The findings are a huge disappointment for Adagio, which billed ADG20 as a weapon that could neutralize a wide range of variants and help with future outbreaks. The company is aiming to develop a single injection that can treat Covid-19 and prevent new infections for as long as a year.

Adagio said it’s “evaluating next steps” for the drug. For now, the company will stop recruiting patients into its Phase 2/3 clinical trial in South Africa, where omicron was first identified. Still, Adagio emphasized that the experimental treatment appears to work against other variants of concern, including delta.

With delta still prevalent and the potential for different mutations in the future, “a multitude of therapies and approaches are needed,” Adagio CEO Tillman Gerngross said in the company’s statement.

Adagio isn’t alone in encountering difficulties with omicron. Early lab research suggests that the variant can escape most antibody treatments. One notable exception is a drug developed by Vir Biotechnology and GlaxoSmithKline, which still functioned with “reduced efficacy” in a recent study.

The bad news for antibody treatments raises the possibility that patients will need to be tested for their COVID-19 strains and treated with variant-specific medicines, another group of researchers suggested. That could be particularly daunting in the U.S., where testing to identify variants lags other countries.

Adagio had one of the larger financing rounds for a privately held biotech earlier this year, raising $336 million. The company then went public, and its stock was trading close to $40 a week ago. The shares closed at $7.26 Tuesday and continued to drop Wednesday, down another 20% to below $6 in early trading.