Until 2020, few Americans needed to think about how viruses spread or how the human immune system works. The pandemic offered a painful crash course. Sometimes, it seemed that the science was evolving as quickly as the virus itself.

So The New York Times asked experts to revisit the nightmare. Of the most significant public health measures introduced during Covid, which have held up scientifically, and which turned out to be wrongheaded?

The question is particularly important now, because pandemics that could upend American lives are inevitable. One candidate has already surfaced: bird flu.

Perhaps the biggest lesson learned, several experts said, is that recommendations during any pandemic are necessarily based on emerging and incomplete information. But during Covid, federal agencies often projected more confidence in their assessments than was warranted.

Next time, the scientists said, officials should be more forthright about the uncertainties and prepare the public for guidance that may shift as the threat comes into clearer focus.

Rather than promote preventive measures as infallible solutions, they should also acknowledge that no single intervention is perfect — though many imperfect measures can build a bulwark.