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5 charts that tell the story of COVID-19 in Mass.

Coronavirus testing in Dedham last month.
Coronavirus testing in Dedham last month.Pat Greenhouse/Globe Staff/file

How is the state doing in its battle against the coronavirus?

Some experts say it’s time for caution, but Massachusetts is moving ahead with reopening in many cities and towns.

These five charts tell the story of a state that, with a lot of sacrifice, crushed the virus earlier this year — and is now seeing the virus creep back again.

In this first chart, the number of cases reported per day is shown since the beginning of the pandemic, along with a seven-day average. Reopening phases are also shown. The chart shows a mountain of cases per day in the spring as a terrified state hunkered down at home, a decrease in cases to a low point around late June, and then a slow rise in cases again.

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The second chart is more worrisome. It takes a look at the same metrics as the first but begins when the case count hit its low point. It highlights the virus’s rise since then, though the numbers haven’t climbed anywhere near the levels they reached in the spring.

The third chart shows the two ways the state has calculated the seven-day average test positivity rate. The state currently highlights in its daily reports the rate in blue. It is calculated by dividing the number of positive cases by the number of tests administered. The overall number of negative tests each day has dramatically increased due to a relatively recent surge in the repeat testing of asymptomatic people, such as students on college campuses. And that has played a role in driving this rate down.

The state previously highlighted the rate in red, which removes the repeated tests from the equation. It is calculated by dividing the number of positive cases by the number of people tested. Some experts say that this method is a better indicator of how hard the pandemic is hitting.

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The chart begins in mid-August when the state changed the way it calculated the numbers. At the time, the two numbers were fairly close together. Now they have diverged sharply. (Note: the state does offer in its daily reports a single-day rate of positive cases per people tested, but not the seven-day average.)

The fourth chart shows the results of tests of the wastewater at the Massachusetts Water Resources Authority’s plant on Deer Island. The tests for traces of the virus are made as part of a pilot project to see if they can serve as an early-warning system. The tests show the same pattern of a marked spike this spring, a low point this summer, and a gradual rise since then. The test results are broken down by northern and southern sections of the MWRA system.


The UMass ensemble model sees coronavirus cases declining slightly in the weeks ahead, though the numbers could range higher or lower.
The UMass ensemble model sees coronavirus cases declining slightly in the weeks ahead, though the numbers could range higher or lower.Reich Lab/UMass


The fifth chart shows the University of Massachusetts' weekly ensemble model of where the pandemic will go next for Massachusetts. The chart shows cases in the past as well as a four-week prediction for the future. The past cases show a familiar curve, with cases sharply rising, steeply dropping, and then edging up again.

As for future cases, the model, as of last week, took an optimistic view. It predicted that the weekly number of cases would decline slightly up to Oct. 24, though researchers note that the actual results could range higher or lower than their predictions. The range of possible outcomes is shown in the purple-shaded area.

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Martin finucane can be reached at martin.finucane@globe.com. John Hilliard can be reached at john.hilliard@globe.com. Dasia Moore can be reached at dasia.moore@globe.com. Follow her on Twitter @daijmoore.