COVID-19 vaccine effectiveness against symptomatic SARS-CoV-2 infections, COVID-19 related hospitalizations and deaths, among individuals aged ≥65 years in Portugal: A cohort study based on data-linkage of national registries February-September 2021

  1. Ausenda Machado
  2. Irina Kislaya
  3. Ana Paula Rodrigues
  4. Duarte Sequeira
  5. João Lima
  6. Camila Cruz
  7. Pedro Pinto Leite
  8. Carlos Matias Dias
  9. Baltazar Nunes

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Abstract

Using data from electronic health registries, this study intended to estimate the COVID-19 vaccine effectiveness (VE) in the population aged 65 years and more, against symptomatic infection, COVID-19-related hospitalizations, and deaths, overall and by time since complete vaccination for the period February to September 2021

Methods

We established a cohort of individuals aged 65 and more years old, resident in Portugal mainland, using the National Health Service User number to link eight electronic health registries. Outcomes included were symptomatic SARS-CoV-2 infections, COVID-19-related hospitalizations or deaths. The exposures of interest were the mRNA vaccines (Comirnaty or Spikevax) and the viral vector (Vaxzevria) vaccine. Complete schedule VE was estimated as one minus the confounder adjusted hazard ratio, for each outcome, estimated by time-dependent Cox regression with time-dependent vaccine exposure.

Results

For the cohort of individuals aged 65–79 years, complete scheme VE against symptomatic infection varied 43 (95%CI: 37–49) (Vaxzevria) and 65 (95%CI: 62–68) (mRNA vaccines). This estimate was slightly lower in the ≥80 years cohort (53, 95%CI: 45–60) for mRNA vaccines). VE against COVID-19 hospitalization varied between 89% (95%CI: 52–94) for Vaxzevria and 95% (95%CI: 93–97) for mRNA vaccines for the cohort aged 65–79 years and was 76% (95%CI: 67–83) for mRNA vaccines in the ≥80 years cohort. High VE against COVID-19-related deaths was estimated, for both vaccine types, 95% and 81 (95%CI:76–86) for the 65–79 years and the ≥80 years cohort, respectively. We observed a significant waning of VE against symptomatic infection, with VE estimates reaching approximately 34% for both vaccine types and cohorts. Significant waning was observed for the COVID-19 hospitalizations in the ≥80 years cohort (decay from 83% (95%CI:68 to 91) 14–41 days to 63% (95%CI:37 to 78) 124 days after mRNA second dose). No significant waning effect was observed for COVID-19-related deaths in the period of follow-up of either cohort.

Conclusions

In a population with a high risk of SARS-CoV-2 complications, we observed higher overall VE estimates against more severe outcomes for both age cohorts when compared to symptomatic infections. Considering the analysis of VE according to time since complete vaccination, the results showed a waning effect for both age cohorts in symptomatic infection and COVID-19 hospitalization for the 80 and more years cohort.

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  1. Version published to 10.1371/journal.pone.0274008
  2. ScreenIT

    SciScore for 10.1101/2021.12.10.21267619: (What is this?)

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

    Table 1: Rigor

    EthicsIRB: Ethical considerations: The study protocol was approved by the Ethical Committee of the Instituto Nacional de Saúde Doutor Ricardo Jorge (INSA) and the data protection officers of INSA, General Directorate for Health, ACSS and SPMS.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    No key resources detected.

    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:
    The present study has some limitations, namely related to the datasets used and their quality. For instance, the main dataset used to link data was the NHSU, which contains the unique health number attributed to each individual residing in Portugal. However, as referred, the NHSU database could have update issues, and occasional and temporary registrations of NHS users, such as immigrants and asylum seekers, that could artificially increase the number of individuals in a given cohort. To overcome this limitation, several restriction criteria were included, and from the initial extraction a total of 1,178,975 registries were excluded from the analysis. Final cohort age and sex distribution were comparable to National Statistics estimates for individuals aged 65 and more years [31]. In terms of prevalence of chronic conditions, final cohorts were also comparable to National estimates (INS 2019). Another potential limitation is related to information bias. In Portugal, during the study period, testing guidelines were not different for vaccinated and non-vaccinated individuals which may have differentially limited the opportunity of infection ascertainment in vaccinated and unvaccinated. Nevertheless, we cannot rule out the hypothesis that vaccinated individuals could have had a differential (due to acceptance) testing performance if asymptomatic or if they had any contact with COVID-19 case. Under this hypothesis there is a potential bias due to different infection ascertainment...

    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.

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  3. Version published to 10.1101/2021.12.10.21267619v1 on medRxiv