Evaluating SARS-CoV-2 Vaccine Breakthrough Surveillance in Washington

Abstract

Abstract Context: Severe acute respiratory coronavirus 2 (SARS-CoV-2) vaccine breakthrough surveillance is a novel surveillance program implemented in Washington. The surveillance system monitors cases of COVID-19 among those fully immunized with COVID vaccine. As of June 2021, the Washington State Department of Health has been preparing to transition SARS-CoV-2 vaccine breakthrough case identification methods from relying only on passive reporting of potential cases to inclusion of active case ascertainment facilitated by linkage of the Washington Disease Reporting Database (WDRS) and the Washington Immunization Information System (WAIIS). Process evaluation is needed to inform surveillance program protocols and optimize use of resources.Objectives: Evaluate a proposed new surveillance method for SARS-CoV-2 vaccine breakthrough. Assess completeness of reporting under passive case reporting and compare active case ascertainment through data linkage. Evaluation Methods: This evaluation assessed attributes defined in Centers for Disease Control and Prevention guidelines for evaluating public health surveillance systems. Outcome measures of interest are both qualitative and quantitative. Primary measures of interest were sensitivity and positive predictive value. Secondary measures of interest were system flexibility, simplicity, data quality, acceptability, representativeness, and timeliness. Assessment was informed through data collection, direct observation, and surveillance system participant feedback. Analysis: Completeness of case identification was evaluated for both passive surveillance and active case ascertainment methodologies. The number of passively reported breakthrough cases in the first three months of surveillance was compared to the number of cases identified by linking positive COVID-19 cases to COVID-19 immunization records in the same time period. The passively detected cases that were not identified by data linkage were further examined to characterize the limitations of database linkage as an active case ascertainment methodology. Results: Passive surveillance is reasonably sensitive, detecting a net 62.3% of the number of vaccine breakthrough cases that were identified through data linkage in the time period of interest. Active case ascertainment has much higher sensitivity, estimated at 90.8% of total cases identified by combined methods. Addition of active case ascertainment is estimated to increase overall case identification by 52%. Conclusions: The system is flexible, acceptable to reporting organizations, and provides timely output. System simplicity is marginal but will be improved with the integration of active case ascertainment. Representativeness may be impacted by reliance on active case ascertainment only; cases whose immunization records are stored outside of WA IIS are only detected in passive surveillance. This limitation may be addressed by maintaining a passive reporting component in the surveillance system and by improving data sharing and collaboration between public health partners. The surveillance program is effective in meeting its objectives but increases in breakthrough incidence pose a threat to system stability. Swift adoption of active case ascertainment is recommended.