Veterans Health Administration COVID-19 (VACO) Index for COVID-19 Mortality

The Veterans Health Administration COVID-19 (VACO) Index is a prognostic model developed to estimate a patient’s 30-day all-cause mortality risk after COVID-19 infection using information that is available before or at the time of diagnosis. Its main purpose is to identify people at higher short-term risk based on baseline health status, rather than on hospital-only data such as oxygen requirement or laboratory tests.

What the VACO Index uses

The VACO Index was derived from administrative and clinical data in the US Veterans Health Administration. The core model uses age, sex, Charlson Comorbidity Index (CCI), and a history of myocardial infarction (MI) or peripheral vascular disease (PVD); age was the strongest predictor in the original paper. In that derivation study, mortality ranged from about 0.3% in people younger than 50 years to about 44% in those aged 90 years or older.

This structure made the score practical early in the pandemic because it relied on routinely available pre-COVID information rather than inpatient physiology. That gave it potential value for outpatient triage, vaccination prioritization, and identifying which newly diagnosed patients might need closer attention.

How it was developed

The original VACO study included 13,323 patients with COVID-19 from VA data and validated the model in two prospective samples. The authors reported that the index had good discrimination for 30-day mortality, with area under the curve values of about 0.79 in development, 0.81 in early validation, and 0.84 in late validation.

A useful feature of the VACO Index is that it estimates absolute mortality probability, not just relative risk ranking. The original paper emphasized that even within the same age band, predicted mortality varied substantially depending on comorbidity burden and sex. For example, among people aged 60 to 64 years, estimated mortality varied from roughly 4% to 21% depending on these additional factors.

External validation and later performance

Later work tested the VACO Index in broader populations outside the original VA cohort, including Yale New Haven Hospital patients and Medicare populations. These analyses found that the model continued to show good discrimination across diverse groups, supporting its generalizability beyond the mostly older male veteran population from which it was derived.

A 2022 validation paper concluded that the VACO Index could estimate short-term mortality across a wide variety of patients and suggested it may help guide decisions such as booster prioritization and identifying COVID-positive outpatients who may deserve greater clinical attention or scarce treatments.

Strengths of the VACO Index

One of the main strengths of the VACO Index is its simplicity. It avoids the need for lab data or imaging and instead uses background clinical information that is usually already present in the medical record. That makes it easier to apply at the point of diagnosis, especially in non-hospital settings.

Another strength is that it focuses on baseline vulnerability, which is clinically useful when decisions must be made before a patient deteriorates. In this sense, the VACO Index differs from many inpatient scores that are designed only after hospitalization.

Limitations

The VACO Index was developed during earlier phases of the pandemic, before widespread vaccination, major treatment changes, and the emergence of later variants. For that reason, later studies noted that the model can overestimate mortality in some newer settings, especially among lower-risk or asymptomatic patients.

It also reflects the population in which it was created: the VA cohort was predominantly older and male, so calibration may differ in younger, healthier, or non-US populations. External studies have generally supported its usefulness, but they also show that local recalibration may be important when background mortality changes.

A further limitation is that VACO predicts mortality, not other outcomes such as hospitalization, long COVID, or need for ventilatory support. It should therefore be used as one part of a broader clinical assessment rather than as a stand-alone decision rule.

Clinical role

Today, the VACO Index is best understood as a baseline risk stratification tool. It can help estimate how much a patient’s pre-existing health status increases short-term mortality risk after COVID-19 infection, but its output should be interpreted in light of current epidemiology, vaccination status, treatments, and local population characteristics.

Bottom line

The VACO Index is a practical model for estimating 30-day mortality after COVID-19 infection using pre-COVID demographic and comorbidity data. Its main advantages are ease of use and good external validation, while its main limitations are changing pandemic-era calibration and the fact that it was derived in a veteran-heavy population. It remains a useful historical and clinical example of early outpatient-facing COVID-19 risk prediction.

References

1. King JT Jr, Yoon JS, Rentsch CT, et al. Development and validation of a 30-day mortality index based on pre-existing medical administrative data from 13,323 COVID-19 patients: the Veterans Health Administration COVID-19 (VACO) Index. PLoS One. 2020.
2. King JT Jr, Rentsch CT, Lei Y, et al. Accuracy of the Veterans Health Administration COVID-19 (VACO) Index for predicting short-term mortality among 1,307 Yale New Haven Hospital inpatients and 427,224 Medicare patients. J Epidemiol Community Health. 2022.
3. Matera-Witkiewicz A, Kęska A, Brzecka A, et al. Usefulness of the Veterans Health Administration COVID-19 (VACO) Index for predicting short-term mortality among patients of the COLOS study. Journal of Clinical Medicine. 2023.
4. Park M, Cook AR, Lim JT, Sun Y, Dickens BL. Prognostic utility of procalcitonin, presepsin, and the VACO Index in hospitalized COVID-19 patients. 2022. Includes a summary of the VACO variable structure.
5. Myers LC, et al. Performance of predictive models for 30-day hospitalization and mortality in COVID-19. 2022. Discusses VACO in comparison with other risk tools.