Two studies have found that the virus that causes COVID-19 is becoming resistant to two drugs used to treat patients with infections.

In the first study, a combined team from Cornell University and the National Institutes of Health studied the treatment outcomes for patients with compromised immune systems who were given the drug remdesivir. They have published their results in the journal Nature Communications.

In the second study, a team of researchers from the University of Pittsburgh, Brigham and Women's Hospital, Stanford University and Harvard University studied the outcomes for COVID-19 patients given antiviral drugs over the years 2021 to 2023. They published their results in the journal JAMA Network Open.

Zhuo Zhou and Peng Hong, with the Chinese Academy of Medical Sciences & Peking Union Medical College and VA New York Harbor Healthcare System, respectively, have published a Commentary piece in the same JAMA Network Open issue outlining the work by the second team.

In the years since the height of the COVID-19 pandemic, medical researchers have continued to study SARS-CoV-2, along with new vaccine options. They have also been working on developing new therapies for people who are infected by the virus but have not been immunized or who have compromised immune systems.

As part of that effort, two such therapies, named remdesivir and nirmatrelvir, have become the go-to drugs for patients with immune systems that are not capable of fighting off the virus. But because they are antivirals, they run the risk of obsolescence as the virus mutates.

In the first study, the researchers sequenced the DNA of the virus infecting 15 COVID patients and found that the virus had developed a reduced sensitivity to both remdesivir and nirmatrelvir. They also found that the mutated viruses could infect others in the vicinity. One positive note: The researchers found that giving both antivirals to patients cleared the virus.

In the second study, the research team studied the treatment of 156 COVID-19 patients over two years—as part of that effort, the researchers divided the patients into two groups: those who had received the antiviral drugs and those who had not. Viruses with antiviral-resistant mutations were more likely to be found in patients who had received antiviral drugs. The effect was more evident in the immunocompromised and those who had received nirmatrelvir.