Jan. 24 marks the one-year anniversary of a momentous but largely unnoticed event in the history of the Covid-19 pandemic: the first published report of an individual infected with the novel coronavirus who never developed symptoms. This early confirmation of asymptomatic infection should have set off alarm bells and profoundly altered our response to the gathering storm. But it did not. One year later we are still paying the price for this catastrophic blunder.

At least one of three people infected with SARS-CoV-2, the virus that causes Covid-19, do not develop symptoms. That’s the conclusion of a review we just published in the Annals of Internal Medicine. It summarizes the results of 61 studies with more than 1.8 million people.

But during much of the pandemic, fierce resistance — and even outright denialism — in acknowledging this not-so-typical disease pattern led to ineffective testing practices that allowed the pandemic to spin out of control.