The antiviral medications remdesivir and a related compound, obeldesivir, continue to show effectiveness against a wide range of Omicron subvariants of SARS-CoV-2, according to recent laboratory studies. This finding, published in January 2026, offers reassurance as the virus continues to evolve and new strains emerge. Understanding the antiviral activity of remdesivir and obeldesivir against these variants is crucial for informing treatment strategies and public health responses.
Researchers evaluated the drugs’ ability to inhibit the virus in laboratory settings using both clinical isolates – samples taken directly from patients – and a replicon system, which mimics viral replication. The study, conducted by scientists at Gilead Sciences, Inc., focused on variants circulating from September 2023 through March 2024, including JN.1.7, KP.2, KP.3.1.1, LP.8.1, NB.1.8.1, XEC, and XFG. These findings are particularly relevant as these Omicron subvariants gained prominence during the winter of 2023-2024 and continued to circulate into 2025.
Evaluating Antiviral Effectiveness in the Lab
The research team used a nucleoprotein enzyme-linked immunosorbent assay (ELISA) to measure the concentration of remdesivir and obeldesivir needed to reduce viral load by 50% (EC50) in cells infected with the various Omicron subvariants. The cells used in the study, A549-hACE2-TMPRSS2, are commonly used in COVID-19 research because they express the human ACE2 receptor, which the virus uses to enter cells. For variants where clinical isolates weren’t readily available – LP.8.1, NB.1.8.1, and XFG – the researchers employed a replicon system, a method that allows them to study the virus’s replication process without needing a live virus sample.
The replicon system utilizes fragments of the original SARS-CoV-2 strain (SARS-CoV-2/human/CHN/SH01/2020, GenBank MT121215) and introduces specific mutations found in the newer variants. This allows scientists to assess how these mutations affect the drugs’ ability to block viral replication. The replicon was introduced into Huh7-1CN cells, which express the SARS-CoV-2 nucleoprotein, and then treated with varying concentrations of remdesivir and obeldesivir.
Consistent Activity Across Variants
The study found that both remdesivir and obeldesivir maintained their antiviral activity against all tested Omicron subvariants. Crucially, the researchers observed no significant changes in the drugs’ effectiveness compared to the original WA1 reference strain. The variability in EC50 values for remdesivir ranged from 44.2 nM to 196.8 nM, with a signify of 112.1 nM for the wild-type clinical isolate. For obeldesivir, the EC50 values ranged from 1.43 μM to 4.17 μM, with a mean of 2.29 μM. The researchers established thresholds for variability, and variants falling within these thresholds were considered to have a similar response to the drugs as the original strain.
The researchers also analyzed 29 polymorphisms identified in the Nsp12 protein of the Omicron variants. Nsp12 is a key enzyme involved in viral replication, and remdesivir and obeldesivir function by inhibiting its activity. Phenotypic analysis confirmed that these polymorphisms did not impact the antiviral activity of either drug, further supporting the continued efficacy of these treatments.
Implications for Treatment and Future Research
These findings support the continued utilize of remdesivir in treating COVID-19, even as the virus evolves. Remdesivir (VEKLURY®) is currently an approved antiviral treatment for the disease. The research also provides encouraging data for the development of obeldesivir as a potential new therapeutic option. The consistent activity of both drugs across a range of Omicron subvariants suggests that they remain valuable tools in the fight against COVID-19. Further research will be needed to monitor the virus’s continued evolution and assess the long-term effectiveness of these treatments.
The study highlights the importance of ongoing surveillance of SARS-CoV-2 variants and continuous evaluation of antiviral drugs. As new variants emerge, it’s essential to understand how they respond to existing treatments to ensure that healthcare providers have the information they need to produce informed decisions about patient care. The data presented here, published in Open Forum Infectious Diseases, provides a valuable contribution to this ongoing effort.
Looking ahead, Gilead Sciences continues to monitor the emergence of new SARS-CoV-2 variants and assess the antiviral activity of remdesivir and obeldesivir. The company is committed to providing updates on the drugs’ effectiveness as new data become available. Readers interested in learning more about COVID-19 treatments can consult with their healthcare provider or visit the Centers for Disease Control and Prevention website for the latest information.
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