Researchers at two California universities say they may be close to finding the elusive cure for the common cold. The secret, they say, lies in humans, not the virus itself.

Stanford Medicine, working in conjunction with the University of California-San Francisco, says disabling a single, apparently non-critical protein in humans may stop viruses from replicating. Researchers say this works in viruses that are responsible for half of all common colds and has worked to stop viruses associated with asthma, encephalitis and polio.

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Stanford Medicine says there are roughly 160 known types of rhinovirus infections, which leads to about half of all colds. That's why you can get two or more colds, one right after the other. They can also mutate often, making them very drug resistant.

Researchers say they stopped a broad range of enteroviruses, including rhinoviruses, from replicating inside human cells by disabling a protein in the mammalian cells that all enteroviruses appear to need in order to replicate. 

The findings were made in both human cell cultures and in mice, Stanford Medicine said.

“Our grandmas have always been asking us, ‘If you’re so smart, why haven’t you come up with a cure for the common cold?’” Jan Carette, Stanford associate professor of microbiology and immunology, said in a press release. "Now we have a new way to do that.”

The cold isn't cheap. A 2003 University of Michigan study found that the common cold costs the U.S. economy $40 billion per year due to health care costs and lost productivity.

The Stanford-UCSF study is published in the journal Nature Microbiology.