In this post we conclude that we need to go back to our original results for estimating Ro.
By definition we let:
- r denote the effective Reproduction rate of COVID-19 for one day
- Ro (R0; R-Zero; R-Nought) denote the Reproduction number for COVID-19 without any quarantine or isolation
- Re denote the effective Reproduction number for COVID-19
(Re assumes isolation/quarantine is happening)
- a case be defined as a person diagnosed as having COVID-19
Note that Ro and Re are numbers (not rates), the number of people one person with COVID-19 may infect on average without quarantine or isolation (Ro) and with quarantine or isolation (Re).
We have always found that a daily increase of r = 1.4 for estimating COVID-19 cases in New Zealand works well up until the day after Lockdown Level 4 started at 11.59 pm on 25 March 2020:
We also realised that our original calculations for Ro were best:
We used simulations to estimate/verify Ro and our subsequent Ro formula at the top of the previous table. Sample results from simulations for n = 10 days are below for r = 1.4 and r = SQRT(2):
We conclude that Re = 5.8 and Ro = 6 in New Zealand in early 2020.
This means that on average one person may infect 6 other people over a 10-day period.
Note: to convert to/from our original results multiply or divide by r.
Any estimates for Ro around 4 in previous posts should be multiplied by r.
Since 1.4*1.4 = 1.96 and SQRT(2)*SQRT(2) = 2, the number of cases could double every 2 days.
For more information see: