Merck & Co (MSD) has ended its COVID-19 vaccine programme after reviewing some disappointing phase 1 results for its candidates V590 and V591.
Although both V590 and V591 were generally well-tolerated in the phase 1 trials, immune responses for the candidates were inferior to those observed in recovered COVID-19 patients as well as those reported for other vaccines.
Merck did not disclose the exact response levels but the company is planning to submit the results for publication in a peer-reviewed journal.
The World Health Organization’s (WHO) document, ‘Considerations for Evaluation of COVID-19 Vaccines’, states: ‘To ensure that a widely deployed COVID-19 vaccine is effective, the primary efficacy endpoint point estimate for a placebo-controlled efficacy trial should be at least 50%’.
The COVID-19 vaccines from Pfizer/BioNTech and Moderna have yielded efficacy rates above 90% – coming in at 95% and 94.5%, respectively, with AstraZeneca/Oxford University’s COVID-19 vaccine coming in with a confirmed efficacy of 70.4%.
“We are grateful to our collaborators who worked with us on these vaccine candidates and to the volunteers in the trials,” said Dean 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, healthcare systems and communities,” he added.
On a more positive note, Merck will continue to advance clinical programmes for two novel therapeutics targeting SARS-CoV-2, the virus which causes COVID-19.
This includes a potentially first-in-class recombinant fusion protein known as MK-7110, which is designed to target a novel immune pathway checkpoint believed to be involved in the body’s inflammatory response to the novel coronavirus.
The second treatment, MK-4482 or molnupiravir, is an investigational oral antiviral candidate that Merck is developing with Ridgeback Bio.
The antiviral agent is already being evaluated in phase 2/3 clinical trials in hospital and outpatients settings, with a primary completion date set for May 2021.
In December, Sanofi and GlaxoSmithKline (GSK) also suffered a setback to their COVID-19 vaccine programme after their jointly developed candidate induced a low immune response in older adults.
As a result, the two companies have delayed the programme, rescheduling their previous timeline for the vaccine with a new plan to launch a phase 2b study in February 2021.
The phase 2b study will test an improved antigen formulation, after a recent challenge study in non-human primates showed that this new formulation could protect against lung pathology.