When last we checked in on the elusive disease MERS—Middle East Respiratory Syndrome, caused by a virus related to the cause of the worldwide SARS epidemic in 2003—it had been brewing in the Gulf states for three years, but was triggering international alarm because of an outbreak in Korea.

That was in June. There has not been a case of MERS in Korea since July. But rather suddenly, the virus has picked up activity in the country where it got started, the Kingdom of Saudi Arabia. And that’s a concern, because in a month, Saudi Arabia will host millions of temporary visitors from all over the world, making the obligatory pilgrimage known as the hajj.

Earlier in the MERS outbreak, there was international criticism (some of