COVID-19 NZ: Can one person infect 2.6 others?

We investigate to see if in New Zealand one person may infect 2.6 others.

We consider again this image:


Source: New York Times.

How can a Coronavirus out-spread from 5 to 368 people in 5 Cycles (Credit: The New York Times)?

If 5 people with new coronavirus can impact 2.6 others each, then 5 people could be sick after 1 Cycle, 18 people after 2 Cycles, 52 people after 3 Cycles and so on. See:

See highlighted column below:


The above has a 6-day cycle.

For New Zealand we choose a 5-day cycle.


We calculate Re = 2.665932044 to match the number of new cases on 29 March.

We conclude that instead of calling this Re, it is better to call this Ro (R-zero).

Ro is used for the rate without quarantine whereas Re is used when there is quarantine.

New Zealand went into Lockdown Level 4 on 25 March at 11.59 pm.

This meant that new cases on 29 March were infected before Lockdown.

We also note the highlighted figures in the last column (the actual number of new cases) are no longer exponential and appear linear with a gradient slightly less than 1.

Note that the actual number of new cases is actually the increase from 5 days before (previous cycle).

We graph the results below:


Below is the bar graph for the actual daily new cases:


We also note that the ratio of the estimated Total Infected also reaches the Re (or Ro) value.


We conclude that in New Zealand one person can infect at least 2.666 other people (on average) up to near the end of March.

We adopt

Ro = 2.666 (about 2 and 2/3 )

In the above model it is assumed that only new cases can infect others (after an incubation period of one cycle).

If the infectious period is two cycles then we would need to add 1 onto the Ro value. i.e.

Ro = 3.666

This means that one person could infect at least 3.6 other people.


If instead it is desirable to match the total number of cases, see below:


Note that Ro is still over 2.6 (2.612).

My other COVID-19 posts can be found here:

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