Covid-19 attack rates, herd immunity, and why SA is far from the end

As we rapidly approach the peak of infections in South Africa, there are officially 381,798 positive Covid-19 cases, with 208,144 recoveries and 5,368 deaths. SA’s number of Covid-19 cases per 100,000 people is growing at a higher rate than any other country in the world. However, as the global death toll continues to rise, our mortality rate remains one of the lowest. Ron Whelan explains why SA’s numbers are so high, and what it will take before we see an improvement. – Claire Badenhorst

South Africa and Covid: A grim reality 

Dr Ron Whelan is the chief commercial officer at Discovery Health. As we go into another week of this Covid pandemic, it seems as though the situation in provinces outside of the Western Cape is now accelerating and getting a lot more difficult. What feedback are you seeing?

It’s certainly interesting times. South Africa’s trajectory continues to remain serious and concerning. Globally, we now have the fifth-highest total number of infections, which is a concern. The only countries ahead of us are the US, Brazil, Russia, and India. In addition, our attack rate remains one of the highest levels.

The attack rate as of this weekend is 22 new infections per 100,000 population. As I’ve mentioned previously on the show, Europe peaked at 10 new infections per 100,000 per day, so we’ve doubled the attack rate at which Europe peaked. Our attack rate is also higher than Chile and Brazil at the moment; it’s around about the same as the US. On a South Africa basis, unfortunately, things are not looking good.

It’s not all bad news, though

What is looking promising, however, is that the Western Cape is still on a downward trajectory. As of this weekend, the Western Cape’s attack rate is 15.8 per 100,000 population per day. You’ll remember that the Western Cape peaked at about 24, so it’s down and it’s maintained this trajectory now for the last six weeks. That’s really, really promising. In fact, on a compound daily growth rate, the Western Cape is tracking at about 1%, which is very good.

What we’ve also seen and it’s very, very early signs, is the last three or four days have looked a lot more stable in Gauteng and in the Eastern Cape. In the last four days, Gauteng has been tracking on about 5,000 new infections per day. That’s a big number but the good news around that number is it doesn’t seem to be growing. We’re watching those numbers very closely at the moment and we’re certainly hoping that Gauteng starts to taper off. We’re seeing a similar number play out in the Eastern Cape as well; North West to a greater or lesser degree. On the other side, the Free State and KZN are tracking upwards. It just seems to be the trend across South Africa. It’s been the Western Cape, then the Eastern Cape and Gauteng, and now the next two provinces in the mix.

That’s quite good news, given that the Eastern Cape and Gauteng are highly populous areas. If they have already started to plateau, is this aligned with what happened in the Western Cape? Maybe just unpack that for us as well— what the attack rate means. Are the attack rates in those two provinces still growing?

The attack rates have flattened, admittedly, at a much higher level than where the Western Cape did. As I mentioned before, the Western Cape flattened at an attack rate of 23.9 new infections per 100,000 per day. Gauteng is up to 33 new infections per 100,000 per day. It’s about 50% higher than where the Western Cape was at but what we really look for is for these rates to start flattening at some point and then ideally to start declining. That means that you’re starting to see proportionately less new infections on a daily basis and it’s not eating into the population as much as it would have been previously.

The Eastern Cape is at 27. These numbers are very, very high; let’s be honest about that, but they’ve got to come off at some point and at least they don’t seem to be rising. We will have a much better indication over the next three or four days or so, but fingers crossed, we’re headed in the right direction.

A unique situation in South Africa

Why are they so high? When we first heard of what was going on in Europe, it was frightening. Yet, from what you’re telling us now, the infection growth in South Africa is even higher.

The reality is that we’re working in a different environment in South Africa. Often this happens in the highly densely-populated areas and the virus obviously spreads from one person to the next. We are very dense in many areas in South Africa.

Secondly, remember, Europe’s attack rates were recorded in a lockdown environment. When Europe was starting out it was largely lockdown across Europe. You’ll remember South Africa’s infection rates when we were in lockdown were extremely low, as low as South Korea at the time. Our attack rates are in a very different environment to what Europe was in when they were recording their attack rates.

What is interesting about our attack rates is that they’re almost identical on a national basis to the US at the moment. The US is also tracking at around 22 new infections per 100,000 per day. You can see that the US economy is largely open again; people are going about their business. We’re seeing quite similar trends across the US.

