This paper summarises the modelling advice provided to Cabinet during the August 2020 outbreak of Covid-19 in Auckland, as well as detailing the methods used to provide that advice. The actual values provided, particularly the probability of elimination and the effective reproduction value, vary depending on the date the advice was given. Values given here are representative of those calculated in the later part of the outbreak (October 2020).
Executive summary
- For the Auckland August outbreak, the effective reproduction number Reff was found to be between 2.1 and 2.5 before Auckland moved to Alert Level 3 on August 12 2020 and between 0.6 and 0.8 during Alert Level 3.
- This was a higher value for R<subeff in August pre-lockdown compared to that seen pre-lockdown in the March/April outbreak. This may be due to a combination of factors, including Alert Level 1 conditions (no gathering size restrictions, etc.), different behaviour of cases associated with international travel in March/April, higher transmission rates in winter, and differences between the communities affected.
- Highly effective contact tracing and case isolation played an important role in keeping R<subeff below 1 in Alert Level 3 and 2.5/2.
- We estimated that it was highly likely that the Auckland August cluster was eliminated by 5 October before Auckland returned to Alert Level 1 on 7 October. However, in scenarios that did not lead to elimination, case numbers grew rapidly in the absence of Alert Level 3 restrictions.