Helen Branswell is one of my favorite sources on global public health and pandemic disease. She's got a guest post at Scientific American blogs that explains what we do know about MERS, and why the lack of information is such a big problem.
The new virus was first isolated in June 2012. But its existence came to the world’s attention only weeks before last October’s hajj, when an Egyptian infectious diseases specialist who had been working in Saudi Arabia’s second largest city, Jeddah, reported that he had treated a man who died from an infection caused by a new coronavirus. Whether MERS has or can gain the capacity for sustained person-to-person spread is unknown.
... Infectious disease experts are aghast that this late into MERS’s spread the world still has no idea what puts people at risk of infection, how long the incubation period is, when people are contagious or whether there are mild cases that are being missed because surveillance is focused on finding sick people in hospitals. They put the problem squarely at the feet of the Kingdom of Saudi Arabia (KSA), which accounts for 41 of the 55 infections to date.