How bad will omicron be? Scientists won't really know for months

In a virus that has already killed 5.2 million people across the globe, 50 or so new mutations sound like a nightmare for humanity. But in the age-old battle between microbes and mankind, that many genetic changes can turn the tide in any direction.

The next chapter of the pandemic could feature an omicron variant that spreads more readily than delta, blows past the defenses of a fully vaccinated immune system, and, like its coronavirus cousin that causes Middle East respiratory syndrome, kills more than one-third of those who get it. That worst-case scenario would be an unfathomable disaster, said Dr. Bruce Walker, an immunologist and founding director of the Ragon Institute in Cambridge, Mass.

At the other end of a wide spectrum of possibilities, humanity could catch a break. Omicron could