Virus mutations aren’t slowing down. New omicron subvariant proves it.

During those terrifying early days of the pandemic, scientists offered one piece of reassuring news about the novel coronavirus: It mutated slowly. The earliest mutations did not appear to be consequential. A vaccine, if and when it was invented, might not need regular updating over time.

This proved overly optimistic.

The coronavirus, SARS-CoV-2, has had billions of chances to reconfigure itself as it has spread across the planet, and it continues to evolve, generating new variants and subvariants at a clip that has kept scientists on their toes. Two-and-a-half years after it...