Doctoral defence: Tatjana Meister "Assessing COVID-19 risk and sequelae: the role of vaccination in modifying infection, severity, and long-term outcomes”

On the 12th of December 2025 Tatjana Meister will defend her thesis "Assessing COVID-19 risk and sequelae: the role of vaccination in modifying infection, severity, and long-term outcomes”.

Supervisors:
Associate Professor of Family Medicine Kadri Suija, University of Tartu
Professor of Family Medicine Ruth Kalda, University of Tartu
Professor of Epidemiology Anneli Uusküla, University of Tartu

Opponent:
Associate Professor Lena Margareta Thorn, University of Helsinki (Finland)

Summary:
The COVID-19 pandemic shook the entire world and placed unprecedented pressure on healthcare systems. The multifaceted clinical picture of the disease, high mortality, and involvement of multiple organ systems placed a significant burden on healthcare, forcing the implementation of extensive measures to limit the spread of the virus. The long-term health effects of COVID-19 are still being studied, but preliminary data suggest links to a decline in quality of life and persistent physical complaints, as well as an increased incidence of cardiovascular, metabolic, and neurological diseases.

Based on three Estonian population-based cohort studies, the research used national electronic health databases and aimed to identify factors influencing the risk of COVID-19 and the long-term consequences of the disease. The research showed that the risk of infection was higher in women and people of working age, while a higher level of education reduced the likelihood of SARS-CoV-2 breakthrough infection. The severity of the disease increased with age and the number of comorbidities. COVID-19 vaccination significantly reduced the impact of these factors, but the risk of hospitalization remained high for certain diseases, such as chronic kidney disease, diabetes, and chronic lung disease.

People with dementia were less likely to be hospitalized in intensive care units, even though their risk of death from COVID-19 was high. The vaccine's protective effect against infection was short-lived, although protection against severe COVID-19 lasted for at least six months, and a booster dose provided additional protection. In addition, COVID-19 vaccination reduced the risk of acute cardiovascular events and death after infection, although this effect was limited in time and varied by age and sex.

The study results support risk-based prevention measures, enhanced surveillance after illness regardless of vaccination status, and viewing vaccination more broadly than just a means of modifying disease severity. Prevention strategies must take into account changing risks and vulnerable groups whose risk may not be completely eliminated by vaccination and who must be guaranteed equal access to treatment.