The World Health Organization warned on Tuesday that the novel coronavirus was a “very grave threat” for the planet as it hosted the first major conference on fighting the epidemic. About 400 scientists were taking part in the two-day international meeting in Geneva which will review how the virus is transmitted and possible vaccines against it.”With 99 percent of cases in China, this remains very much an emergency for that country, but one that holds a very grave threat for the rest of the world,” WHO head Tedros Adhanom Ghebreyesus said at the start of the meeting.