The country’s vaccine rollout has sped up since the first doses were administered in December, recently reaching a rolling average of more than three million doses per day. And new U.S. cases trended steeply downward in the first quarter of the year, falling by almost 80 percent from mid-January through the end of March.
But during that period, states also rolled back virus control measures, and now mobility data shows a rise in people socializing and traveling. Amid all this, more-contagious variants have been gaining a foothold, and new cases are almost 20 percent higher than they were at the lowest point in March.
Michigan has seen the sharpest rise in cases in the last few weeks. B.1.1.7 — the more transmissible and more deadly variant of the coronavirus that was first discovered in the United Kingdom — may now make up around 70 percent of all of the state’s new cases, according to the Helix data.
Some experts estimate 70 to 90 percent of the population would need to acquire resistance before transmission would substantially slow. As of April 5, less than 20 percent of the U.S. population has been fully vaccinated against the virus.