Merck Shuts Down Covid Vaccine Program After Lackluster Data

Merck & Co. is discontinuing development of its two experimental Covid-19 vaccines after early trial data showed they failed to generate immune responses comparable to a natural infection or existing vaccines.

The U.S. drug giant, which has a history of successfully developing vaccines, had adopted a different strategy from rivals Pfizer Inc., Moderna Inc. and Johnson & Johnson, using a more traditional approach of focusing on shots based on weakened viruses. One, called V590, borrowed technology from Merck’s Ebola inoculation, while the other, V591, is based on a measles vaccine used in Europe.

Both were laggards in the vaccine-development race. Merck finished recruiting the first participants for early-stage safety studies near the end of 2020, when front-runners Pfizer and Moderna were preparing to report late-stage data on their shots’ effectiveness. Merck received interim results from its trials this month.

The results were “disappointing, and a bit of a surprise,” said Nick Kartsonis, senior vice president of clinical research for infectious diseases and vaccines at Merck Research Laboratories. Both shots generated fewer neutralizing antibodies to halt infection than other Covid-19 vaccines, and produced inferior immune responses compared with people who had naturally contracted the coronavirus.

“We didn’t have what we needed to be able to move forward,” Kartsonis said in an interview Sunday. After evaluating the data, Merck’s senior leadership decided to discontinue the programs and divert resources to the company’s efforts to develop Covid-19 treatments.

Merck fell as much as 1.1% as of 9:50 a.m. Monday in New York. The shares lost 9.7% over the past 12 months through Friday’s close.

While Merck’s vaccines weren’t expected to be part of the initial immunization push in the U.S., the development comes amid heightened anxiety over vaccine supplies and a sluggish pace of injections. The emergence of new variants of the coronavirus has also raised questions about whether the shots that have been cleared will lose effectiveness as the pathogen mutates.

The failure of Merck’s candidates will also leave it locked out of a market that could eventually be dominated by two of its historic U.S. rivals. Pfizer was the first drugmaker to gain authorization for a Covid vaccine in the U.S., followed closely by Moderna. Johnson & Johnson is expected to publish data in the coming weeks on its vaccine’s efficacy and apply for an emergency-use authorization.

Neither of Merck’s candidates was among the six vaccines in the U.S.’s Operation Warp Speed portfolio, though its leadership watched them closely. The drugmaker and its development partner on V590, the International AIDS Vaccine Initiative, did receive some research funding from the government. Its second candidate, V591, relies on technology first developed by France’s Institut Pasteur. Both of the single-dose candidates were well tolerated in early human studies.

Kenilworth, New Jersey-based Merck will record a charge for the fourth quarter of 2020 for costs related to halting the programs. It didn’t disclose the amount of the charge Monday. The early-stage trial results will be submitted to a peer-reviewed medical journal.

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