The number of deaths, however, continue to decline — potentially a sign that mass vaccinations are beginning to protect older Americans and other highly vulnerable populations.
“These trends are pointing to two clear truths,” Dr. Walensky said. “One, the virus still has hold on us, infecting people and putting them in harm’s way, and we need to remain vigilant. And two, we need to continue to accelerate our vaccination efforts and to take the individual responsibility to get vaccinated when we can.”
B.1.1.7, the first variant to come to widespread attention, is about 60 percent more contagious and 67 percent more deadly than the original form of the coronavirus, according to the most recent estimates. The C.D.C. has also been tracking the spread of other variants, such as B.1.351, first found in South Africa, and P.1, which was first identified in Brazil.
The percentage of cases caused by variants is clearly increasing. Helix, a lab testing company, has tracked the relentless increase of B.1.1.7 since the beginning of the year. As of April 3, it estimated that the variant made up 58.9 percent of all new tests.
That variant has been found to be most prevalent in Michigan, Florida, Colorado, California, Minnesota and Massachusetts, according to the C.D.C. Until recently, the variant’s rise was somewhat camouflaged by falling infection rates over all, leading some political leaders to relax restrictions on indoor dining, social distancing and other measures.