(CN) — As the Covid-19 death toll in the United States passes the grim milestone of 200,000, a mathematic analysis of U.S. cases shows that 31 states entered their second wave at the end of July — while 13 others were still in the first wave.
The notion of a second wave of the novel coronavirus, a phenomenon wherein a disease infects one group of people first, then infections appear to decrease but later increase in a different part of the population resulting in a second wave of infections, has been looming since the global pandemic began. And recently, there is speculation that a second wave is starting in Europe.
Some European countries are reporting a rapid rise in Covid-19 hospitalizations. Hospitalizations have doubled every eight days in the U.K., and parts of France have reported reaching capacity in their intensive-care units, CNN reported.
In a paper published Tuesday in the journal Chaos, mathematicians report a method to analyze Covid-19 cases for evidence of a first or second wave. The authors studied data from all 50 U.S. states plus the District of Columbia for the seven-month period from Jan. 21 to July 31, 2020.
After smoothing the raw daily case count to eliminate artificial peaks and drops, a numerical technique was used to find peaks and troughs. From this, the analysis's authors identified turning points for each state.
A turning point occurs when a falling curve surges upward or a rising curve turns downward. Only those sequences where the peak and trough amplitudes differ by a certain minimum were counted.
Thirteen states, including Georgia, California, and Texas, had increasing case numbers throughout the entire seven-month period and are considered to be still in their first wave. Thirty-one other states, including Florida and Ohio, exhibit sequences trough to peak to trough to peak — zero cases to a first peak, then another trough and peak. This is the signature of a second wave.
New York and New Jersey had completely flattened their curves by the end of July. The analysis confirms these two states experienced just one wave.
Study author Nick James points out this sort of analysis can be used to weigh the efficacy of states' Covid-19 responses.
“After an early first surge, Florida reduced restrictions and has since experienced a long and steep second surge,” he said. This contrasts with New York and New Jersey, who kept restrictions in place and have, so far, avoided a second wave.
Going further, study co-author Max Menzies said their analysis shows governments should never allow new cases to increase, nor reduce restrictions when case numbers have merely flattened.
“A true turning point, where new cases are legitimately in downturn and not just exhibiting stable fluctuations, should be observed before relaxing any restrictions,” he said.
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