Merck announced the decision following a review of the findings of a phase I clinical study on its COVID-19 vaccine candidates, V590 and V591. While the vaccines were generally well-tolerated, immune responses were lower than what researchers saw following infection or immunization with another vaccine, the company noted.

As a result of the discontinuation, Merck will record a charge in the fourth quarter of 2020 that will affect the company's results under generally accepted accounting principles (GAAP) results but not its non-GAAP results. Merck and collaborators still plan to submit its V590 and V591 phase I study results for publication in scientific journals.

Despite the change, the company plans to continue to advance clinical programs for its investigational medicines, MK-7110 and MK-4482, the later of which, known as molnupiravir, is being developed in conjunction with Ridgeback Bio. Merck also intends to continue evaluating measles virus vector and vesicular stomatitis virus vector-based platforms.