Estimates of SARS-CoV-2 Infections and Population Immunity After the COVID-19 Pandemic in Austria: Analysis of National Wastewater Data

Abstract Background Postpandemic surveillance data on coronavirus disease 2019 (COVID-19) infections may help inform future public health policies regarding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing, vaccinations, or other COVID-19 measures. We estimate the total SARS-CoV-2 infections in Austria after the end of the pandemic from wastewater data and utilize these estimates to calculate the average national levels of SARS-CoV-2 infection protection and COVID-19 death protection. Methods We estimated the total SARS-CoV-2 infections in Austria after the end of the pandemic (5 May 2023, per World Health Organization) up to May 2024 from wastewater data using a previously published model. These estimates were used in an agent-based model (ABM) to estimate average national levels of SARS-CoV-2 infection protection and COVID-19 death protection, based on waning immunity estimates of infections and vaccination in previous literature. Results We estimate approximately 3.2 million infections between 6 May 2023 and 23 May 2024, with a total of 17.8 million infections following 12 May 2020. The ABM estimates that the national average death protection was approximately 82% higher in May 2024 than before the pandemic. This represents a relative decrease of 8% since May 2023. It also shows that 95% of people in Austria were infected with SARS-CoV-2 at least once by May 2024. National infection protection remained relatively low after the onset of Omicron. Conclusions These findings should be considered for public health decisions on SARS-CoV-2 testing practices and vaccine booster administrations.