Spanish researchers said Tuesday that they have created a mutated version of the deadly Middle East Respiratory Syndrome (MERS) coronavirus that could be used as the basis for a safe and effective vaccine.

The mutant MERS virus, called rMERS-CoV-E, is capable of infecting a cell, but is deprived of the ability to spread to other tissues and cause disease, researchers reported in the U.S. open-access online journal mBio.

"The injected vaccine will only replicate in a reduced number of cells and produce enough antigen to immunize the host," co- author Luis Enjuanes of the Autonomous University of Madrid said in a statement.

"It cannot infect other people, even those in close contact with a vaccinated person," he said.

In their study, the researchers synthesized an infectious clone of the MERS virus genome and then inserted the synthesized viral chromosome into a bacterial artificial chromosome, which allowed them to mutate several of its genes, one by one, to study the effects on the virus' ability to infect, replicate, and re-infect cultured human cells.

They found that mutations in the so-called envelope protein enabled the virus to replicate its genetic material, but prevented the virus from propagating, or infecting nearby cells.

When the virus is administered to a person for vaccination, this person will not be able to provide the envelope protein to the defective virus, so the virus will die off after producing antigens to train the human immune system to fight a MERS virus infection, the researchers said.

The researchers described the modified virus as being "a very promising vaccine candidate," but cautioned that more work remains before they can start clinical trials.

MERS was first described in September 2012 and continues to spread. So far, more than 110 human cases have been reported worldwide while 54 of them have been killed. Presently, there is no effective cure for it.

Last week, U.S. researchers reported a combination of two drugs, routinely used together to treat viral diseases such as hepatitis C, has shown promise in treating the MERS virus in macaque monkey models. Endi

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