Scientists have unraveled the genetic code of the common cold — all 99 known strains of it, to be exact. But don't expect the feat to lead to a cure for the sniffling any time soon. It turns out that rhinoviruses are even more complicated than researchers originally thought.

In fact, the genetic blueprints showed that you can catch two separate strains of cold at the same time — and those strains then can swap their genetic material inside your body to make a whole new strain.

It's why we'll never have a vaccine for the common cold, said biochemist Ann Palmenberg of the University of Wisconsin-Madison, who led the three teams that assembled the family tree of the world's rhinoviruses.

"No vaccine, but maybe a drug," she said.

Why? The outside of these viruses — the part your body's immune system must recognize — are hugely variable, making it hard to envision a vaccine that would work against very many strains. But the inside components, what Palmenberg calls the guts of the virus, are remarkably similar from strain to strain, offering targets for therapy.

Adults typically get two to four colds a year, while schoolchildren may get as many as 10. But they do more than cause a runny nose. Rhinoviruses can trigger asthma attacks and play a role in sinusitis, certain ear infections and pneumonia.

Yet these viruses are remarkably mysterious for such a common bug. It was only in the past two years that scientists discovered there aren't two main groups of the viruses but three_ and this new "Group C" collection is nasty, tending to lodge deep in the lungs, Palmenberg said.

Wisconsin researchers paired with teams at the University of Maryland and J. Craig Venter Institute to decipher the genetic sequences of all known Group A and B rhinovirus strains and see how they're related to the newer Group C strains.

The resulting cold family tree, reported online Thursday by the journal Science, organizes human rhinoviruses into 15 distinct branches that evolved over time. Now the hunt is on to define the viral commonalities on each branch, in the quest for anti-cold drugs.