A variant even more dangerous than the contagious delta currently circulating.
"The fewer people who are infected, the less lottery tickets it has and the better off we're all going to be in terms of generating the variants," he said, adding that variants are even more likely to emerge in people with weakened immune systems who harbor the virus for a long time.But some experts say children played a significant role this year spreading contagious variants such as alpha and delta.
If a variant 50% more transmissible than delta showed up in late fall, 860,000 cases would be averted, "a big impact," said project co-leader Katriona Shea, of Pennsylvania State University.
Stuart Campbell Ray, an infectious disease expert at Johns Hopkins University, said it may be intrinsically more infectious, or it may be evading at least in part the protection people get from vaccines or having been infected before.
"But there's also very good and growing evidence that delta is simply more fit, meaning that it's able to grow to higher levels faster than other variants that are studied.
"We have many lineages of delta that are circulating in many places with no clear winners," Ray said, adding that it's hard to know from genetic features which might have an edge, or which nondelta variants might dethrone delta.