Dive Brief:

• Merck & Co. will stop developing two experimental coronavirus vaccines after both produced disappointing results in early-stage testing, the large drugmaker said Monday.

• The two vaccines, known as V590 and V591, led to weaker immune responses in Phase 1 clinical trials than what’s been observed following natural infection as well as in studies of other coronavirus vaccines. Merck acquired one of its candidates through a buyout of privately held biotech Themis, and the other via a partnership with the nonprofit group IAVI.

• The surprising setback removes one of the world’s top vaccine developers from coronavirus research at a time when more shots are needed to reinforce early immunization efforts. Merck now plans to focus on testing two experimental COVID-19 treatments, including an antiviral drug that’s in a mid-stage trial.

Dive Insight:

Merck’s status as a leading company in infectious disease treatments made its early absence from coronavirus vaccine development all the more notable. While companies like Pfizer, AstraZeneca and Moderna each began human trials of vaccine candidates in the first six months of 2020, Merck didn’t even make its development plans public until last May, when it announced both the Themis and IAVI deals.

The company’s late entry reportedly followed a rejected overture to the University of Oxford, which eventually licensed its vaccine candidate to AstraZeneca.

With the IAVI and Themis vaccines, Merck bet on established technologies, which the company argued were more likely to succeed and result in a easier-to-distribute product. In doing so, Merck shied away from newer methods like messenger RNA. Though Merck has long been a Moderna partner and investor, for instance, the pharma didn’t back an mRNA-based vaccine. And CEO Ken Frazier publicly raised doubts about how quickly early movers would be able to prove out their vaccines.

Daria Hazuda, Merck’s head of infectious disease discovery, told Biopharma Dive in June that Merck was wary of pursuing a two-dose vaccine regimen during a pandemic. “Just think about global implementation, cost of goods and the burden on the healthcare infrastructure to do that in the midst of an epidemic,” Hazuda said at the time.

She also noted Merck’s preference for a shot with a faster immune response, claiming that’s why Merck favored vaccines based on modified viruses, which she said “tend to offer the greatest level of high level immunity really quickly.”

Merck wasn’t alone in its skepticism: Sanofi and partner GlaxoSmithKline, two other top vaccine makers, chose more traditional, protein-based technology for their vaccine, figuring it would lead to a more potent shot. (Sanofi has an mRNA-based vaccine in development through a deal with Translate Bio, but human testing hasn’t begun yet.)

But both Merck’s and Sanofi’s vaccines have now come up short. Sanofi and GSK are working on a different version of their shot after weaker-than-expected results in an early study — a monthslong delay.

Pfizer’s and Moderna’s vaccines, meanwhile, have proven strongly effective at preventing COVID-19, raising the bar for any developers that follow them.

Merck will now focus on developing COVID-19 treatments, which are still desperately needed as initial vaccine rollout goes slower than many had hoped. The company has two prospective drugs in testing. One, an oral antiviral called molnupiravir and licensed from Ridgeback Biotherapeutics, is being studied for both hospital and outpatient treatment. The other, acquired through Merck’s buyout of OncoImmune, is meant to tamp down an overactive immune response in more severe COVID-19.

Merck said it will share initial data from molnupiravir this quarter “if clinically meaningful.” Full results from a Phase 3 study of the OncoImmune drug are expected by the end of March, and the U.S. has already pre-ordered up to 100,000 doses.

Merck plans to publish results from the two vaccine trials in a peer-reviewed journal.