As Covid-19 tears across the country, health experts have been calling for increased access to testing that will help track and contain the virus’s swift and often silent spread.

But some of the cheapest and most convenient diagnostic tools on the market might not perform as promised in a crucial contingent of the population, in which they were already being used: children, whose pint-size bodies might make the coronavirus more difficult to detect.

A small but growing body of evidence, some of which has not yet been published in a peer-reviewed scientific journal, suggests that some rapid tests for the coronavirus may falter in very young people, letting low-level infections slip by unnoticed.

Each week, good news about vaccines or antibody treatments surfaces, offering hope that an end to the pandemic is at hand.

And yet this holiday season presents a grim reckoning. The United States has reached an appalling milestone: more than one million new coronavirus cases every week. Hospitals in some states are full to bursting. The number of deaths is rising and seems on track to easily surpass the 2,200-a-day average in the spring, when the pandemic was concentrated in the New York metropolitan area.

Our failure to protect ourselves has caught up to us.