Effectiveness of Vaccination against SARS-CoV-2 Infection in the Pre-Delta Era: A Systematic Review and Meta-Analysis

  1. Angela Meggiolaro
  2. Monica Sane Schepisi
  3. Georgios F. Nikolaidis
  4. Daniele Mipatrini
  5. Andrea Siddu
  6. Giovanni Rezza

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Abstract

(1) Background: The objective of this study was to assess the effectiveness of SARS-CoV-2 vaccines in terms of prevention of disease and transmission in the pre-Delta era. The evaluation was narrowed to two mRNA vaccines and two modified adenovirus-vectored vaccines. (2) Methods: The overall risk of any SARS-CoV-2 infection confirmed by positive real-time Polymerase Chain Reaction (PCR) test was estimated in partially and fully vaccinated individuals. The evidence synthesis was pursued through a random-effects meta-analysis. The effect size was expressed as relative risk (RR) and RRR (RR reduction) of SARS-CoV-2 infection following vaccination. Heterogeneity was investigated through a between-study heterogeneity analysis and a subgroup meta-analysis. (3) Results: The systematic review identified 27 studies eligible for the quantitative synthesis. Partially vaccinated individuals presented a RRR = 73% (95%CI = 59–83%) for positive SARS-CoV-2 PCR (RR = 0.27) and a RRR=79% (95%CI = 30–93%) for symptomatic SARS-CoV-2 PCR (RR = 0.21). Fully vaccinated individuals showed a RRR = 94% (95%CI = 88–98%) for SARS-CoV-2 positive PCR (RR = 0.06) compared to unvaccinated individuals. The full BNT162b2 vaccination protocol achieved a RRR = 84–94% against any SARS-CoV-2-positive PCR and a RRR = 68–84% against symptomatic positive PCR. (4) Conclusions: The meta-analysis results suggest that full vaccination might block transmission. In particular, the risk of SARS-CoV-2 infection appeared higher for non-B.1.1.7 variants and individuals aged ≥69 years. Considering the high level of heterogeneity, these findings must be taken with caution. Further research on SARS-CoV-2 vaccine effectiveness against emerging SARS-CoV-2 variants is encouraged.

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  1. Version published to 10.3390/vaccines10020157
  2. ScreenIT

    SciScore for 10.1101/2021.08.25.21262529: (What is this?)

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

    Table 1: Rigor

    Ethicsnot detected.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    We used seven different web engines, including early stage research platforms: Pubmed, Cochrane, clinicaltrial.gov, and COVID-NMA, medRxiv, SSRN, and Authorea.
    Pubmed
    suggested: (PubMed, RRID:SCR_004846)
    Cochrane
    suggested: (Cochrane Library, RRID:SCR_013000)
    Authorea
    suggested: (Authorea, RRID:SCR_002547)

    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: We detected the following sentences addressing limitations in the study:
    This systematic review acknowledged several limitations. Undeniably, the expected heterogeneity stemmed from the observational design of the included studies. Unless a randomized process, it is unlikely to be reduced in any circumstances. Moreover, several studies lacked of data on population characteristics. For instance, the meta-analysis predominantly included Caucasian populations whereas vaccines may have different effectiveness across individuals from different ethnicities. Moreover, five studies did not declare to test systematically the vaccinated cohort during the follow-up. The absence of active laboratory surveillance within vaccinated individuals might have resulted in an underestimation of asymptomatic cases. However, we did not consider a different rate of testing as a bias of concern in terms of RR estimate, because both vaccinated and unvaccinated individuals underwent the same case investigation and contact tracing protocol. Moreover, when systematic testing was not performed, asymptomatic testing was available to different extent: workplace exposures (HCWs), out-of-state travellers or per-request.[37] In general, SARS-CoV-2 PCR testing was highly accessible and free of charge.[11, 50] However, asymptomatic cases which progressed into symptomatic disease could act as source of bias in both vaccinated and unvaccinated groups.[37, 43] Finally, public health mitigation measures might contribute to the underestimation of SARS-CoV-2 vaccine effectiveness. Unfortun...

    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

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  3. Version published to 10.1101/2021.08.25.21262529 on medRxiv