COVID-19 vaccine effectiveness among healthcare workers in Portugal: results from a hospital-based cohort study, December 2020 to November 2021

  1. Vânia Gaio
  2. Adriana Silva
  3. Palmira Amaral
  4. João Faro Viana
  5. Pedro Pinto Leite
  6. Carlos Matias Dias
  7. Irina Kislaya
  8. Baltazar Nunes
  9. Ausenda Machado

Reviewed by

Read the full article See related articles

Listed in

Log in to save this article

Abstract

Introduction

Healthcare workers (HCW) were amongst the first prioritized for COVID-19 vaccination but data on COVID-19 vaccine effectiveness among HCW is still limited. This study aims to estimate the COVID-19 vaccine effectiveness (VE) against SARS-CoV-2 symptomatic infection among HCW from Portuguese hospitals.

Methods

In this prospective cohort study, we analysed data from HCW (all professional categories) from two central hospitals in the Lisbon and Tagus Valley and Centre regions of mainland Portugal between December 2020 and November 2021. VE against symptomatic SARS-CoV-2 infection was estimated as one minus the confounder adjusted hazard ratios by Cox models considering age group, sex, presence of chronic disease and occupational exposure to patients diagnosed with COVID-19 as adjustment variables.

Results

During the 11 months of follow up, the 2213 HCW contributed a total of 1950 person-years at risk and 171 SARS-CoV-2 events occurred. The COVID-19 incidence rate for unvaccinated HCW was 348.7 per 1000 person-years while for fully vaccinated HCW was 43.0 per 1000 person-years. We observed a VE against symptomatic SARS-CoV-2 infection of 73.9% (95% CI: 26.2–90.8%) for complete vaccination status.

Conclusion

This cohort study found a high COVID-19 VE against symptomatic SARS-CoV-2 infection in Portuguese HCW, which is in concordance with previous studies from other countries. Monitoring of VE in this HCW cohort continues during the winter 2021/2022 to evaluate potential VE decay and booster vaccine effect.

Article activity feed

  1. ScreenIT

    SciScore for 10.1101/2022.01.07.22268889: (What is this?)

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

    Table 1: Rigor

    EthicsConsent: After accepting to participate and signing a written consent, each HCW answered an enrolment questionnaire implemented in the REDcap platform (16).
    IRB: This study protocol was approved by the ethics committee of the Instituto Nacional de Saúde Doutor Ricardo Jorge (date of approval.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    Further, on a weekly basis, participants answered a follow-up questionnaire (through the REDcap platform) which included questions on symptoms and COVID-19 testing in the previous 7 days.
    REDcap
    suggested: (REDCap, RRID:SCR_003445)

    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:
    One of the limitations of our study is related to the sample size and small number of unvaccinated individuals. In fact, the relatively small sample size of the HCW cohort (n=2213), the high vaccine coverage and the few events observed during the study period contributed to the low precision of the estimates. Moreover, most of the events occurred in a restricted period of time while no events were observed in most of the follow-up weeks. However, the distribution of events over time was comparable to the epidemic curve observed in the Portuguese community aged between 18-70 years old for the same period (21). On the other hand, outcome measurement was conducted using the same informatics platform for all participant HCW, and so differential measurement of outcome is not plausible. In addition, this study did not include variables related with adherence to vaccination of other preventive behaviours and this may have resulted in residual confounding, as the three categories of vaccination status may be associated with those behaviours or according to other individual HCW characteristics that may be associated with either vaccination uptake or risk of infection. Larger cohort studies of HCW with long follow-up periods relied on weekly symptoms reporting, which result in a high burden for the participants and are difficult to maintain. One possible solution to obtain more robust vaccine effectiveness estimates in this risk group is to use cohorts based on electronic registries as...

    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 10.1101/2022.01.07.22268889v1 on medRxiv