Merck halts development of COVID-19 vaccine candidates due to poor immunity showings

Although well-tolerated, Merck’s two COVID-19 vaccine candidates — V590 and V591 — have been discontinued due to immune responses well below those provided by natural infection or other vaccines.

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

This decision resulted from phase one clinical studies, the results of which will be published in a peer-reviewed journal. As a result, the company has pivoted entirely to two investigational therapeutic candidates — MK-4482 and MK-7110 — instead. MK-4482, or molnupriravir, is being developed in collaboration with Ridgeback Bio.

The pair of therapeutics work in different ways, however. MK-7110 would be a first-in-class investigational recombinant fusion protein that modulates the inflammatory response to SARS-CoV-2, focusing its efforts on an immune pathway checkpoint. That therapeutic has already undergone a phase three study, the interim results of which showed a greater than 50 percent reduction in deaths or respiratory failure in those hospitalized with moderate to severe cases of COVID-19.

Molnupiravir, on the other hand, is an oral antiviral agent. It’s still under evaluation in phase 2/3 clinical trials both in hospitals and out-patient settings, but these should conclude in May.

For both medicines, results should be available in the first quarter of 2021 — the full results for MK-7110 and initial efficacy data for molnupiravir.