COVID-19 Antiviral Delivers Better Benefits Than Expected

When the antiviral nirmatrelvir plus ritonavir (Paxlovid™) was granted U.S. Food and Drug Administration Authorization for treating COVID-19 in December 2021, little was known about whether the innovative antiviral would significantly benefit vaccinated individuals, as well as individuals infected with novel variants of the SARS-CoV-2 coronavirus that were not dominant during the pill's initial clinical trials.

The good news is Mass General Brigham researchers in Boston, MA, recently confirmed that Paxlovid is associated with a 44% reduction in hospitalization or related fatality in a highly vaccinated population of older adults.

This study's results, now published in the peer-reviewed Annals of Internal Medicine journal, suggest that Paxlovid can substantially benefit even vaccinated patients diagnosed with COVID-19 in the outpatient setting.

And can contribute to ongoing efforts to reduce COVID-19 hospitalizations during a projected winter surge of 2022-2023.

"When nirmatrelvir plus ritonavir was first becoming available for treating COVID-19, providers and patients asked important questions about who might benefit the most from this intervention, which can pose complications under certain circumstances," said corresponding author Scott Dryden-Peterson, MD, medical director of Mass General Brigham's COVID outpatient therapy, in a press release on December 12, 2022.

"The observed rate of hospitalization or death was low (1%) among outpatients diagnosed with COVID-19."

Furthermore, "we found that Paxlovid was still associated with a proportional reduction of risk for hospitalization of about 50% across patient groups with different baseline risk levels."

Dryden-Peterson and team suggest that the lower magnitude of risk reduction seen in this study compared to the clinical trial may be the result of different study contexts, as patients in this study overall had high levels of prior immunity and consequently lower risks of severe disease.

However, among the small minority of patients with fewer than three vaccine doses, there was an 81% reduction in hospitalization, a rate comparable to that found in the original trial.

Notably, no hospitalizations (69 total) in those treated with Paxlovid were attributed to a "rebound syndrome" that has been described in some patients after their symptoms appear to initially resolve after using the antiviral.

The U.S. National Institutes of Health funded this study. And these researchers did not disclose industry conflicts of interest. Pfizer Inc produces Paxlovid.

As of December 5, 2022, Paxlovid is the U.S. CDC preferred antiviral treatment for COVID-19 patients.