Published: 13:23 EDT, 22 September 2020 | Updated: 16:48 EDT, 22 September 2020

Scientists have developed a mathematical model to determine whether or not US states are in a ‘second surge period’ of coronavirus infections.

Researchers from the University of Sydney, in Australia, looked at data and determined any state with a ‘second spike’ that is less than one-fifth of the first is not a true second wave because it is too small.

Using this methodology, they established that, by the end of July, at least 31 states such as Florida, Ohio and Pennsylvania were in their second surges.

About 13 states, including California, Texas and Georgia, had seen infection rates merely flatten for a bit, and not track downward, so they were still in their first waves.

Meanwhile, New York and New Jersey had completely managed to flatten their respective curves, and their first surge was ‘completely over’ with no second surge in sight.

The team says the findings can help local and state lawmakers determine when to ease restrictions by spotting the difference between stable or insufficiently declining infection rates and rates on a downward trajectory.

Scientists have developed a mathematical model to determine whether or not US states are in a ‘second surge period’ of coronavirus infections. Pictured: Bodies are moved to a refrigerator truck serving as a temporary morgue outside of Wyckoff Hospital during the coronavirus pandemic in Brooklyn, New York, April 4

STILL IN FIRST WAVE: Thirteen states, such as Georgia (left) and California (right), were found be in their first waves. This is because these states had rising case numbers from January to July with no significant downward trajectories

STILL IN FIRST WAVE: As of August, Texas (left) was still in its first wave despite a short flattening of cases from April to June. North Carolina (right) has been on a steady, upward climb with no flattening cases

STILL IN FIRST WAVE: Arkansas (left) was found to still be in its peak despite a flattening over Spring 2020. Mississippi (right) is also in its first surge with a sharp upward trajectory since early June

‘In some of the worst performing states, it seems that policymakers have looked for plateauing or slightly declining infection rates,’ said co-author Dr Nick James, a PhD student in the School of Mathematics and Statistics at the University of Sydney.

‘Instead, health officials should look for identifiable local maxima and minima, showing when surges reach their peak and when they are demonstrably over.’

For the study, published in the journal Chaos, the team looked at data from all 50 US states and the District of Columbia from January 21, 2020 to July 31, 2020.

Researchers adjusted raw daily case totals to account for low totals that typically occur over weekends and negative counts on day that counties are correcting errors.

After the data is smoothed, the mathematical model looks for peaks and troughs, and identifies a turning point. 

NOW IN SECOND WAVE: At least 31 states, including Florida (left) and Ohio (right) were found to be their second surges. These states had an initial surge followed by declining infections and then a second surge

NOW IN SECOND WAVE: Connecticut (left) had its first wave last from mid-April to July, but entered its second eave in August. Minnesota (right) saw its first wave last from mid-May to late June, but experienced a second wave in August 

NOW IN SECOND WAVE: Massachusetts (left) saw its first wave last from late April to July and experienced a second wave in August. Iowa (right) had its first wave from early May to early June and entered a second wave in August

A turning point was identified as the trajectory of rising curves suddenly dropping or downward curves spiking.

Peak highs and trough lows have to vary by a certain amount as well, and graphs were created for 18 states.

For example, a second wave with less than one-fifth the number of cases in the first does not qualify as a second wave because it is simply too small, the researchers say

Thirteen states, including California, Georgia, Mississippi, North Carolina and Texas, had rising case numbers throughout the entire seven-month period. 

Because of this, they are considered to be still in their first wave with a single increasing infection surge.

NOW IN SECOND WAVE: Idaho (left) saw its first wave last from early April to early May and experienced a second wave in August. Pennsylvania (right) had its first wave from late April to late June and entered a second wave in August

WAVE OVER: New York (left) and New Jersey (right) had managed to flatten their curves after their first wave and were found to not be in any surge

COMING DOWN FROM WAVES: Arizona (left) is coming down from its first wave, which peaks in early July before ending in August. Maine (right) is coming down fro it second wave, which lasted from late May to early August

Researchers assigned 31 states, including Florida, Ohio and Pennsylvania, the sequence TPTP, meaning zero cases to a first peak, then another trough and peak. 

This means these states are currently in their second waves, which is an initial surge followed by declining infections and then a second surge.

Meanwhile, New York and New Jersey flattened their respective curves by the end of July, and therefore experienced just one wave each.

The remaining four states, Arizona, Utah, Maine and Vermont, are still coming down from their first surges (the former two states) and second (the latter two states) surges.  

‘It is an analytical tool that should assist policymakers determining demonstrable turning points in COVID infections.’ 

Co-author Dr Max Menzies, from the Yau Mathematical Sciences Center at Tsinghua University in Beijing, said the analysis shows how reducing restrictions when curves have merely flattened, and not gone down, can lead to a deadly second surge.

”The real moral of this paper is that COVID-19 is highly infectious and very difficult to control,’ he said.

‘A true turning point, where new cases are legitimately in downturn and not just exhibiting stable fluctuations, should be observed before relaxing any restrictions

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Coronavirus, U.S. state

World news – GB – Model shows which US states are in a second wave of coronavirus

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