Effectiveness of vaccination against SARS-CoV-2 infection and Covid-19 hospitalisation among Finnish elderly and chronically ill—An interim analysis of a nationwide cohort study

  1. Ulrike Baum
  2. Eero Poukka
  3. Arto A. Palmu
  4. Heini Salo
  5. Toni O. Lehtonen
  6. Tuija Leino

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Abstract

In Finland, both mRNA and adenovirus vector (AdV) Covid-19 vaccines have been used after the vaccination campaign started on December 27, 2020. Vaccination of the elderly and chronically ill was prioritized and the interval between doses set to 12 weeks. The objective of this interim analysis was to evaluate first and second dose vaccine effectiveness (VE) in a real-world setting.

Methods

During the first five months of the campaign, a register-based cohort study was conducted in the Finnish elderly aged 70+ years and those aged 16–69 years with medical conditions predisposing to severe Covid-19 (chronically ill). Using Cox regression, VE against SARS-CoV-2 infection and Covid-19 hospitalisation was estimated comparing the hazard in the vaccinated with that in the unvaccinated.

Results

The cohorts included 901092 elderly (89% vaccinated) and 774526 chronically ill (69% vaccinated) individuals. Three weeks after the first dose, mRNA VE against infection was 45% (95% confidence interval, 36–53%) and 40% (26–51%) in elderly and chronically ill; mRNA VE against hospitalisation was 63% (49–74%) and 82% (56–93%). In chronically ill, AdV VE was 42% (32–50) and 62% (42–75%) against infection and hospitalisation, respectively. One week after the second dose, mRNA VE against infection was 75% (65–82%) and 77% (65–85%) in elderly and chronically ill; mRNA VE against hospitalisation was 93% (70–98%) and 90% (29–99%).

Conclusions

Covid-19 vaccines protect against SARS-CoV-2 infection and Covid-19 hospitalisation. A single dose provides moderate protection in elderly and chronically ill, although two doses are clearly superior.

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  1. Version published to 10.1371/journal.pone.0258704
  2. ScreenIT

    SciScore for 10.1101/2021.06.21.21258686: (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

    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:
    A limitation of this study is the unknown proportion of asymptomatic cases among the confirmed infections. As VE is greater when measured against a more severe outcome [8], the proportion of asymptomatic cases strongly influences the VE estimates. The major weakness is, however, the presence of time-limited selection bias as in [13]. At the day of vaccination, vaccinees were healthier than average due to the policy to postpone the vaccination of individuals with acute symptoms suggestive of Covid-19 and those in self-isolation. Consequently, the hazards of infection and hospitalization in the recently vaccinated were lower than the hazards in the unvaccinated. In the absence of any bias, these hazards should have been similar in the vaccinated and unvaccinated as it takes 2–3 weeks for the vaccine-induced immune response to develop. In addition, residual confounding may be present due to the observational nature of the study.

    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 10.1101/2021.06.21.21258686 on medRxiv