COVID Odyssey: Winter Windup 9 ~ COVID- 19 Delta Variant 2021 ~ Is Ro in the range 9 to 12.7?

The Delta variant of COVID-19 appears to be twice as infectious as the original 2020 outbreak. for the 2020 outbreak we estimated Ro = 6. In previous posts we simulated outbreaks using a value for Ro around 12.7 (actually Ro = SQRT(3)).

In this post we consider also Ro = 9 (halfway between 6 and 12) to get a range for Ro for the Delta variant from 9 to 12.7.

Please look at the last column of the table below. The last column  has values of Ro for an infectious period of n = 10 days.


For the initial outbreak we calculated from the table Ro = 6 for a daily rate of increase in infections of r = SQRT(2).

For the Delta variant in previous posts we calculated Ro = 12.7 corresponding in the table for a daily rate of increase of r = SQRT(3).

In this post we see Ro = 9 corresponds to a daily rate of r = 1.57 to get a range for Ro for the Delta variant between 9 and 12.7.

It is probably easier to start at n = 7 for r = SQRT(3) to get a similar range 9 to 12.7.

Remember that a person may be infectious days before being symptomatic (showing symptoms).

Assuming that contact tracing, quarantining and isolation of cases may halve the effective number of infectious days, we look at the first column in the table (n = 5) to get a value for Re (the effective Reproduction number).

Corresponding to r = 1.57 we get Re = 5.

For the upper value in the range, we look at n = 6 days (one day later).

Now look at n = 6 in the table. For r = SQRT(3) in the last row, the table gives Re = 7.9.

This gives a range estimate for Re of 5 to 7.9, similar to the values for Ro for the Delta variant estimated in the range 5 to 8 below:


i.e. One person may effectively infect 5 to 8 other people. Re in our analysis may be in the range 5 to 8.

For more information see:

Search Results for “windup” – COVID Odyssey by Alan Grace: My vir[tu]al COVID-19 journey (

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COVID Odyssey: Winter Windup 6 ~ COVID-19 Delta Variant 2021 ~ Does Ro = 12?

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