COVID-19 | 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.

However, 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...