A combination of two monoclonal antibody treatments keeps high-risk COVID-19 patients out of the hospital when infected with mild to moderate disease, according to an observational study published in The Lancet's EClinicalMedicine journal.

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Monoclonal antibodies are laboratory-produced molecules engineered to serve as substitute antibodies that can restore, enhance or mimic the immune system's attack on pathogens. The combination of the monoclonal antibody treatments casirivimab and imdevimab has been given emergency use authorisation (EUA) by the US Food and Drug Administration (FDA).

The research enrolled nearly 1,400 patients at Mayo Clinic in the US, of whom 696 received the drug combo between December 2020 and early April while an equal matched cohort did not receive it. The disease status of the patients was evaluated at 14, 21 and 28 days after treatment. At each point, the numbers for hospitalisation were significantly lower in the treated group.

At day 14, 1.3 per cent of the treated group were in the hospital, compared to 3.3 per cent of those who had not been treated, the researchers said. At day 21, only 1.3 per cent treated were hospitalised, compared to 4.2 per cent of those who had not been treated, they said. The study found that at the end of 28 days, 1.6 per cent of those treated were hospitalised versus 4.8 per cent of those who had not been treated.

This translated to 60-70 per cent relative reduction in hospitalisation among treated patients, according to the researchers. Of those who were subsequently hospitalised, the rates of ICU admission and mortality were low, they found.

"Once again, this real-world study suggests that when patients who are at high risk due to a range of comorbidities contract a mild or moderate case of COVID-19, this combination of monoclonal injections gives them a chance of a nonhospitalised recovery. In other words, they recover safely at home," said Raymond Razonable, an infectious diseases specialist at Mayo Clinic, and senior author of the study.

A previous study by Mayo Clinic researchers suggested the use of bamlanivimab reduced hospitalisations in high-risk patients by 40 60 per cent. That study involved 2,335 treated patients from Mayo Clinic between November of 2020 and February.

Comparing their outcomes with 2,335 untreated patients, the ICU admission and mortality rates also were significantly lower with monoclonal antibody treatment. The researchers noted that the FDA in April revoked the EUA for bamlanivimab alone and now endorses use of combination monoclonal antibodies. "Our conclusion overall at this point is that monoclonal antibodies are an important option in treatment to reduce the impact of COVID-19 in high-risk patients," Razonable added.