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Adjudication committee
- First opponent: Associate professor Christian Holm Hansen, London School of Hygiene and Tropical Medicine and Statens Serum Institiut, Denmark,
- Second opponent: Senior Researcher Mirjam Knoll, Center of Infectious Disease Control, The Netherlands
- Third member and chair of the evaluation committee: Professor Marit Inngjerdingen, University of Oslo
Chair of the Defence
Professor emeritus, Tore G. Abrahamsen, University of Oslo
Summary
This thesis belongs to the field of infectious disease epidemiology. It examines the epidemiology of the three dominant SARS-CoV-2 variants in Norway—Alpha, Delta, and Omicron— from February 2020 to January 2022. More specifically, the studies assessed the reinfection risk, disease severity, and vaccine effectiveness (VE) against infection with the different variants. The thesis is based on seven retrospective, registry-based cohort studies using data from the Norwegian Emergency Preparedness Register for COVID-19 (Beredt C19).
The results showed that the risk of reinfection was highest during the Omicron wave and increased with time since previous infection, indicating waning natural immunity. Vaccination reduced the risk of reinfection. People infected with the Alpha variant had higher hospitalisation risk compared to those infected earlier in the pandemic. The Delta variant had a similar hospitalisation risk as Alpha, while the Omicron variant had a lower hospitalisation risk than Delta. Vaccinated people had a lower risk of hospitalisation. VE against infection was high against the Alpha and Delta variants after full vaccination (2 doses) but lower after only one dose. VE against Omicron infection was reduced and declined faster over time. Booster doses increased protection from infection.
The results underlined the importance of vaccination and booster doses in maintaining protection, particularly against emerging variants. The findings were crucial in guiding public health interventions, including vaccination strategies, and preparedness plans for surge capacity in the hospital sector in Norway. The thesis also highlights the need for continuous monitoring of disease severity and VE as variants and vaccines evolve. The use of Beredt C19 registry during the pandemic enabled to timely research and provides valuable lessons for managing future health crises.
Additional information
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