» Merck abandons 2 vaccines in clinical trials.

Merck announced Monday that it was abandoning a pair of COVID-19 vaccines in clinical trials.

The news came as a disappointment at a time when the United States and other countries are struggling to accelerate their sluggish vaccination campaigns and new coronavirus variants threaten to bring surges over the next few months.

The two projects are the second and third vaccines to be abandoned in clinical trials. The University of Queensland in Australia abandoned its own effort in December. Sanofi and other vaccine-makers have paused some projects after getting disappointing initial results but are now regrouping to move forward.

Researchers began a Phase 1 trial in August. In a second effort, Merck partnered with IAVI, a nonprofit scientific organization that develops vaccines and treatments, on another vaccine.

Merck will instead focus its COVID-19 efforts on an experimental antiviral drug known as molnupiravir. Originally designed for influenza, it has shown promising effects in studies on animals and in early clinical trials. The trial is set to finish by May, although preliminary results could come out as early as March.

IAVI said it would continue searching for COVID-19 vaccines.