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Time to Reach Each Million COVID19 Case Milestone

The first patient in the United States with COVID19 was diagnosed in Seattle on January 21, 2020. New York and the West Coast became the most affected regions, but outbreaks began surfacing elsewhere in vulnerable settings like nursing homes, prisons and meat packing plants. National stay-at-home orders went into effect in mid to late March around the country.

The average number of new cases per day in the United States peaked at 31,000 on April 10 and then slowly declined over the next 80 days to reach a plateau of approximately 21,000 per day in early June. Hospitalizations began leveling off through mid-April and then slowly declined. Deaths leveled off late April through early May and then began to decline in June.

Lockdowns caused more than 26 million Americans to become unemployed, and many governors were impatient to ease restrictions despite warnings from public health experts that it was too early. Most states began to lift restrictions at the end of April, or the start of May. Many states never enforced full lockdowns and still had a high number of daily new cases when they reopened. Georgia, Florida, Texas, Alabama, Kansas, Arizona, Mississippi, North Carolina, Wisconsin, Utah and others all reopened while cases were still rising.  

Sun Belt states, in particular, began experiencing serious outbreaks following Memorial Day. By the week of June 11, daily COVID19 cases began trending upward and continued increasing for seven consecutive weeks. From early June to mid-July, the number of confirmed COVID19 cases increased 215 per cent. On July 16, the United States reported a record number of 77,255 new daily. Instead of just one or two major epicenters, there were now multiple epicenters throughout the United States. Some of the highest positive rates were reported by Arizona at 24%, Florida and Nevada at 19%, and Idaho and Alabama at 18%. A plateau of 50,000 new daily cases was established during August.

After some Sun Belt states introduced mitigation measures, the number of COVID19 cases declined to about 34,000 by the beginning of the Labor Day weekend on September 5. However, within three weeks after the holiday, daily cases increased by 30% to 44,000. Clusters of cases also began to appear across the country in September as college campuses reopened. Twenty-one states had positive test rates ranging between 10.6% and 25.5%.

By October, Upper Midwest, Great Plains and Western states, that had previously been mostly spared, started reporting major outbreaks. In November, most states reported record-high case counts and greater demand for hospital beds. Several states set records for single-day fatalities.

Over the past two weeks, the seven-day average for new cases has jumped from fewer than 90,000 a day to 150,000 a day. Since October 16, COVID19 cases have begun exhibiting exponential growth. One way to visualize exponential growth is to look at the number of days required to reach one million cases. The following table summarizes the number of days it took in the United States to reach each successive million case milestone.

 

As can be seen it took 99 days to reach the first million COVID19 cases on April 28. The number of days decreased by nearly 50% between the first and second million and the second and third million cases. By late July and early August, the interval decreased to a low of 16 to 17 days and then plateaued at 22 to 24 days from the end of August to mid-October. That changed in mid-October, when the virus began surging again across much of the country. It took only 6 days to increase from 10 to 11 million cases and 7 days to increase from 11 to 12 million.

Because of the combination of the onset of winter, fatigue with preventive measures, holiday travel and gatherings and the patchwork of responses across all 50 states, the rate of new COVID19 cases is expected to escalate even faster.