In the randomized controlled trial, in both the group who received bamlanivimab and the group who received placebo, higher antigen and viral RNA levels were associated with a lower proportion of patients achieving recovery.
Other studies have shown that the use of monoclonal antibodies reduces hospitalization risk in outpatients with early COVID-19, and appears to promote viral load decline in the nasopharynx, wrote Jens D. Lundgren, MD, of the University of Copenhagen and colleagues in their article published in the Annals of Internal Medicine. What had been missing prior to this new research was final results from hospitalized patients, the authors said.
In the new study, the researchers randomized 314 adults hospitalized with COVID-19 but without end-organ failure to receive 7,000 mg bamlanivimab (163 patients) or a placebo (151 patients). All patients received study-supplied remdesivir unless contraindicated. The researchers compared the efficacy of bamlanivimab versus placebo, but considered remdesivir the standard of care in this study.
At baseline, 50% of patients overall had antispike endogenous neutralizing antibodies (nAbs), and 50% had SARS-CoV-2 nucleocapsid plasma antigen levels of at least 1,000 ng/L.
The median time to sustained recovery, 19 days, was not significantly different between the bamlanivimab and placebo groups (subhazard ratio, 0.99).
“As hypothesized, among those who were negative for nAb, the difference between bamlanivimab and placebo was more evident if levels of plasma antigen or nasal-swab viral RNA were above the median entry levels,” with subhazard ratios of 1.48 and 1.89, respectively, the researchers explained.
However, the hazard ratio for death for bamlanivimab vs. placebo was 0.45 for patients negative for nAb vs. 3.53 for those positive for nAb. These differences with respect to nAb status were similar across all 90 elements of a composite safety outcome, the researchers said.
Potential benefits remain unclear
The use of neutralizing monoclonal antibodies has been extensively documented as an effective treatment for COVID-19 among ambulatory patients, corresponding author Dr. Lundgren said in an interview.
“Conversely, among admitted patients with COVID-19 pneumonia, the benefit has been questionable,” he said.
The researchers examined a hypothesis that the null finding in hospitalized patients may stem from differences in underlying mechanisms, “either from uncontrolled viral replication – which would be predicted to occur in particular among those not yet been able to mount an endogenous immune response – or from hyperinflammation among those that have mounted such a response,” Dr. Lundgren said.
The study findings supported the stated hypothesis, said Dr. Lundgren. “However, it was surprising that not only was the neutralizing antibody without any benefit among those that had mounted an endogenous immune response, but it actually may have been harmful,” he said.
Bamlanivimab was effective against the viral strain that circulated at the time of enrollment in the study, but subsequent viral strains have appeared to be unaffected by the neutralizing activity of the antibody, said Dr. Lundgren.
From a practical standpoint, “the findings would suggest that use of neutralizing monoclonal antibodies for patients admitted to a hospital with COVID pneumonia should be restricted to those that have not yet mounted an endogenous immune response, as determined by lack of detectable neutralizing antibodies at the time of admission,” Dr. Lundgren said.
Looking ahead, studies are currently underway to examine how the findings translate to vaccinated patients, he added. Other questions to be addressed include whether the benefits and harms apply to some or all neutralizing antibody products, he said.
In addition, “our research consortium is currently doing field testing of several point-of-care test candidates to examine their reliability and functionality,” for how quickly they might identify an endogenous neutralizing antibody response in an admitted COVID pneumonia patient,” Dr. Lundgren noted.