COVID Odyssey: NZ New Year Fear 25 Post #952~ COVID-19 NZ~ Calculating Re over two cycles using Goal Seek

We want to estimate Re and hence Ro and COVID-19 spread when the period of infection is over two five day cycles.

We have weights w1 for Cycle 1 and w2 for Cycle 2 where w1 + w2 = 1 or
w2 = 1 – w1.

Let C be the number of new cases in a five day period (New in Column D ). These new cases are spread over two cycles (two five day periods) with:

• w1*C cases occurring in the current cycle; and
• w2*C cases occurring in the next cycle

For definitions and background see the bottom of this post.

We start with case numbers from the first outbreak of COVID-19 in New Zealand in 2020 (see the bottom of the image):

We set cell E9 to the total case numbers on 26 March (283).

We also set cell D12 to cell D30/10.

We use Goal Seek to set E10 to 0 by changing cell E6 (w1).

You can find Goal Seek in Excel 2010 under Data, What-If Analysis.

In cell E12, we calculate r = R^(1/5) and Re (cell F12) from our formula for Ro.

The results are above and are very close to the actual case numbers on 21 March and 26 March.

In the image below we look at Omicron where we may expect (potentially) case numbers to triple over a two day period. This means r = SQRT(3).

We set cell E9 to the total case numbers on 26 March (2,430).

This time we set R to cell E30/10 and use Goal Seek in Excel as above.

i.e. We use Goal Seek to set E10 to 0 by changing cell E6 (w1).

We calculate r = R^(1/5) and Re from our formula for Ro.

Once again the numbers are very close to what we want.

For background see:

COVID Odyssey: NZ New Year Fear 24 Post #951~ COVID-19 NZ: COVID-19 spread using two cycles and Goal Seek  

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