US Giant Merck Ends Covid Vaccine After Poor Response

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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 long 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 V590 and V591 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.

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