The Saudi count grows to 345, including 105 deaths, as a local medical conference is shelved.
Saudi Arabia reported 26 cases and Egypt its first, but new sequencing findings showed no major mutations.
Two research teams say they have identified antibodies against the novel virus.
Some have theorized about changes in the virus, but preliminary data show no mutations so far.
As the WHO suggests a slight change in spread, the ECDC calls for higher concern.
Testing of nasal and eye swabs of camels in Oman found 5 of 76 samples positive for Middle East respiratory syndrome coronavirus (MERS-CoV), and genetic sequencing showed that they were closely related to human viruses in the region
Experts say possibilities include a change in the virus and a seasonal pattern to transmission.
The WHO offered investigation help, with 33 more infections reported in Saudi Arabia and UAE.
Scientists found that camels in three widely separated African countries had MERS-CoV-like antibodies.
The Saudi MERS count surged by 37 cases and 6 deaths in 3 days, including 21 new cases in Jeddah's outbreak.
