Merck said in a statement posted on its website the decision to scrap the two vaccine candidates followed its review of findings from Phase 1 clinical studies. The studies showed that both candidates were generally well tolerated, but the immune responses were inferior to those seen following natural infection with Covid-19 and those reported for other Covid-19 vaccines.
Merck was late to join the race to develop a vaccine to protect against the virus, which has so far killed more than 2 million people worldwide and infected nearly 100 million.
U.S. regulators authorized Covid-19 vaccines from Moderna and partners Pfizer and BioNTech in December, and tens of millions of doses of both have so far been administered globally as governments around the world rush to vaccinate as many people as possible to lift damaging lockdowns.
Rivals Johnson & Johnson, AstraZeneca Plc and others are also working to develop safe and effective vaccines to protect against the virus.
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Merck still plans to submit the results of the Phase 1 studies for the two scrapped vaccine candidates for publication in a peer-reviewed journal, its statement said.
The company will now focus on two Covid-19 investigational medicines and other Covid-19 research, the statement added.
Reuters contributed to this report.