The key issue with eliminating COVID-19 from New Zealand is whether or not the transmission rate, alternatively worded as the reproduction rate, R., can be reduced to well below ‘1’ and kept there. This value of R=1 is where each infected person on average infects one other person.
If this rate can be held below ‘1’ then the disease will eventually die out by itself from within the community. The further the R value is below ‘1’, then the faster the disease will fade away.
The current expectation is that daily rates of new cases will increase through to about 6 April. No-one knows what that peak rate will be. The fact that it has declined a little from 83 on 28 March to 63 on 29 March is certainly good news but it may also mean absolutely nothing.
Taking Spain as an example, since their lockdown on 14 March, which appears to have been strictly observed, new case rates have declined on four different days, but the overall trend of new daily cases has been strongly upwards, having risen from 1159 on 14 March at the start of lockdown to 7516 on 28 March. They may now have just turned the corner, but it will be another two to three days before we can be sure. Spain is worth watching, because their lockdown has been strict, somewhat like ours.
Regardless of where we peak, we should know well before the four-week lockdown period is over whether or not we are on track. If we reach our peak daily cases by around 6 April, as seems reasonable and as the Prime Minister is suggesting, and if our lockdown is strict enough to get an R value of 0.5, then daily cases should decline thereafter by between 60% and 75% over the following two weeks. And from there we should be able to quickly drive it down close to zero.
However, if we can only get the R value down to around 0.75, then it is going to take much longer. Modelling published here and supplied to Government assumed R=0.75 as their lowest tested result, and they thought that it would take too long at this level for the program to be sustainable. So, we really do have to go hard over the next few weeks to get on top of things.
The likely reason we have seen daily case rates stabilising on 28 March at 83 (from 85 the previous day) and then declining on 29 March to 63 new cases is that we are seeing fewer primary cases from new arrivals into New Zealand. The big question relates to the unseen waves in the pipeline from existing cases, with these having been seeded already from existing cases. The answer will become evident over the next one to two weeks.
One of the real problems that can negate achievement of a low R value is super-spreader events where one person directly or indirectly affects many others. Currently in New Zealand we have at seven clusters which have acted as super-efficient spreaders. These is the Marist College in Auckland, the World Hereford Conference in Queenstown, a private wedding in Wellington, a US travel group from Wellington, a Hamilton Rest Home, a publicly undefined group from Matamata, and a Christchurch workplace. Each cluster has between nine and 36 cases, adding to 113 cases across all clusters, with numbers still climbing. If we are to get the overall average transmission rate below ‘1’ hereafter, then any new clusters have to be balanced elsewhere by many cases that infect no-one.
So, there is a simple message there: do everything possible to avoid cluster events. And let’s hope we have no big super-spreading events in the pipeline.
Big cluster events overseas have included church events in Korea and Singapore, large private dinners in Singapore and elsewhere, weddings in multiple countries, a football game in Northern Italy between Valencia and the local Atalanta team, which in all likelihood was the super-spreader event transferring the disease to Spain, and beer-pong in a well-known Austrian pub in the resort of Ischgl. This last event apparently led to transfer cross much of Northern Europe.
For those who don’t know the game of beer-pong, it is a well-known drinking game played by a different generation to me, that has a number of variants. Most of those variants were identified a long time ago as a source of ‘pong-flu’ linked to poor drinking hygiene. It seems the Austrian version played in Ischgl had particularly poor hygiene, with participants using shared whistles to project the pong balls into cups of beer which other people then had to drink. Yuck!
Where things can really turn to custard is when one super-spreader seeds another super-spreader. That is the risk we face right now in New Zealand, particularly from the Hereford Conference. That cluster only become apparent when an Australian left the conference early to return home in an attempt to beat the Australian isolation edict. Fortunately, she was quickly tested on showing symptoms back in Australia.
In contrast, Hereford Conference attendees here in NZ who became sick were refused testing because they had not travelled overseas. Further, authorities downplayed the risk arising from the Australian attendee because that person left the conference before being likely to be infective. Alas, the question was not asked as to where that person might have got the virus!
The Hereford Conference saga, as told to me by participants, is in fact somewhat longer than this but I will leave it there. Each of the super-spreader events will have its own story as to how it happened and how it could have been minimised.
There are some interesting demographics relating to the people who have currently been infected. I have drawn this information directly from the Ministry of Health spreadsheets available at their website.
Females comprise 54% and males 46%. We cannot read much into that at all, except that it does seem to contradict earlier suggestions that case rates were higher in males.
More intriguing is the age groups of the cases, with the 20-29 age group being easily the largest and comprising 24% of the total. In contrast, the over-70 cohort comprises only seven percent of total cases. It is also notable that in the big 20-29 age group, 62% are women. That raises interesting questions as to the social behaviours of this group.
Maori infection rates are only four percent of the total and Pacific Island rates a little over two percent. This probably says nothing more than that these groups travel less to Europe and the Americas than other demographic groups. It says nothing about their susceptibility to infection if the virus really takes hold within New Zealand.
People of Asian ethnicity are also under-represented in the COVID-19 statistics at seven percent, with European ethnicities being the ones that are over-represented. All of this probably says more about who has been travelling to overseas hotspots rather than any underlying susceptibilities.
Each day I search for evidence from overseas as to which countries have clearly reached peak daily cases and are now in major decline. Basically, there are none except for China, which now has very few new cases and with most of those few cases coming from people returning to China. China is not yet back to normal but it is close, with factories and restaurants largely open, and schools now starting to open in some provinces.
A likely explanation why we are not seeing a decline in other countries is that most of the lockdowns, where they are in place at all, have been in place for less than 14 days. The next few days should start to tell a story.
If we and other countries fail to get a quick turnaround then we will have to ask ourselves what are the weak links in our approach.
Almost certainly, the biggest weakness in our existing program is insufficient testing. Until we can test everybody who has symptoms, regardless of other factors, then we have no way of knowing the extent of community transmission.
The Ministry of Health, driven most likely by the need to maintain community support, which in Government jargon is known as ‘maintaining social licence’, has largely been in denial on that matter. Beneath the waters, they will be paddling furiously to further increase our testing capacity, but they do need to ‘fess-up’ that it is an issue.
It is the absence of sufficient testing that reinforces the reality that we all have to act with social distancing and lockdowns as if we have already been infected. It also means that as a nation we have one hand tied behind our backs.
On a global basis, it is obvious that we are in the middle of Wave 2. Wave 1 was China and it peaked in mid-February. Wave 2 is centred in Europe and the Americas and has yet to peak. It will take a lot longer to fade away than Wave 1. Wave 3 will be across the rest of the world. As of yet, Wave 3 is only just starting, but the trajectory is already there and it looks sure to happen. It is likely to be the biggest wave.
Once we can get on top of our own New Zealand epidemic, we will have to work out where we go from there in a world that is still full of COVID-19. The first step will be to work out how to relax the pressure internally, so that social licence is maintained but the disease does not run away from us again.
I think a lot of people will have ideas as to how that could and should happen. Anything that might create a super-spreading event cannot be allowed. That means ongoing restrictions on social events of any scale. Also, border restrictions will have to be very tight and with entry totally controlled.
Keith Woodford was Professor of Farm Management and Agribusiness at Lincoln University for 15 years through to 2015. He is now Principal Consultant at AgriFood Systems Ltd, and has had a longstanding interest in epidemiology. He can be contacted at firstname.lastname@example.org Previous articles can be found at https://keithwoodford.wordpress.com