What is herd immunity and can it help to stop Covid?

That’s still relative to the 100,000 people that it’s a percentage of. Very small. What happens here? You’re a medical doctor— does everybody get sick? Is that when the virus ends, or do only some of us get sick?

I think you’re pointing to this point around herd immunity and there’s lots of debate happening around herd immunity at the moment. The principal around herd immunity is that the virus has relatively less opportunity to attack, to pass on. Obviously, if more people have already had the virus and they’re immune to the virus, then the virus has less opportunity to be passed on. That’s called the susceptible population. In actuarial models, they will speak about the susceptible population. A susceptible population is a population that the virus can then go ahead and attack and if people have got antibodies through immunity over a period of time, it eventually fizzles out. Herd immunity happens when somewhere between 60% and 70% of the population has been infected at some point in time. That’s where you start getting a less proportionately susceptible population and the virus slowly starts to fizzle out.

We are a long way from there?

We’re a long way from there, yet. When one considers our registered infections at the moment are in the upper 300,000 or so— 300,000 out of a population of 60 million is quite a long way to go to 60% or 70%. Admittedly, the infections we’ve got at the moment are not a true representation of everyone who has had the virus in South Africa. In fact, when you look at the US and Brazil, their estimation is that their actual infection counts or the actual prevalence is 10 times higher than what’s been reported. Brazil, for example, would have two million infections at the moment; the estimates are that closer to 20 million people in Brazil would have been infected.

If you extrapolate that across South Africa, we would be talking about 10 times our current numbers— somewhere between three and a half, and four million people who have been infected. Even at that level, we’re 5% of our population that’s been infected. Calibrate that back to the number I mentioned previously; 60% of the population needs to be infected for herd immunity. On a population of 60 million people, that’s 36 million people. We’re still a long way from herd immunity and this is why the vaccine development is so important.

Fortunately, we’re starting to see some good news about vaccine development, both globally as well as in South Africa. Looks like we’re going to be moving into phase three trials of the Oxford vaccine. The Moderna vaccine is just starting to show promising progress. Still a long way off— anywhere between six months and 12 months towards a vaccine, but that’s what we’ve got to be working on.

A low fatality rate, thanks to age and medicine

The mortality rate in South Africa— the official mortality rate, anyway— is very low compared with other parts of the world. Do you have any insight into why this is so?

I’m delighted that the mortality rates are still so low in South Africa. The mortality rate in South Africa— the latest number is 1.4%— or the ‘case fatality rate’. The case fatality rate is the number of deaths divided by the number of infections. We’re at 1.4%, which is somewhere around about a third of the global averages. The global case fatality rate is somewhere between 5% and 6%, so at 1.4% we are lower than a third— about a quarter of global case fatality rates.

I think there are three main reasons for that. The first reason is South Africa’s population is relatively youthful compared to Europe’s. So, an average age of 28 versus an average age of somewhere between 40 and 45 in Europe.

The second reason is that when the infection spread through Europe and most parts of New York, what we found was a pattern where it was really severe in nursing homes and elderly homes. We know that Covid is particularly aggressive in elderly populations. In the elderly populations across our Discovery database, we see a case fatality rate of about 13% in people over the age of 80. So, over the age of 80, it’s really, really aggressive. Between the ages of 60 and 70, we’ve seen a case fatality rate of somewhere between 3% and 4%. So, it’s very skewed toward the elderly. When you look at what happened globally, Covid attacked nursing homes and retirement villages across Italy, New York, and the UK in particular. That pushed up the case fatality rate there.

The third reason— and I think this is an exciting reason— the case fatality rate is lower in South Africa because our physicians have been remarkable. They’ve been up to speed with the latest treatments for Covid. We were quickly on to dexamethasone therapy, we were quickly onto high flow nasal oxygen therapy, we were quickly into the prone position. Our physicians across South Africa have done a remarkable job of being way ahead of the curve in terms of treatment modalities. We’re seeing that playing out across our Discovery statistics as well. In fact, we’re starting to see some patterns where the Gauteng case fatality rates are lower than the Western Cape. I think this points to quickly adopting new technologies and new treatments.