COVID Odyssey: NZ New Year Fear 8 Post #935~ NZ Omicron: Estimating Ro

We use actual case numbers for the Omicron variant in New Zealand to estimate Ro.

We find that case numbers may potentially triple in a two-day period.

For update see:

To estimate Ro (the average number of people one person may infect without isolation over a 10-day infectious period), we need to estimate (project) the number of people a case may infect if the case had not been isolated.

For background see:

Step 1

We look at the daily increase (r). We use this to project additional cases.

Below are actual case numbers (first two columns):


Note that on 26 January there are 12 historic cases that have not been included as cases for the day (they are in the total).

“In addition, there is a total of 12 cases linked to the three border workers reported earlier this month with confirmed or suspected Omicron, an increase of six.” See:

On 28 January we had only 15 new cases. The curve appears to be starting to flatten at least until we have some super-spreader events.

Step 2


We have found that a weighted average works better to estimate r.

We see that r is close to SQRT(3).

This means that case numbers could triple over a two-day period.

Compare the second Total column with the last column.

Step 3

We use the weighted average column for the factor.


Step 4

We use 0.732 as the Factor.


We see on 27 January the totals are close.

We look at this table:



We see that for r = 1.732, Ro ~ 12.73.

We also see that for r = 1.66 (Step 2 and Step 3), Ro ~ 11.

1.73 – 1.66 = 0.07

1.73 + 0.07 = 1.8

For r = 1.8, Ro ~ 14.4

These estimates (Ro from 11 to 14.4) are within our previously estimated range for Omicron. See:

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