Closing the knowledge gaps on MERS: three and half years since its detection, what have we learnt and what needs to be done urgently? (Editorial).

The Middle East respiratory syndrome coronavirus (MERS-Cov), first detected in 2012, continues to cause health concerns owing to the grave uncertainties that have surrounded the virus since it emerged. Three and half years after the first known human infection was detected, cases continue to be reported every month, over 85% of which have been from Saudi Arabia and other countries in the Arabian Peninsula. Despite its low levels of transmission, the virus presents an uncertain future as a number of critical knowledge gaps on the source and route of transmission have hindered the global response to this emerging infection.