Evaluating voluntary care seeking effects on COVID-19 outcomes and health system costs.

In an endemic COVID-19 setting with reduced enforcement measures, intervention success increasingly depends on voluntary compliance behaviors shaped by risk perceptions and population immunity. We used a previously developed behavior adaptation model, calibrated to Omicron wave data (February 1-May 31, 2022) in South Korea, to compare health outcomes (cumulative incidence, treated cases) and costs (vaccination, testing, treatment) under two scenarios: only mandatory compliance versus a combination of mandatory and voluntary compliance. The model included constant (mandatory) rates, independent of risk perceptions, and dynamic (voluntary) rates driven by changing perceptions of prevalence and severity. Sensitivity analyses identified key drivers of cumulative incidence and total costs. Introducing voluntary compliance reduced incidence by 14% while increasing total costs by 35% compared with a mandatory-only approach (37 million COVID-19 infected cases and $1.02 billion total cost over the four months in a 52 million Korean population). Information dissemination was one of the key drivers: under high coverage, emphasizing responsiveness to prevalence reduced incidence by 46% (vs. 11% under low coverage) but increased costs by 57% (vs. 29% under low coverage) due to greater care-seeking. Under high partial immunity, enhanced testing responsiveness reduced cases by 18% yet raised costs up to 40%, whereas improved vaccination responsiveness lowered incidence by 5% with only up to 10% cost increase. From the cost-effectiveness perspective, however, enhanced vaccination responsiveness outperformed testing alone (ICER $51, 95% Confidence Interval, CI 35-81, vs. $64, 95% CI 42-96, per case averted). Maximizing both testing and vaccination responsiveness provided the largest reduction in cases (-23%) at a 46% increase in total costs, leading to an ICER of $57, 95% CI 42-80, per case averted compared to the mandatory-only scenario. Voluntary testing plays a larger role in reducing disease burden than voluntary vaccination but incurs significantly higher costs. Strategies to improve cost-effectiveness could include lowering testing costs while encouraging voluntary vaccination. Given uncertainties around risk perceptions and voluntary behaviors, more detailed behavioral data and adaptive modeling can guide sustainable and cost-effective public health strategies.