In the U.S., COVID-19 cases in the Northeast are increasing again, which has some people worried about yet another surge.

This is also one of the most heavily vaccinated parts of the country. While the COVID-19 vaccines have been very effective at stopping hospitalization and death, it’s now clear they haven’t ended the pandemic.

And yet the scientists I spoke with in the early part of 2021 were nearly unanimous in thinking they would end the pandemic through herd immunity. Why did they get it so wrong?