Vaccine effectiveness against referral to hospital after SARS-CoV-2 infection in St. Petersburg, Russia, during the Delta variant surge: a test-negative case-control study

  1. Anton Barchuk
  2. Mikhail Cherkashin
  3. Anna Bulina
  4. Natalia Berezina
  5. Tatyana Rakova
  6. Darya Kuplevatskaya
  7. Oksana Stanevich
  8. Dmitriy Skougarevskiy
  9. Artemiy Okhotin

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Abstract

Background

The results of a randomised trial showed the safety and efficacy of Gam-COVID-Vac against COVID-19. However, compared to other vaccines used across the globe, the real-world data on the effectiveness of Gam-COVID-Vac, especially against the disease caused by the Delta variant of concern, was limited. We aimed to assess the effectiveness of vaccination mainly conducted with Gam-COVID-Vac in St. Petersburg, Russia.

Methods

We designed a case-control study to assess the vaccine effectiveness (VE) against referral to hospital. Self-reported vaccination status was collected for individuals with confirmed SARS-CoV-2 infection who were referred for initial low-dose computed tomography (LDCT) triage in two outpatient centres in July 3–August 9, 2021, in St. Petersburg, Russia. We used logistic regression models to estimate the adjusted (for age, sex, and triage centre) VE for complete (14 days or more after the second dose) vaccination. We estimated the VE against referral for hospital admission, COVID-19-related lung injury assessed with LDCT, and decline in oxygen saturation.

Results

In the final analysis, 13,893 patients were included, 1291 (9.3%) patients met our criteria for complete vaccination status, and 495 (3.6%) were referred to hospital. In the primary analysis, the adjusted VE against referral to hospital was 81% (95% confidence interval: 68–88) for complete vaccination. The VE against referral to hospital was more pronounced in women (84%, 95% CI: 66–92) compared to men (76%, 95% CI: 51–88). Vaccine protective effect increased with increasing lung injury categories, from 54% (95% CI: 48–60) against any sign of lung injury to 76% (95% CI: 59–86) against more than 50% lung involvement. A sharp increase was observed in the probability of hospital admission with age for non-vaccinated patients in relation to an almost flat relationship for the completely vaccinated group.

Conclusions

COVID-19 vaccination was effective against referral to hospital in patients with symptomatic SARS-CoV-2 infection in St. Petersburg, Russia. This protection is probably mediated through VE against lung injury associated with COVID-19.

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  1. Version published to 10.1186/s12916-022-02509-8
  2. ScreenIT

    SciScore for 10.1101/2021.08.18.21262065: (What is this?)

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

    Table 1: Rigor

    EthicsIRB: Ethical considerations: The Ethics Committee of the MIBS approved the study on June 21, 2020.
    Consent: All participants signed the informed consent upon referral to the LDCT triage.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power AnalysisOur sample size of 495 hospitalized patients (cases), 13,399 non-hospitalized patients (controls), and 1,291 patients with the complete vaccination status (exposure level of 9.3%) provides 80% power to detect an odds ratio of 0.58 (or the VE of 42%) and 1.46 (or the VE of -46%) for hospitalization at the 5% alpha level in our unmatched case-control study.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: Thank you for sharing your code and data.

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    There are several important limitations of our study. We did not have the information on the vaccine type, so the estimated VE represent an average effect of vaccination in St. Petersburg. However, according to official statistics, by July 23, 2021, in St. Petersburg, among 1,227,496 individuals who received at least one vaccine dose, 1,178,266 or 96% received Gam-COVID-Vac, and the rest is distributed between the other two vaccines (EpiVacCorona — 21,943 or 1.7% and KoviVac 27,287 or 2.2%) [19]. It is safe to assume that our study approximates the effectiveness of Gam-COVID-Vac. The effectiveness for EpiVacCorona and KoviVac would be difficult to derive from observational case-control studies due to negligible uptake. Another important limitation of our study is possible referral bias. Patients were referred to the triage centres if they had positive PCR tests and disease symptoms, but the decision to refer was left at the physician’s discretion. We cannot rule out that the vaccination status was influencing this decision. If this is the case, in our data we would observe more severely ill vaccinated individuals than the unvaccinated ones. Alternatively, the physicians may fully rely on vaccine protection and never refer the vaccinated patients to the triage. However, we observed a considerable number of vaccinated individuals at the triage centres. Therefore, we believe that the referral bias would result in underestimation of the VE. Vaccination could also influence patien...

    Results from TrialIdentifier: We found the following clinical trial numbers in your paper:

    IdentifierStatusTitle
    NCT04981405Active, not recruitingReal-world Evidence of COVID-19 Vaccines Effectiveness

    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.

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  3. Version published to 10.1101/2021.08.18.21262065 on medRxiv