Merck announced that it is going to stop developing its two COVID-19 vaccine candidates, dubbed V590 and V591, after poor responses in Phase I trials. They are shifting their attention to advancing two therapeutic drugs for COVID-19, MK-4482 and MK-7110.
Merck came late to the vaccine race when it acquired Austria-based Themis in May 2020. The same month, it partnered with Florida-based Ridgeback Therapeutics to develop MK-4882, which is an orally-available antiviral candidate. And in November, it acquired Maryland-based OncoImmune and its COVID-19 candidate CD24Fc (MK-7110) for $425 million in upfront cash.
In the Phase I trials, V590 and V591 were generally well tolerated, but the company reports that immune responses were inferior to what was observed in people who recovered naturally from COVID-19 infections.
Merck has a history of successful vaccine development, so it was a bit surprising when they came so late to the COVID-19 vaccine arena. They chose a traditional approach of utilizing weakened viruses. The V590 leveraged technology from the company’s Ebola vaccine, and the V591 tech is based on a measles vaccine utilized in Europe. The company only finished recruiting volunteers for the Phase I study close to the end of 2020, while Pfizer-BioNTech and Moderna were at that time already reporting Phase III data and submitting packages to the U.S. Food and Drug Administration (FDA) for Emergency Use Authorization (EUA). Both companies’ COVID-19 vaccines are being dosed throughout the U.S. and Europe.