The United States lost more than 17,000 people to COVID-19 last week, the largest number since the beginning of the global pandemic, with North Dakota, South Dakota and Iowa reporting the most deaths per capita in the past seven days.

Even as the first Americans were given the newly approved Pfizer/BioNTech coronavirus vaccine on Monday, health officials warned that infections will continue to rise in the coming weeks as families gather for the holiday season.

Deaths increased 12% in the week ended Dec.13 to a total of about 300,000 since the start of the outbreak, according to a Reuters analysis of state and county reports.

More than half of U.S. states have enacted new lockdown restrictions as many hospital intensive care units are nearly full. The University of Washington’s Institute for Health Metrics and Evaluation has projected that COVID-19 deaths will exceed 500,000 by April 1.

The number of new COVID-19 cases rose 15% to almost 1.6 million last week, including a backlog of almost 65,000 cases cases reported by Texas. Even excluding the backlog, the number of new infections last week hit a record high.

Rhode Island, Tennessee and Ohio had the highest new cases per capita in the country last week, according to the Reuters analysis.

Across the United States, 12% of tests came back positive for the virus, up from 10.5% the prior week, according to data from The COVID Tracking Project, a volunteer-run effort to track the outbreak. Out of 50 states, 32 had a positive test rate of 10% or higher. The highest rates were in Iowa and Alabama at 50%.

The World Health Organization considers positive test rates above 5% concerning because it suggests there are more cases in the community that have not yet been uncovered.