Time now to focus on virus loopholes
Epidemiologist
The key to success in quickly eliminating Covid-19 from New Zealand is to make the right decisions at the right time. That means focusing on the facts, and asking the right questions.
So far, the strategy being applied in New Zealand appears to be working far better than the policies adopted in most other countries. Both the nature of the controls and the timing of their implementation have been very effective.
Although the total count of cases keeps increasing, it is not a useful guide to what actions are now needed. The key piece of information is the trend in the number of confirmed new infections per day. That is now going down at a very promising rate, taking into account that it is measuring the policy five to 10 days earlier, which is when today’s new cases became infected.
So the situation should continue to improve faster over the next two weeks. However, it would be very foolish for the lockdown to be ended before 28 days.
Over the second two weeks we will learn who got infected since the lockdown, and whether there are any loopholes in what has been done, which could cause a surge of cases once restrictions are eased. If the public attitude is allowed to relax too early, the disease will bounce back.
Jacinda Ardern has done a great job of keeping the whole country working together to eliminate the disease without the high and lengthy human cost being suffered by other countries.
We need to focus all the effort on identifying possible loopholes that need to be dealt with. What are they?
We need to understand whether the ‘‘probables’’ are really Covid-19 and, if so, why these people are testing negative. The global case counts are only of laboratoryconfirmed cases, as required by World Health Organisation. Our count also includes probables.
In New Zealand the number of confirmed cases is going down, but the proportion of probables in the total is going up, as shown in the accompanying ESR graphic. If most of the probables are not true Covid-19 cases, then control is working very well.
However, if the test is in fact missing a substantial proportion of cases, then that means there are a lot more infected people around the country than we are estimating from the test results. So far there are no clear indications that the test is failing to detect so many true cases, and therefore perhaps most of them are due to clinicians classifying too many people as cases, when they have other causes for their disease.
The second issue is the continuing high number of infections with unknown source – currently 14 per cent, as against 2 per cent classified as community transmission. These percentages have changed very little over the last two weeks, yet we urgently need to know the true level of community transmission.
If the source remains unknown after careful investigation, we have to conclude it is most likely to be community transmission, which is therefore about 16 per cent of the total, and about a quarter of all infections acquired within New Zealand. That is worryingly high, and we need to understand these cases far better – where are they around the country, are there things they tell us about loopholes in the control, and so on.
Almost 60 per cent of the domestically acquired infections are in 12 known clusters of up to 84 people. Surprisingly, that is good news. Clusters are much easier to investigate and manage than single unexplained cases dotted around the country.
The other 40 per cent are the ones that could undermine controls when the lockdown is relaxed, so we need to understand where they are and more about them in order to close any loopholes in the current strategy.
So far, the signs are very promising that we can eliminate Covid-19 from New Zealand more rapidly than in any other country. However, we need to urgently use all the available epidemiological tools to dig deeper into finding any loopholes and fixing them.
Professor Roger Morris has been involved in around 30 disease control and elimination programmes throughout the world, involving both animals and people. He is currently advising the World Bank on part of its planned investment of up to US$160 billion to assist countries to recover from Covid-19, and to prevent a future pandemic.