Treating Omicron: Antivirals work, some antibody treatments do not
Although most antibodies were effective against the earlier variants, all monoclonal antibodies tested in the study showed a reduced ability to neutralize Omicron.
For instance, the Regeneron monoclonal antibody
casirivimab effectively neutralized Gamma and Beta, but to neutralize Omicron, 18–75 times higher concentrations of the antibody were necessary.
The GlaxoSmithKline antibody
sotrovimab was superior to other antibodies at neutralizing Omicron, with lower concentrations needed to inhibit it. Still, the concentrations of the drug that were able to neutralize the Omicron variant were three times higher than those for the
Delta or Beta variants.
Similar to monoclonal antibody treatments, the currently authorized COVID-19 vaccines were also designed to elicit an immune response against the wild-type SARS-CoV-2 spike protein.
Consistent with the results of the present study, other studies
have shown a
decline in the levels of neutralizing antibodies against Omicron in individuals who have received two doses of
mRNA vaccine.
These antibodies are important to prevent SARS-CoV-2 infection and at least partially explain the
higher number of breakthrough infections with the Omicron variant.
Antibody cocktails
Of the three, the AstraZeneca antibody combination Evusheld was most effective at inhibiting the ability of Omicron to infect cultured cells. Yet, the concentrations of the antibody combination that could neutralize the Omicron variant were as many as 24–142 times higher than those for the previous variants.
The other two antibody combinations failed to neutralize Omicron.
Incidentally, the reduced effectiveness of these two antibody combinations — produced by Eli Lilly and Regeneron Pharmaceuticals — has led the
FDA to discontinue the use of these drugs for COVID-19 caused by Omicron.
Antiviral drugs
These antivirals included remdesivir and
molnupiravir, both of which inhibit the key enzyme required for making copies of the SARS-CoV-2 genome. The researchers also tested an
IV version of a Pfizer candidate drug, which inhibits a SARS-CoV-2 enzyme required for the cleavage of viral proteins during replication.
The study authors tested these drugs, because Omicron has a single mutation in each of the two enzymes that these antivirals target.
They found that all three drugs were as effective against Omicron as they were against the earlier variants. The researchers caution, however, that these results from laboratory experiments need verifying in clinical studies.
“These data are consistent with results from several other studies. The laboratory studies show that the activity of several anti-SARS-CoV-2 monoclonal antibodies (casirivimab/imdevimab, bamlanivimab/etesevimab) is markedly reduced against Omicron. By contrast, in these lab studies, sotrovimab, another authorized anti-SARS-CoV-2 monoclonal antibody, continues to be active against Omicron.”
A study finds antibody treatments are less effective against Omicron than against earlier variants. By contrast, antiviral drugs maintained their effectiveness.
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They have fewer tools than they used to.