The drugs, called monoclonal antibodies, are laboratory-made proteins designed to mimic the immune system's ability to fight off viruses. Essentially, they are modeled after human antibodies against viruses.
Eleven days after one infusion of the monoclonal antibodies bamlanivimab and etesevimab, non-hospitalized patients infected with the coronavirus saw their viral loads -- or the amount of virus in their blood -- drop by 20%, the data showed.
However, experts say it remains unclear how the combination therapy impacts patient symptoms, and it is not known whether the approach can help those with more severe disease.
"It seems the combo has some impact on the viral load, but the meaning of that is unclear, especially given the inconsistent harmony between viral load reduction and symptom effect," infectious disease specialist Dr. Donald N. Forthal told UPI.
"What we would really like to see is more impact on symptoms," said Forthal, a professor of medicine and molecular biology at the University of California-Irvine's Center for Virus Research, who was not involved in the JAMA study.
Bamlanivimab and etesevimab are based on antibodies from two patients who recovered from COVID-19 -- one in North America and the other in China -- according to the JAMA researchers.
Lilly, which manufactures bamlanivimab, ended a trial in patients hospitalized with the virus early, in October, when it was found to provide no benefit.
"Monoclonal antibodies ... have typically been used to prevent, rather than treat, infections -- the best example [being] respiratory syncytial virus, or RSV, in premature babies," pediatric infectious disease specialist Dr. Josh Wolf told UPI.
"However, in this study, starting monoclonal antibodies targeted against the virus in adults with early, mild COVID-19 seemed to prevent worsening of their illness," said Wolf, who practices at St. Jude Children's Research Hospital in Memphis and was not part of the JAMA study.
For this study, 421 non-hospitalized patients with mild to moderate COVID-19 received either bamlanivimab alone, at one of three dosing levels, or in combination with etesevimab, the researchers said.
In addition, 156 received placebo, or a substance with no therapeutic effect, they said.
All treatments were administered in a single infusion, and patients were evaluated seven, 11, 15 and 22 days after receiving them.
Patients who received 700 milligrams, 2,800 mg. or 7,000 mg. of bamlanivimab alone did not see reductions in viral load at day 11, the researchers said.
However, those given an infusion containing 2,800 mg. of both bamlanivimab and etesevimab saw their COVID-19 viral loads drop by 20%, the data showed.
Still, there was no difference between the treatments given in the study in terms of symptoms, with patients in all groups reporting symptoms lasting four to five days, the researchers said.
In addition, up to 2% of patients who received antibody treatment required hospital or emergency room care for their COVID-19 infection, compared to 6% of those given a placebo, the data showed.
"Most people won't be able to tell if the drug helps them ... because most will recover on their own," Wolf said.
"There is some suggestion that people who don't need to go to hospital did feel better more quickly if they got the antibodies, but the difference was pretty small, and definitely could be due to chance," he said.