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Open Forum Infect Dis
. 2024 Sep 19;11(10):ofae547.
doi: 10.1093/ofid/ofae547. eCollection 2024 Oct. Effectiveness of the First and Second Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine Dose: A Nationwide Cohort Study From Austria on Hybrid Versus Natural Immunity
Alena Chalupka 1 2 , Uwe Riedmann 1 , Lukas Richter 2 3 , Ali Chakeri 2 4 , Ziad El-Khatib 2 , Martin Sprenger 5 , Verena Theiler-Schwetz 1 , Christian Trummer 1 , Peter Willeit 6 7 8 , Harald Schennach 9 , Bernhard Benka 2 , Dirk Werber 2 , Tracy Beth Høeg 10 11 , John P A Ioannidis 12 , Stefan Pilz 1
Affiliations
Background: We aimed to evaluate the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinations in previously SARS-CoV-2-infected adults in the general population of Austria during the Delta wave and with extended follow-up.
Methods: In a nationwide retrospective cohort study, we calculated age-, sex-, and nursing home residency-adjusted Cox proportional hazard ratios (HRs) of coronavirus disease 2019 (COVID-19) deaths, SARS-CoV-2 infections, and non-COVID-19 deaths from 1 October to 31 December 2021, and secondarily with extended follow-up to 30 June 2022. Relative vaccine effectiveness (rVE) is rVE = (1 - HR) × 100.
Results: Among 494 646 previously infected adults, 169 543 had received 2 vaccine doses, 133 567 had received 1 dose, and 190 275 were unvaccinated at baseline. We recorded 17 COVID-19 deaths (6 vaccinated, 11 unvaccinated) and 8209 SARS-CoV-2 infections. Absolute risk of COVID-19 deaths was 0.003%. rVE estimates for COVID-19 deaths and reinfections exceeded 75% until the end of 2021 but decreased substantially with extended follow-up. The risk of non-COVID-19 death was lower in those vaccinated versus unvaccinated.
Conclusions: First and second SARS-CoV-2 vaccine doses appear effective in the short-term, but with diminishing effectiveness over time. The extremely low COVID-19 mortality, regardless of vaccination, indicates strong protection of previous infection against COVID-19 death. Lower non-COVID-19 mortality in the vaccinated population might suggest a healthy vaccinee bias.
Keywords: COVID-19; SARS-CoV-2; mortality; observational study; vaccine.
. 2024 Sep 19;11(10):ofae547.
doi: 10.1093/ofid/ofae547. eCollection 2024 Oct. Effectiveness of the First and Second Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine Dose: A Nationwide Cohort Study From Austria on Hybrid Versus Natural Immunity
Alena Chalupka 1 2 , Uwe Riedmann 1 , Lukas Richter 2 3 , Ali Chakeri 2 4 , Ziad El-Khatib 2 , Martin Sprenger 5 , Verena Theiler-Schwetz 1 , Christian Trummer 1 , Peter Willeit 6 7 8 , Harald Schennach 9 , Bernhard Benka 2 , Dirk Werber 2 , Tracy Beth Høeg 10 11 , John P A Ioannidis 12 , Stefan Pilz 1
Affiliations
- PMID: 39371370
- PMCID: PMC11450622
- DOI: 10.1093/ofid/ofae547
Background: We aimed to evaluate the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinations in previously SARS-CoV-2-infected adults in the general population of Austria during the Delta wave and with extended follow-up.
Methods: In a nationwide retrospective cohort study, we calculated age-, sex-, and nursing home residency-adjusted Cox proportional hazard ratios (HRs) of coronavirus disease 2019 (COVID-19) deaths, SARS-CoV-2 infections, and non-COVID-19 deaths from 1 October to 31 December 2021, and secondarily with extended follow-up to 30 June 2022. Relative vaccine effectiveness (rVE) is rVE = (1 - HR) × 100.
Results: Among 494 646 previously infected adults, 169 543 had received 2 vaccine doses, 133 567 had received 1 dose, and 190 275 were unvaccinated at baseline. We recorded 17 COVID-19 deaths (6 vaccinated, 11 unvaccinated) and 8209 SARS-CoV-2 infections. Absolute risk of COVID-19 deaths was 0.003%. rVE estimates for COVID-19 deaths and reinfections exceeded 75% until the end of 2021 but decreased substantially with extended follow-up. The risk of non-COVID-19 death was lower in those vaccinated versus unvaccinated.
Conclusions: First and second SARS-CoV-2 vaccine doses appear effective in the short-term, but with diminishing effectiveness over time. The extremely low COVID-19 mortality, regardless of vaccination, indicates strong protection of previous infection against COVID-19 death. Lower non-COVID-19 mortality in the vaccinated population might suggest a healthy vaccinee bias.
Keywords: COVID-19; SARS-CoV-2; mortality; observational study; vaccine.