While much of the population has gained some immunity to COVID-19, the risk of severe disease remains a concern for individuals with comorbidities or compromised immune systems. Recent research is providing hope through novel prophylactic and therapeutic strategies.
Paxlovid's Ongoing Role
Initial findings from the phase II/III EPIC-HR trial indicated that nirmatrelvir/ritonavir (Paxlovid) was highly effective, demonstrating nearly 89% efficacy in preventing COVID-19-related hospitalization and all-cause mortality among unvaccinated, high-risk patients. However, the applicability of these results in settings with widespread population immunity has been questioned.
John McLaughlin, PhD, of Pfizer, addressed this issue at IDWeek, noting that the EPIC-SR trial, which included standard-risk individuals and vaccinated people with risk factors, did not show a significant reduction in symptom duration with Paxlovid. There was, however, a non-significant trend toward fewer hospitalizations and deaths.
To clarify Paxlovid's utility, researchers conducted a pooled analysis of data from both trials. The results indicated that nirmatrelvir-ritonavir effectively reduced COVID-related outcomes in high-risk, vaccinated, or previously infected patients. Hospitalization or death occurred in 0.5% of the nirmatrelvir-ritonavir group versus 1.9% in the placebo group, representing a 73.7% relative risk reduction (95% CI 21.4-91.3). A 65% relative reduction in COVID-related medical visits (95% CI 24.4-83.8) and a 46.6% relative reduction in severe COVID symptoms (95% CI 22.1-63.4) were also observed.
The number needed to treat (NNT) to prevent one hospitalization or death was 71, while the NNT to prevent a COVID-related medical visit was 24, and the NNT to reduce severe COVID symptoms was 16. McLaughlin concluded that these findings support the continued use of Paxlovid in high-risk patients, even with existing SARS-CoV-2 immunity.
Addressing Unmet Needs in COVID Prevention
Dinesh De Alwis, PhD, of Generate:Biomedicines, emphasized the need for new COVID-19 prevention and treatment options, especially for immunosuppressed individuals and those undergoing cancer treatment. He highlighted that COVID-19 is a major cause of non-relapse deaths in patients undergoing B-cell-depleting CAR-T therapy, with infections accounting for over 50% of these deaths. Vaccine responses are often suboptimal in these patients, and chronic COVID-19 infections may not respond to monotherapy antiviral treatments.
Generate:Biomedicines is developing GB-0669, a novel monoclonal antibody effective against diverse sarbecoviruses, including multiple SARS-CoV-2 variants. GB-0669 targets the S2 stem helix (S2-SH) of the virus, a region less prone to immune escape compared to the receptor-binding domain (RBD) targeted by other antibodies. A phase I study showed that GB-0669 was well-tolerated, with a half-life of 55 days. The optimal therapeutic dose was determined to be 1,200 mg IV, providing an approximate 10-fold increase in neutralizing titers against SARS-CoV-2 in healthy participants. De Alwis suggested that a single dose of GB-0669 could protect against COVID-19 hospitalization for 60 days in patients with low baseline titer levels, supporting its advancement to phase II trials, particularly in immunocompromised populations.
Investigational Antiviral: Obeldesivir
Currently, available antivirals for COVID-19 treatment include nirmatrelvir-ritonavir, remdesivir, and molnupiravir. Obeldesivir, an investigational antiviral, is an oral prodrug of GS-441524, targeting the RNA-dependent viral RNA polymerase. The phase III BIRCH trial evaluated its efficacy and safety in individuals with risk factors for severe disease.
Lauren Rodriguez, PhD, of Gilead Sciences, reported that the BIRCH trial was halted early due to a lower-than-expected event rate for the primary outcome of COVID-related hospitalization or all-cause death (zero events in the obeldesivir group [n=211] versus one in the placebo group [n=207]). However, secondary endpoints indicated potential efficacy. Obeldesivir resulted in a greater reduction in SARS-CoV-2 viral load at day 5 compared to placebo (-0.58 log10 copies/mL, P <0.0001) and led to significant reductions in infectious titers on day 3 (-0.54 log10 PFU/mL, P =0.0003) and day 5 (-0.17 log10 PFU/mL, P =0.0014). At day 3, 80% of participants in the obeldesivir group and 49% in the placebo group were negative for infectious virus (P =0.0049), and at day 5, 100% and 81%, respectively, were negative (P =0.0001). The phase III OAKTREE study, evaluating obeldesivir as a COVID-19 treatment for people without risk factors for severe disease, is ongoing.
