LONDON—The U.K. appears to have passed the peak of the latest wave of Covid-19 caused by Omicron, a promising sign that the highly transmissible variant’s impact may be brief, if intense, and fueling optimism that the pandemic may be waning.

Scientists say British data offer encouraging signs for countries behind the U.K. in the Omicron wave—such as the U.S.—that the variant is echoing the pattern it followed in South Africa, where cases rose rapidly over the course of just over a month, before falling back.