moderna vaccine, (2) newly infected individuals who were subdivided into those have not been vaccinated and those have been vaccinated after their infection. Matched multivariable Cox proportional hazards model was applied. We evaluated laboratory (RT-PCR) confirmed SARS-CoV-2 infection during follow-up, COVID-related hospitalization, and deaths.

Setting

Veterans Health Administration (VHA).

Main outcomes

Positive SARS-CoV-2 PCR test, COVID-related hospitalization, and deaths. Protection was estimated from hazard ratios with 95% confidence intervals (CI).

Results

A total of 9,539 patients with SARS-CoV-2 infection during the first two months of 2021 were matched to 14,458 and 23,105 patients fully vaccinated with Moderna and Pfizer mRNA vaccines, during the same two months. 3,917 (41%) of patients with SARS-CoV-2 infection were subsequently vaccinated. We plan to study this group separately. Consequently, protections were estimated among those with infection but were not subsequently vaccinated and those vaccinated with a mRNA vaccine. Among seniors, Moderna and Pfizer mRNA vaccines offered stronger protection against infection, lowering the risk by an additional 66% [HR: 0.34 (95% CI, 0.14-0.78)] and 68% [HR: 0.32 (95% CI, 0.14-0.70)]; stronger protection against hospitalization, lowering the risk by an additional 61% [HR: 0.34 (95% CI, 0.14-0.78)] and 45% [HR: 0.34 (95% CI, 0.14-0.78)]; and stronger protection against deaths lowering the risk by an additional 95% [HR: 0.05 (95% CI, 0.004-0.62)] and 99% [HR: 0.01 (95% CI, 0.001-0.44)]. Among young adults (age < 65), the protections offered by vaccines were statistically equivalent to that provided by previous infection, especially in terms of absolute incidence rate.

Conclusions

Among the elderly (age 65 or older), two-dose mRNA vaccines provided stronger protection against infection, hospitalization, and death, compared to natural immunity. Among young adults (age < 65), the protections offered between natural immunity and vaccine-induced immunity were similar.

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  1. ScreenIT

    SciScore for 10.1101/2021.09.27.21264194: (What is this?)

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

    Table 1: Rigor

    EthicsIRB: The study protocol was approved by the institutional review board of the VA Medical Center in White River Junction, VT and was granted a waiver of consent.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    Data and baseline characteristics were constructed using SAS 9.4 (SAS Institute, Cary, North Carolina).
    SAS Institute
    suggested: (Statistical Analysis System, RRID:SCR_008567)
    Modeling was performed using Stata 17 (StataCorp, College Station, Texas).
    StataCorp
    suggested: (Stata, RRID:SCR_012763)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    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 10.1101/2021.09.27.21264194v1 on medRxiv