Following a review of findings from phase 1 clinical studies, Merck has decided to discontinue the development of 2 coronavirus disease 2019 (COVID-19) vaccine candidates, V590 and V591.

While both candidates were found to be generally well tolerated, results from the studies showed immune responses that were inferior to those seen after natural infection or those reported with other COVID-19 vaccines. Additional data from these trials will be submitted for publication in a peer-reviewed journal.

“We are grateful to our collaborators who worked with us on these vaccine candidates and to the volunteers in the trials,” said Dr Dean Y. Li, president, Merck Research Laboratories. “We are resolute in our commitment to contribute to the global effort to relieve the burden of this pandemic on patients, health care systems and communities.”

The Company is currently investigating the efficacy and safety of 2 drug candidates, MK-7110 and MK-4482 (molnupiravir), for the treatment of COVID-19. MK-7110 is a potential first-in-class investigational recombinant fusion protein that modulates the inflammatory response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is currently being assessed in a phase 3 trial in hospitalized patients with moderate to severe COVID-19. Full study results are expected in the first quarter of 2021.

MK-4482 (molnupiravir) is an investigational oral antiviral agent that is being developed in collaboration with Ridgeback Bio. It works by inhibiting the replication of multiple RNA viruses including SARS-CoV-2 and is currently being assessed in phase 2/3 trials for the treatment of patients with COVID-19 in both hospital and out-patient settings. Initial efficacy data from the clinical trials are expected in the first quarter of 2021.


Merck discontinues development of SARS-CoV-2/COVID-19 vaccine candidates; continues development of two investigational therapeutic candidates. [press release]. Kenilworth, NJ: Merck; January 25, 2021.