Post-pandemic SARS-CoV-2 infection incidence: a Dutch prospective seroepidemiological cohort study

After the acute phase of the COVID-19 pandemic, surveillance was reduced and serological monitoring became crucial to monitor SARS-CoV-2 infections. We estimated infection incidence in the Netherlands during 2023–2024 using repeated serological sampling. We used data from randomly-selected Dutch citizens aged 2-92 years that participated in the nationwide seroepidemiological PIENTER-Corona cohort study. Blood samples were collected thirteen times since April 2020 including four times in the period April 2023–October 2024 and tested for IgG antibodies against Spike-S1 (S1) and Nucleoprotein (N). Infections were identified through anti-N and/or anti-S1 (if not vaccinated) seroconversion or ≥ 4-fold increase, and self-reported positive tests. We estimated the weighted infection incidence (≥1) in 2023–2024 (N = 4261) and total infection count by October 2024 (N = 4574) in the Dutch population, overall and stratified by age, sex, ethnicity, comorbidities and healthcare profession. Between April 2023 and October 2024, the weighted infection incidence was 59.1% [56.8–61.4]; 55.4% was infected once and 3.7% was infected twice or more. Higher infection rates were seen in 30-60 year-olds (ranging 63.3–68.5%), those without comorbidities (62.0%) and those not working in healthcare (62.9%). By October 2024, the median infection count since the start of the pandemic was two; 21.9% had experienced one infection, 50.0% had two and 24.3% had three or more infections. A significant proportion (∼60%) of the Dutch population was infected with SARS-CoV-2 at least once in this 1.5-year post-pandemic period, with incidence varying between sociodemographic groups. These results highlight the importance of serological data to monitor and establish infection incidence in the absence of large-scale testing policies. This information is vital for evaluating disease burden.

Key messages

• Approximately 60% of the Dutch population experienced at least one SARS-CoV-2 infection in a 1.5 year post-pandemic period between April 2023 and October 2024.

• When large-scale testing is unavailable, serological data are crucial for monitoring and establishing infection incidence, and provide essential information for evaluating disease burden.