Why a negative Covid-19 test before Thanksgiving isn’t an all-clear

More frequent Covid-19 testing is one key to help end the pandemic. But as individuals, we can’t rely on testing alone to protect ourselves and others.

Take this recent example: Public health officials in New Zealand reported on a cluster of cases that likely spread aboard a long-haul flight. Yet the suspected index cases — the people who likely spread the virus to others — tested negative for the virus a couple of days before boarding their plane in Switzerland and thought they weren’t infected.

This goes to show: A...