Threat: MERS-CoV has a high mortality rate — more than 40 percent. For comparison, its relative, SARS-CoV, killed less than 10 percent of people infected during a 2002-03 global outbreak.
Body count: Since claiming its first known human victim in 2012, MERS-CoV has infected more than 144 people, mostly in Saudi Arabia, killing 62.
Wily adversary: In September, a genome sequencing study of MERS-CoV revealed that the virus did not follow mathematically predicted patterns of transmission; it likely has transmission routes other than sick individuals, such as asymptomatic humans or an as-yet-unknown domestic animal host.
Bullet dodged: Public health officials feared more than 2 million Muslims from around the world who traveled in October to Saudi Arabia’s Mecca for the annual haji pilgrimage would provide a target-rich environment for a MERS-CoV outbreak. The virus, however, appears to be laying low. For now.
[This article originally appeared in print as "Hunting a Killer Virus."]