April 15, 2020

Case numbers slowing, but keeping the gains critical

Have “We got this” yet?

The colloquial phrase that Anika Moa, Taika Waititi and others have invoked as the ‘kia kaha’ of this pandemic is “We got this!”. Here we look at the track of new and recovered cases of the virus to see whether the New Zealand community is likely to be able to make that claim by 20 April.

The total cases are reaching a plateau of around 1,400 people


Source: Ministry of Health

Three weeks ago, the track of the numbers of recorded confirmed and probable cases of COVID-19 began increasing rapidly by over 40 per day. The track peaked in the 70’s and 80’s a day. Seven days ago the daily increase began dropping and tracked down to 17 by 14 April and is still low at 20 today, 15 April.

There are ups and downs as different cluster investigations and repatriations into the country affect some daily numbers, but the general direction of daily cases continues downwards as the reported cases reach a plateau.

At 15 April there are more people recovered than still have the virus

The other important track is how many people have recovered from the virus, and how quickly. One week ago the number of people reported as recovered from the virus increased above 30 a day and has generally tracked upwards from there since. On 13 April the number was 75 recovered cases, on 14 April, 82 cases, and on 15 April is 100. These are a similar level to the number of the new cases 15 to 16 days earlier.  

The cases are counted as recovered when it is at least 10 days since they were first recorded and they have been symptom free for 48 hours. (Unfortunately recovery date individually for each case is not yet shown on the records.)

So if we take the total recorded confirmed and probable cases and subtract the recovered cases we have a measure of the number of cases not yet symptom free for 48 hours. These have been called ‘active’ cases. The chart shows that active cases peaked at about 950 cases on 5 April. They have since dropped to about 650 cases.

The number of people recovered by 15 April are 727 which is more than the 650 people still with active virus.

Projecting the shapes of these curves to 20 April

The total of all confirmed and probable cases appears to be reaching a plateau at a little above 1,400 cases.  

Source: Ministry of Health and BERL calculations

This is not a forecast, but a visual extension of the shape of the curves for the recorded cases and the recovered cases. This would indicate that by 20 April, the number of active cases may have reduced from about 950 to as low as about 250 or 300.
Achieving an ongoing rate of no new cases is not a given. When we move to Alert Level 3, strong discipline will still be necessary at the border, and testing of essential workers and their contacts. It will be important also to ensure that any possible cases of COVID-19 relapse are found and the surrounding infections squashed.

Are the aged at an increased risk?

It has always been known that the aged and the medically compromised are at increased risk of bad outcomes from the virus. It is important to see if, to date, the aged have suffered a rate of infection that is greater and increasing compared with other age groups.

The number of confirmed and probable cases for the adult age groups of 20 to 39 years, 40 to 59 years and for 60 years to 70+ years have been plotted until 12 April. (The 0 years to 19 years have had a low incidence.)

Source: Ministry of Health

The shape of the curves indicate that the number of those in the 20 to 39 years age group became the dominant group early, has maintained that position, and is only flattening the curve recently.  The number of those aged 40 to 59 years is about three quarters that of the younger age group, and is flattening now also.

Encouragingly the oldest age group of 60 to 70+ years began to flatten at about 5 April. It is under half the number in the 20 to 39 age group. Interesting also to note that the aged care-related cases in Christchurch appear to be those on 3 and 4 April causing the slight uplift in this curve then.

From 5 to 12 April there were 22 additional cases in this age group, an increase by three persons per day. There is no evidence that the virus infections are expanding greatly in the older age groups, although sadly, the deaths from COVID-19 are all in this group.

20 April decision critically rests on keeping the gains

  • A range of Treasury economic scenarios which depend a lot on the length of time we are at Alert Levels 4 and 3.
  • The COVID situation is expected to see the total cases to be near or at a plateau, and there could even have been a day with no new cases.
  • The number of people with active viruses could be at about 250 to 300, and as at present, not a high percentage hospitalised.
  • As experts have been warning, saddening as it is, we must be ready for more deaths. But the age-profile of cases in the last week is promising in that the number should remain small.

In terms of the virus, by 20 April the New Zealand community could well claim “We got this!”. The challenge then is “How do we keep this?”. And how to keep these gains will be critical in the decision to be made on 20 April.