Since Middle East respiratory syndrome coronavirus (MERS-CoV) was first identified in Saudi Arabia last year, it has infected 77 people, mostly in the Middle East and Europe. Forty of them - more than half - have died. But MERS is not yet a pandemic, according to a new study by the Institut Pasteur in Paris.
MERS, which causes fever, coughing and sometimes kidney failure, may have developed from a virus found in bats. It is similar to the SARS virus, which killed nearly 800 people around the world in 2003.
Using data from the known cases of MERS, the researchers found that, on average, someone with the disease is likeliest to infect at most, only one other person. SARS patients were likely to infect three others. That level of contagiousness made it a pandemic.
Although MERS is deadlier than SARS was, its lower level of contagiousness means that it may eventually fade away on its own.
However, the researchers call for continued surveillance and caution. They point out that SARS became more contagious over time, and that MERS could do the same.