A very tricky virus
What is it that makes Covid-19 so dangerous?
At the bottom of the South Pacific, in our remote and comparatively comfortable bubble, it’s difficult to get a sense of how serious Covid-19 really is. As I write these words, we have had 1,503 cases and just 21 deaths. We just shut down our entire economy, and many will ask whether it was necessary, or worth the multi-billion-dollar bill. Is this virus really that bad?
The numbers that we see from around the world – the number of cases and the number of dead – are staggering, but abstract. It is difficult to know what they really mean. Is this disease really any different from the seasonal flu? After all, flu kills people every year and we don’t shut our economy down every winter to stop it. What about car accidents? We don’t stop driving because of road deaths, or eating junk food because of heart disease. What is it that makes this disease different?
There are a few statements I’ve heard in the media about the coronavirus which stand out to me. The first was on the BBC, a quote from statistician David Spiegelhalter, where he agreed that the virus was like the flu, if the flu was “twice as contagious and ten times as deadly”. We are a long way from being able to put accurate numbers on this virus, as he himself has said, but I found that a compelling comparison.
Two quotes from New Zealand, though, warrant further discussion, as they make very illustrative points. The first was a piece of feedback from a Radio New Zealand listener, criticising aspects of the lockdown, who said “it’s not Ebola”. The second was from Dr Ashley Bloomfield, where he said “this is a very tricky virus”.
The first quote – it’s not Ebola – was presumably intended to indicate that Covid-19 isn’t so terrible, as it was accompanied by a complaint about the strictness of the rules in place to control it. However, having read rather a lot about Ebola[1], what it says to me is that many people don’t understand what is terrible about either the Ebola virus or Covid-19.
Ebola captures the imagination as a truly horrific disease, a reputation fuelled by lurid and not strictly accurate books such as The Hot Zone and movies such as Outbreak. It has a very high fatality rate – in one of the early outbreaks it killed about 90% of those infected, and in subsequent outbreaks the death rate has ranged from 25-90%. It also has no vaccine and is difficult to treat, which makes it a more dangerous disease, if you catch it, than something like plague. Plague in all its forms (bubonic, pneumonic and septicaemic) has a fatality rate of 30-100% without treatment, but it’s a bacterial disease and responds to antibiotics, and there’s a vaccine available too.
Ebola is rightly a much-feared disease, and clearly much more deadly than Covid-19, but it is different in other ways as well. Most importantly, Ebola differs because it is not as contagious. There have been some awful outbreaks, and under certain circumstances it is difficult to control, but it is far less likely than many other diseases to turn into a global pandemic. Every time it has got out of control, it has been because specific hygiene practices, or a lack of them, have put people at risk. Mostly, it has spread in desperately under-resourced hospitals, where equipment may be reused without adequate sterilisation. In the first recorded outbreak, linked to a missionary hospital near the Ebola River, it was probably the reuse of hospital needles that contributed to much of the spread. In the worst recorded outbreak, in West Africa from 2013-2016, it was spread when family members prepared the bodies of the dead for burial.
Ebola spreads by direct contact with bodily fluids such as blood, similar to a disease like Hepatitis B. This method of transmission means that it is never likely to spread far in a country with a well-resourced medical system. That’s obviously very different from Covid-19, which has been devastating in a number of very wealthy countries. That brings me to the final quote “it’s a very tricky virus”.
A disease like Ebola makes people very sick very quickly. Someone who is infected isn’t likely to go to school or work, visit bars, restaurants or rest homes, attend a wedding or go on a cruise. They know that something is horribly wrong, and most people seek medical help as soon as they can. With Covid-19, it’s a different matter entirely. About half of those who are infected with the virus have very mild symptoms, and people can also be infectious a couple of days before they show any symptoms at all – during the incubation period. As a result, people with Covid-19 can be out and about, infected and unaware.
If Covid-19 spread like Ebola, it wouldn’t matter so mcu if infected people were out shopping, or at work, or at school, or on a plane. In the course of a normal day, we don’t normally come into contact with other people’s bodily fluids, unless our job involves caring for people who are very young, old, disabled or sick. But Covid-19 is spread through droplets of moisture from the lungs – droplets that are expelled when someone coughs, speaks, or even just breathes out. These droplets, too small to see at around one hundredth of a millimetre in size and carrying virus particles one hundred times smaller again, can infect someone nearby by landing in their eyes, nose or mouth. Droplets also land on surfaces, where they can be picked up when someone touches a surface and then touches their eyes, nose or mouth. There is some evidence that the virus can be spread on even smaller particles which travel further, but most of the transmission seems to be associated with respiratory droplets, which travel about a metre.
One of the main symptoms of Covid-19 is a dry cough, which increases the chance of transmission, as droplets from a cough (even a dry cough) travel further. But Covid-19 can even spread during its incubation period, before an infected person shows any symptoms at all.
