Jan. 25 (UPI) -- Drugmaker Merck and France's internationally renown Pasteur Institute both announced on Monday that they're ending development of three separate potential coronavirus vaccines.
The pharmaceutical company said research has been terminated for its V590 and V591 vaccine candidates, because the immune responses it produced in first-stage trial volunteers were inadequate.
"In these studies, both V590 and V591 were generally well tolerated, but the immune responses were inferior to those seen following natural infection and those reported for other SARS-CoV-2/COVID-19 vaccines," Merck said in a statement.
"We are resolute in our commitment to contribute to the global effort to relieve the burden of this pandemic on patients, health care systems and communities," added Merck President Dr. Dean Li.
Merck also said it will continue development for two other vaccine candidates, MK-4482 and MK-7110. The former is being co-developed by Ridgeback Bio.
Although it's ending development for the V590 and V591 candidates, Merck said it will still publish first-stage clinical trial data for peer review.
"The COVID-19 pandemic underscores the need for our company and our industry to continue to invest in research to address threats to health security," the company said.
Merck has been working toward a coronavirus vaccine since at least last May. Several other pharmaceutical companies are also developing potential vaccines, including Johnson & Johnson, AstraZeneca and Novavax.
So far, two vaccines -- from Moderna and Pfizer-BioNTech -- have been approved for use in the United States.
Researchers are also examining whether the existing vaccines are effective against mutated strains of COVID-19, which have recently emerged in several countries.
Some experts believe the current vaccines will also be effective in blocking new variants -- although Dr. Anthony Fauci, the top infectious diseases expert in the United States, said last week that they might not offer quite as much protection against mutations as they do for the original strain.
Also Monday, France's Pasteur Institute announced that it's ending a vaccine it had been developing with Merck after disappointing test results.
Its vaccine had been based partly on the measles vaccine virus.
"The decision not to pursue the development of the vaccine candidate based on the measles vaccine virus was made following an analysis of the intermediate results obtained from Phase I trials, which began in August 2020," the institute said in a statement.
"This decision in no way affects [our] continued research on two other vaccine candidates based on different methodologies. The first, administered by nasal route, is being developed with the biotech company TheraVectys," the institute added. "The second is a DNA vaccine candidate. These two candidates are currently in preclinical phase."