By Jared S. Hopkins 

Merck & Co. said Monday that it is halting development of its two experimental Covid-19 vaccines, after early clinical-trial data showed the shots generated disappointing immune responses against the virus.

Early-stage studies of the vaccines indicated they produced inferior immune responses in subjects given the shots compared with people who survived Covid-19 or took authorized Covid-19 vaccines, the company said.

The exit removes a major vaccine player from the constellation of firms seeking shots to curb the spread of the virus, as the few companies that have been able to bring shots to market struggle to meet heavy demand.

Kenilworth, N.J.-based Merck, one of the world's leading vaccine makers, said it would now focus on advancing two experimental Covid-19 drugs.

Merck said it expects test results for the pair of drugs in the coming weeks, and the company could ask regulators to authorize use if the results are positive.

"We're quickly informing society so that obviously we can refocus on therapeutics, but also so that some of the knowledge is shared with the broader community," Nick Kartsonis, who oversees Merck's vaccine clinical research, said in an interview.

Dr. Kartsonis said it was unclear why the shots weren't very effective, though they were safe. Merck didn't provide the study results, saying it would submit the findings for publication in a peer-reviewed medical journal.

Due to the discontinuation, the company said it would record an unspecified pretax charge in the fourth quarter of 2020.

Some 60 Covid-19 vaccines are in human testing, according to the World Health Organization, but regulators have only authorized a handful for general use, leaving limited supplies.

Many scientists and public-health experts placed high hopes on Merck, which pioneered vaccines that have become staples around the world, including the first to prevent mumps, chickenpox, rubella and shingles.

Yet Merck was slower than rivals to pursue Covid-19 vaccines. Chief Executive Ken Frazier and then-R&D chief Roger Perlmutter expressed concern about the years vaccine research usually takes, and that it would divert resources from thriving areas, such as cancer drugs, The Wall Street Journal reported in October.

Merck executives have also said they wanted to use vaccine technologies that have worked against other viruses, and that could be fashioned into a single-dose regimen.

The drugmaker discussed collaborating with the University of Oxford on its experimental vaccine, but university scientists and the U.K. government resisted a proposed deal, The Journal reported. Oxford ended up joining with AstraZeneca PLC.

In late May, Merck announced it was pursuing two Covid-19 vaccines, one as a result of the company's acquisition of Themis Bioscience and the other in partnership with the scientific-research organization IAVI.

The Themis vaccine uses a weakened version of the virus that causes measles to deliver coronavirus's spike protein to the immune system, helping trigger an immune response. Merck conducted a 260-person early-stage study to evaluate whether it worked safely against Covid-19.

Merck's second vaccine, developed with IAVI, employs the technology that is the basis for the drugmaker's Ebola virus vaccine, using a modified and weakened virus to carry the genetic instructions to teach cells to make a protein from the coronavirus. The vaccine was tested in a 252-person trial.

In reviewing the results from the early-stage studies for both vaccines, Merck wasn't encouraged when it looked at data for antibody production, including the neutralizing antibodies that play a key role preventing the virus from entering cells and replicating, Dr. Kartsonis said.

"It doesn't appear that our responses are numerically on par with what you would see either following natural infection or what we've been seeing" with vaccines from Pfizer Inc., Moderna Inc. or AstraZeneca, he said.

The vaccines from Pfizer, and its partner BioNTech SE, and Moderna are authorized for use in the U.S. AstraZeneca's shot has been cleared for use in the U.K. and certain other countries, though not the U.S.

The Pfizer-BioNTech and Moderna vaccines were more than 94% effective in late-stage trials, while the AstraZeneca-Oxford shot was at least 62% effective in some final-stage studies.

One of the experimental drugs Merck is working on would treat severe and critical Covid-19 patients. Merck acquired the drug via a $425 million acquisition of a company named OncoImmune. Merck expects results from a late-stage study by the end of March.

Merck signed a $356 million agreement with the U.S. government to supply the drug, should regulators give the treatment a green light.

The company's second Covid-19 therapy, called molnupiravir and developed with privately held Ridgeback Biotherapeutics LP, is under evaluation in hospitalized and outpatient Covid-19 patients. The companies expect late-stage trial data by the end of March, Merck said.

Having effective Covid-19 treatments remains important, especially as new variants emerge that may be able to thwart vaccines, Dr. Kartsonis said.

Write to Jared S. Hopkins at


(END) Dow Jones Newswires

January 25, 2021 06:59 ET (11:59 GMT)

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