COVID Odyssey: Worldwide Winter Windup 9 ~ Ro > Re ~ How much greater is Ro?

We consider how much greater Ro  is than Re.

We look at the following table:


For definitions see:


In New Zealand  both r = SQRT(2) and r = 1.429 provide good estimates for the total number of cases from 21 to 25 August 2021. See:

COVID Odyssey: Winter Warning NZ 15 ~ Delta variant outbreak 2021 ~ Estimating Ro and Re

These values for r correspond to Re = 6.047 and Re = 6.308.

This gives us the above range in New Zealand for the delta variant under Lockdown Level 4.

We obtain Ro in New Zealand in the 2021 Lockdown level 4 could have been as high as 6.57.

In New Zealand we have seen r =1.4 works well for a daily growth factor.

1.4 x 1.4 = 1.96.

This means that cans that we can expect case numbers to almost potentially double every two days.

Case numbers could double every two days if r = SQRT(2).

We use this value to estimate Ro using our formula:


We use the factor F = SQRT(2)/1.4 to estimate Ro for other values of Re.

This provides us with the estimates in the table at the top of this post.

We have also seen in China and the USA in early 2020 r is close to 1.5.

This provides us with Ro = 7.931.

This gives us a range for Ro for the original COVID-19 outbreak in 2020 of 5 to 8.

Recall that for UK in early 2020 we estimate r > 1.35 and  hence Ro is at least 5. See:

COVID Odyssey: Worldwide Winter Windup 5 ~ Revised estimates for Re worldwide

COVID Odyssey: Worldwide Winter Windup 6 ~ Ro ~ Estimates for the Alpha and Delta variants

We obtain the table below:


The PDF version may be easier to read:


Ro may be far greater than Re than we have indicated.

The factor and values of r we have used to calculate Ro provide a minimal estimate just over 1% higher than high values of r we have used to estimate Re.

The effect of the increase can be seen here:

COVID Odyssey: Winter Warning NZ 10 ~ Delta variant ~ Analysis

Higher factors may increase the range significantly for our estimates for Ro.

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