Escaping Covid confusion

COMMENT

President Cyril Ramaphosa’s address to the nation on August 15 announcing the transition to alert level 2 contained one really important point that cannot be overemphasised: we must not get complacent and relax containment measures.

Predictably, opposition politicians have attacked the government for causing too much economic damage. Have they not been watching the news from around the world? Whereas we can argue about missteps and the detail, the government has managed this far better than many supposedly advanced nations. The United States and United Kingdom have had quarterly GDP drops and rises of unemployment on the same scale or worse than the 1929 crash.

I argue elsewhere that the big economic risk is how we manage post-pandemic recovery. Managing the pandemic required quick decision-making under uncertainty so mis-steps shouldn’t be surprising. As World Health Organisation (WHO) expert Michael Ryan eloquently informed us at the start: “Perfection is the enemy of the good … speed trumps perfection.”

The most important thing we need to understand about where we are now and what to do next is that there are still many unknowns.

When you talk to your doctor, the last thing you want to hear is: “I don’t know.” But in the current situation, that is often the most accurate answer. In any complex, real-world situation, the best scientific advice has to include a significant aspect of uncertainty. The people to distrust the most are those who claim certainty.


What I aim to do here is to make it clearer what is uncertain and why that is not cause for concern — as long as we continue to react to the evidence and adjust our approach as new facts come in.

Mask effects

An example of how not to do it is the approach to mass wearing of masks in the US and UK. In March, a small group here in Makhanda started reviewing the evidence for masks for all. We noted the rapid adoption of informal face covering in the Czech Republic as well as the widespread use of masks in and near China. The WHO advice at the time was not to wear a mask unless you were dealing with infected cases or were infected yourself. The big problem with this advice was the growing evidence that a high fraction of cases is asymptomatic and that contagiousness peaks two to three days before symptoms show. So the WHO advice, read with this new information, suggested that everyone should wear masks in public because we do not know who is infectious.

Why did the WHO and many health authorities take so long to alter their advice? Two reasons: there was a concern that the public would buy medical-grade masks in large numbers when there was an undersupply for medical personnel and a factor that leading climate scientist James Hansen calls “scientific reticence”. The first problem is quickly dismissed by encouraging the use of homemade masks; the second is a bigger problem that needs more thought.

Scientific reticence arises from two issues: scientists don’t like to be accused of alarmism and anti-science argument forces scientists on to the defensive. Add to that the fact that the anti-science argument is often asserted with absurd certainty and the uninformed observer is led to believe that the scientists are the ones who don’t know what they are talking about. A consequence of scientific reticence is that scientists are often reluctant to promote something against a background of controversy without very solid evidence.

For mask wearing, the evidence was strong but not solid at the early stages of the pandemic. No one has studied containment of this specific virus using informal cloth masks and pre-symptomatic and asymptomatic contagion had not been studied in detail. Nonetheless, based on Ryan’s advice to move fast rather than await certainty, early adoption of universal public masking was the right decision.

How is South Africa doing?

At this checkpoint of the move to level 2: how is South Africa doing? Official statistics show active cases peaking on July 20 and 11 839 deaths out of 587 345 cases, a case fatality rate of 2%. This contrasts with the 3% case fatality rate of the US and 13% in the UK. If, however, we look at excess mortality (deaths over and above the average for that time of year), the latest report covering May 6 – August 4 records 33 478 excess deaths; over this period, the official Covid-19 death toll was 8 884, suggesting that the true toll could be nearly four times the official number. 

That is not a correction, however, that we can apply in a straightforward way to the case fatality rate. Test positivity (the fraction of those who are tested who test positive) has been over 10% for a long time and approached 30% at its peak. That means the true number infected is likely to be many times the number of cases (a case, by definition, is confirmed by a lab test). How much more is a matter for speculation until we can do serological surveys (assessing the fraction of the population that has antibodies). Government has, however, acknowledged that accounting for deaths is a problem and, as of August 12, everyone who dies suddenly including at home has to have a Covid-19 test before a death certificate is issued.

The other puzzle is why new cases peaked on July 20, when models the government was relying on predicted a peak in September. Whereas this could be an artefact of too little testing, demand for testing has also declined. Total cases on July 20: 373 628, about 0.6% of the population. When the number of active cases peaks, that indicates that the fraction infected has reached the herd immunity level. For a disease as infectious as Covid-19, the herd immunity level is about 60%. So how did this happen at a fraction of the population 100 times lower?

There is no evidence that the disease is less contagious here than anywhere else because it spread as fast here as it spread anywhere else before containment measures started. Even if testing has missed so many people that the more accurate number is 10% of the population infected by July 20, that would imply that our measures to fake a less contagious disease have cut transmission by between 50 and 60%. If the fraction actually infected is less than 10%, arriving at a turning point implies that the containment measures are even more effective than that. Some studies showing the value of masks in limiting transmission make such an early peak plausible.

There is a lot we don’t know

It is important to accept that we really do not yet know so many things we need to understand the disease at this stage. Why it seems to hit some populations harder than others, the underlying reason for particular comorbidities to be higher risk, why some who are apparently at least risk get it badly… 

The best we can do is to assess the evidence as it comes in and adjust our response based on what appears to work and what does not. It is clearer now that masks are a win. Better understanding of who is most vulnerable, favourable results from using the corticosteroid dexamethasone in very ill patients in June, discovery that delivering oxygen may be better for many patients than ventilation, investigations of clotting and vascular problems and numerous other minor improvements are likely to be major factors in the dramatic reduction in death rate since New York and Britain were hit so hard. Minor advances collectively could add up to significant improvement even if they are less dramatic than discovering a wonder drug.

If you are going to get infected, later is better — treatments are steadily improving and the odds of chaos at a hospital get lower as case loads drop and lessons are learnt.

Vaccines remain our best long-term bet for controlling the pandemic. In the meantime, we need to remember that much of our own safety is up to us — not only should we continue wearing masks in public, washing hands regularly, maintaining distance and encouraging ventilation, but we should all work on informing each other.

Confusion in countries where masks and containment measures have been politicised and where conspiracy theories have taken root have made the pandemic far worse than it should be.

We should heed the lesson of the US: open up too fast without sufficient containment, and we will be back in a public health crisis and another major economic meltdown.

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Philip Machanick
Philip Machanick is an associate professor of computer science at Rhodes University

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