What comes next in NZ’s grand plan
Will we see many more cases of Covid-19? Can we eliminate the disease from New Zealand? The world? So far, New Zealand has done exceptionally well in reducing the transmission rate to well below one new infection from each infected person. Some countries have at worst been approaching five, meaning the disease spreads like wildfire.
As we move to alert level 3, the number of cases reported each day is getting close to zero, but contact among people will now increase. It would be remarkable if we saw no more clusters of infection arise. What is likely is that we will get a blip of new cases starting in the second week of level 3, from May 5.
Although the testing programme has been very extensive, relative to the size of the outbreak, it cannot detect every case. With an incubation period of five to 10 days, contacts of the undetected infected people will start to show up with the disease from May 5.
Finding new cases would be helpful, by flushing out hidden clusters of infection. With a ‘‘zero tolerance’’ policy, in which prompt action is taken to isolate infected people and rapidly trace contacts, we should get the true level of infection to zero within perhaps three months, with a very low risk of resurgence.
It will take longer to provide confidence that the infection has been eliminated, and we may still have an occasional case for some time, perhaps arising from an infected traveller who is still excreting virus after completing quarantine. The virus seems to remain active longer in a few people.
Australia has had a softer lockdown policy than New Zealand, and hence there may be more hidden clusters of infection in the community there, since they will not have lowered the transmission rate as far as New Zealand. Unless Australia has been extremely lucky, it is likely to have cases continuing for longer than New Zealand, and may have greater difficulty reaching elimination.
New Zealand is likely to gain economic benefits from rapid elimination of the virus, and hence speedier return to normal business activities.
Each time a new disease enters the human population, we watch carefully for any ‘‘sting in the tail’’ of infection, where the virus has effects that take time to detect. Loss of smell and taste in infected people has already been reported widely in this pandemic.
There is now growing evidence that coronavirus also affects blood clotting in the body. This seems to influence the difference in severity of disease between people, and is now also being identified as the likely cause of serious strokes in unusually young people who have become infected but have not necessarily had severe pneumonia.
The virus affects multiple organs other than the lungs, so there may be further stings yet to show up. New Zealanders have therefore gained from keeping the number of cases very low.
If New Zealand eliminates the virus, it will be the first country to achieve freedom. But can we eliminate it from the entire human population, as happened with the Sars coronavirus? That virus still occurs in bats in China, but no longer in people anywhere in the world.
China, despite having the largest population of any country, has succeeded through intensive lockdown in getting surprisingly quickly to the point where almost all of its 10 to 20 reported cases of Covid-19 each day are in arriving travellers. So elimination of the disease in large populations is possible.
The problem lies in countries where control is haphazard, which provides gaps for the virus to maintain itself. ‘‘Herd immunity’’ by natural spread will never eliminate global infection with this particular virus. A highly protective vaccine would almost certainly make global control possible. However, it is far from certain that such a vaccine can be developed and, if it can, it will take a long while to be distributed widely enough to stop the disease globally.
Meanwhile, New Zealand will provide a valuable lesson in the effects of a carefully implemented control and elimination policy. If we succeed, so can other countries.