The drugs behind the new pills to treat Covid-19 remain very effective against the Omicron variant of the virus in lab tests, according to a new study.
However, lab tests also showed that the available antibody therapies -- typically given intravenously in hospitals -- are substantially less effective against Omicron than against earlier variants of the virus.
Some antibodies have entirely lost their ability to neutralise Omicron at realistic dosage, found researchers from the University of Wisconsin-Madison.
The findings corroborate other studies that show most available antibody treatments are less effective against Omicron.
Drug makers could design, test and produce new antibody drugs targeted at the omicron variant to overcome the limitations of current therapies, but this process would take months.
"The bottom line is we have countermeasures to treat Omicron. That's good news," said Yoshihiro Kawaoka, the lead of the study and virologist at the UW School of Veterinary Medicine and the University of Tokyo.
"However, this is all in laboratory studies. Whether this translates into humans, we don't know yet,"Kawaoka said.
The findings were published in the New England Journal of Medicine.
The clinically available pills and antibodies were designed and tested before researchers identified the Omicron variant, which differs significantly from earlier versions of the virus.
In lab experiments using non-human primate cells, Kawaoka's team tested a suite of antibody and antiviral therapies against the original strain of the Covid-19 virus and its prominent variants, including the Alpha, Delta and Omicron strains.
Merck's pill molnupiravir and the intravenous drug remdesivir were just as effective against the Omicron variant as they were against earlier viral strains.
The team also tested a related drug by Pfizer that is given intravenously. The two drugs disrupt the same part of the viral machinery. The researchers found that the intravenous form of the drug retained its effectiveness against Omicron, and this version is currently in clinical trials.
All four antibody treatments the researchers tested were less effective against Omicron than against earlier strains of the virus.
Two treatments, sotrovimab by GlaxoSmithKline and Evusheld by AstraZeneca, retained some ability to neutralise the virus.
However, they required anywhere from 3 to 100 times more of the drugs to neutralise Omicron compared to earlier versions.
Two antibody treatments by Lilly and Regeneron were unable to neutralise omicron at common dosages.