This combination of droplet transmission and infectious people going on with their daily lives is what makes Covid-19 so tricky, and so dangerous. A virus which spreads so easily doesn’t need to have the fatality rate of Ebola to cause a deadly pandemic. Even if it kills just one in a hundred of those infected (which is just a guess given how new this virus is) it could still kill millions, just because so many people will be infected.
But that still doesn’t tell us how bad it really is. After all, people die all the time from all sorts of causes. Given that many of those who die from Covid-19 had other health problems, what’s to say they wouldn’t have died anyway, from a heart attack, from a stroke, or from the flu?
One of the most meaningful ways to look at the deaths caused by Covid-19 is to compare the numbers with those for other causes of death. Looking at New York, currently the worst affected state in the United States, gives a picture of just how horrifying an uncontrolled outbreak of Covid-19 can be. Heart disease is usually the leading cause of mortality there – killing 44,000 people in 2017. Cancer killed 35,000 and accidents, the third most common cause of death, just under 7,700. Flu and pneumonia, to which Covid-19 is often compared, killed 4,500. Over the previous four years, the highest number killed by flu was just under 4,900.
In comparison, Covid-19 is reported to have killed just under 22,800 people in New York state, since the first deaths were reported on the 14th of March. In comparison, assuming that deaths from all causes are spread evenly over the year, New Yorkers could have expected around 7,600 people to die from heart disease, 6,000 to die from cancer and 1,300 from accidents. Flu deaths are seasonal, so it’s an untrue assumption that the deaths would be spread evenly over a year, however, on average, there would be around 800 flu deaths over that period. This makes David Spiegelhalter’s quote about Covid-19 being ten times as deadly as flu look like a huge underestimate. These very rough figures suggest it is more than 28 times as deadly.
But those figures don’t tell the full story. There is a more meaningful figure known as excess mortality. This figure is derived from comparing the total number of recorded deaths during the time of a disease outbreak to historical averages for the same time period. And comparisons illustrated by excess mortality are even more startling.
The most recent figures on excess mortality for New York state cover only the period from the 14th of March until the 2nd of May, by which time the state had reported around 18,800 Covid-related deaths. However the CDC estimated that 24,000 more people than expected had died during that time, a difference of over 5,000. The main reason for that difference is thought to be the way that deaths are reported, although it’s also possible that people aren’t seeking medical attention as promptly due to fear of Covid-19, that treatment is compromised due to the overloaded health system, or that the control measures against Covid-19 – primarily lockdowns – are contributing to the loss of life.
Globally, the data on excess mortality are just as shocking. For London, deaths are more than double (135%) what would be expected. In Italy, by the end of March – which is a very long time ago in terms of the pandemic – deaths were up by 55% across the country, but in Bergamo, one of the worst affected provinces, there were six times the usual numbers of deaths (496%). Similar figures are seen in other badly-hit areas – deaths at five and a half times the normal rate in Guayas, Ecuador, nearly three times normal in Manaus, Brazil (178%), five times normal in New York city, more than double in Ile-de-France and nearly double in Stockholm.
These increases in mortality are not seen in countries with fewer cases and strict lockdowns, supporting the argument that the excess mortality is caused directly by Covid-19, or because people were not able to be treated for other conditions, and not as an indirect effect of lockdowns.
Excess mortality tells us something else - that deaths associated with the pandemic are undercounted, by tens of thousands. Across 22 countries with Covid-19 outbreaks, the New York Times has reported 74,000 deaths in excess of historical averages and not recorded as being caused by Covid-19. In the UK, with 36,500 reported Covid-19 deaths by May 1st, there were another 16,700 deaths which were over the average.
But the number which speaks to me most directly about the real human tragedy of this pandemic is actually much smaller. It’s not exact because it isn’t covered by official reports. We know it is over a thousand, worldwide, but country-specific data are rare. We know that of that thousand, around 170 were in the UK, somewhere between 35 and 65 were in Spain and well over 150 were from Italy. This number represent the healthcare workers who have caught Covid-19 from the patients they are treating and have then died. It’s a staggering loss for health systems which are already overwhelmed.
More than anything, to me this shows just how horrible the situation must be in the worst-affected areas. We just don’t expect this kind of thing to happen in wealthy countries with well-resourced medical systems. There’s no expected mortality for healthcare workers who catch diseases from their patients and die. When it happens, just once, it means that something has gone wrong. When it happens over a thousand times, it shows that a combination of Covid-19 and complacent, indecisive government has pushed health systems to the brink of collapse.
With a health system overwhelmed by Covid-19, a country becomes like the human body in the late stages of AIDS – unable to fight back against a myriad of diseases it would normally shrug off. Covid-19 is deadly not just because it kills people directly, but because it cripples the very system we need to fight it. And that makes it a very tricky virus indeed.
[1] There are many books which talk about the Ebola virus, but if you just read one, I recommend Spillover: animal infections and the next human pandemic by David Quammen (The Bodley Head, 2012). As a bonus, there is a very good overview of the 2003 SARS outbreak – that is the outbreak which gives lie to the statement that nobody could have predicted the current pandemic.
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