Estimates of SARS-CoV-2 infections and population immunity after the COVID-19 pandemic in Austria: Analysis of national wastewater data

ABSTRACT Background Post-pandemic surveillance data on COVID-19 infections may help inform future public health policies regarding 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 (May 5, 2023, per WHO) up to May 2024 from wastewater data. Those estimates are used in an agent-based model (ABM) to estimate average national levels of SARS-CoV-2 infection protection (IP) and COVID-19 death protection (DP). Methods We use a previously published model estimating total infections in Austria from wastewater data and extrapolate the approach up to May 2024. Utilizing those estimates in an ABM, we estimate daily national average IP and DP. These estimates are based on waning immunity estimates of previous literature and incorporate documented vaccinations. Findings We estimate approximately 3·2 million infections between May 6, 2023, and May 23, 2024, with a total of 17·8 million infections following May 12, 2020. The ABM estimates that 95% of people in Austria were infected with SARS-CoV-2 at least once. It also shows very high levels of national average DP a year after the end of the pandemic. National IP remained relatively low after the onset of Omicron. Interpretation The estimated high number of SARS-CoV-2 infections since the end of the COVID-19 pandemic in Austria has kept the national average DP very high. These findings should be considered for public health decisions on SARS-CoV-2 testing practices and vaccine booster administrations. Funding Austrian Science Fund (FWF) KLI 1188.