CNN  — 

Measures to protect patients hospitalized with Covid-19 from financial liability have been rolled back by most insurers in the United States, leaving the vast majority of patients with an average out-of-pocket bill of about $4,000 for each hospital stay, according to research published this week in the journal JAMA Network Open.

Between March 2020 and January 2021, less than 9% of patients with private health care insurance had any cost-sharing associated with Covid-19 hospitalization. By March 2021, more than 84% of patients with private insurance had some financial responsibility for a Covid-19 hospitalization.

A separate analysis by the Kaiser Family Foundation found that cost-sharing waivers have now expired for more than 94% of the largest health insurance plans. The vast majority had rolled them back by August 2021, when Covid-19 vaccines were widely available to the general public.

Patients insured under the Medicare Advantage program saw a similar jump in cost-sharing responsibilities, from less than 3% in the first year of the pandemic up to 66% in March 2021.

From March 2020 through March 2021 – spanning periods when cost-sharing waivers were both widespread and rolled back – the average Covid-19 hospitalization cost privately insured patients an average of $3,998 out-of-pocket. Average costs were highest in the Western region of the US and lowest in the Northeast.

For this study, researchers from the University of Michigan and Boston University analyzed medical claims for nearly 16,000 people hospitalized with Covid-19 as their primary diagnosis.

The researchers suggest that the “widespread abandonment of insurer cost-sharing waivers is arguably premature.”

“While the potential size of these bills may convince a few patients to become vaccinated, it could also prompt patients to delay seeking care irrespective of vaccination status, as both the vaccinated and unvaccinated are both now subject to cost sharing,” they wrote.

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Nearly 69,000 people are currently hospitalized with Covid-19 in the United States, with more than 9,500 new admissions each day, according to federal data. Although hospitalizations have dropped to less than half of what they were at the peak of the Omicron wave in January, they’re still higher than they’ve been for most of the pandemic.

In December, the risk of hospitalization was 44 times higher for unvaccinated adults than it was for adults who were fully vaccinated and boosted, according to data from the US Centers for Disease Control and Prevention.