The total number of reported deaths linked to the disease topped 770,800 on Saturday, Johns Hopkins data show. This puts the pandemic-long total at more than twice the 385,343 Covid-19 deaths recorded last year, according to the most recent death-certificate data from the Centers for Disease Control and Prevention.

The spread of the highly contagious Delta variant and low vaccination rates in some communities were important factors, infectious-disease experts said. The milestone comes as Covid-19 cases and hospitalizations move higher again in places such as New England and the upper Midwest, with the seven-day average for new cases recently closer to 90,000 a day after it neared 70,000 last month…

The 2021 U.S. death toll caught some doctors by surprise. They had expected vaccinations and precautionary measures like social distancing and scaled-down public events to curb the spread of infections and minimize severe cases. But lower-than-expected immunization rates as well as fatigue with precautionary measures like masks allowed the highly contagious Delta variant to spread, largely among the unvaccinated, epidemiologists say.

“Heading into this year, we knew what we needed to do, but it was a failure of getting it done,” said Abraar Karan, an infectious-diseases doctor at Stanford University.