Chris Murray, a University of Washington disease expert whose projections on COVID-19 infections and deaths are closely followed worldwide, is changing his assumptions about the course of the pandemic.

Murray had until recently been hopeful that the discovery of several effective vaccines could help countries achieve herd immunity, or nearly eliminate transmission through a combination of inoculation and previous infection. But in the last month, data from a vaccine trial in South Africa showed not only that a rapidly spreading coronavirus variant could dampen the effect of the vaccine, it could also evade natural immunity in people who had been previously infected.

"I couldn’t sleep” after seeing the data, said Murray, director of the Seattle-based Institute for Health Metrics and Evaluation. "When will it end?” he asked himself, referring to the pandemic. He is currently updating his model to account for variants’ ability to escape natural immunity and expects to provide new projections as early as this week.