‘CV19 Hospitalizations’ Are an Increasingly Misleading Measure of Severe Disease

Since the beginning of the COVID-19 pandemic, researchers, policy makers, and journalists have viewed hospitalizations as an important indicator of the disease burden, often citing increases in that measure as a justification for government interventions aimed at curtailing virus transmission, such as business restrictions and mask requirements. Hospitalization numbers do have advantages over case tallies, which are highly dependent on who happens to be tested, and fatality reports, which are a lagging indicator, since deaths may be recorded weeks after diagnosis. But because hospitalization rates reflect patients who test positive for COVID-19, they do not tell us how many were admitted for treatment of the disease or how many experienced severe symptoms.

A newly published preprint study addresses those gaps in knowledge by applying measures of disease severity to about 48,000 V.A. hospital admissions of more than 38,000 COVID-positive patients between March 1, 2020, and June 30, 2021. The researchers, all but one of whom work for the V.A. Boston Healthcare System, found that the share of admissions involving moderate-to-severe COVID-19 cases fell from 64 percent before vaccines were widely available to 52 percent afterward.

In other words, incidental or mild cases accounted for a rising share of so-called COVID-19 hospitalizations—nearly half by the end of June. That means it is increasingly problematic to treat that number, which includes COVID-19 patients without life-threatening symptoms as well as COVID-positive patients admitted for other reasons, as an indicator of severe disease. Notably, the Centers for Disease Control and Prevention, which collects data on what are commonly called “COVID-19 hospitalizations,” uses a more ambiguous term: “COVID-19-associated hospitalizations.” But even that description is misleading, since the tally includes many hospital patients who were not admitted for treatment of COVID-19.

The main measure of disease severity in the V.A. study was an oxygen saturation level below 94 percent, which corresponds with “the most stringent cut-off” on a scale developed by the National Institutes of Health. The researchers also considered whether patients received the steroid dexamethasone, which reduces mortality in COVID-19 patients on supplemental oxygen or mechanical respiratory support. By both measures, the prevalence of moderate-to-severe cases declined with the advent of vaccines.

The researchers cite two explanations for that trend: Vaccination protects people against severe disease even if they are infected by the coronavirus, and “unvaccinated patients tend to be younger and healthier,” meaning they are less likely to experience life-threatening systems. Another factor could be the criteria that hospitals use for admitting COVID-19 patients, which are apt to be less demanding when the infected population becomes younger and healthier. But the upshot is that “COVID-19-associated hospitalizations,” which were always an imprecise measure of severe disease, should be viewed with even more caution now.

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