‘This pestilence was so powerful that it was transmitted to the healthy by contact with the sick” wrote Giovanni Boccaccio of the Black Death, in his preface to The Decameron. The trouble with the coronavirus is almost exactly the opposite – it is transmitted to the sick by contact with the healthy. The people most at risk of dying are those who already suffer from underlying illnesses. And evidence is accumulating that the virus is passed on very early in the progression of the disease, often when you are still without much in the way of symptoms.
The arrival of fast and reliable mass antibody testing, this coming week with luck, should be a game changer. It will enable those who have had the virus and recovered to be identified and licensed to resume normal life. How long their immunity lasts is unknown, but there is a good chance it will be many months at least.
Once antibody testing and more widespread virus testing roll out we will find out just how widespread the virus is among those with no or few symptoms. Only then can we know for sure what the case fatality rate is, but the best guess is that it will be well below one per cent overall, though up to 10 per cent in elderly cohorts.
Some people show almost no symptoms – and this seems to be especially true of children. “Children are at similar risk of infection as the general population, though less likely to have severe symptoms,” says one Chinese study. Those who do get symptoms report a dry cough, fever, aches, fatigue and often – perhaps even in the absence of other symptoms – a sudden loss of taste and smell.
The first few days are often mild, but – in contrast to Sars – this is when you are most infectious. “High transmissibility of Covid-19 near symptom onset suggests that finding and isolating symptomatic patients alone may not suffice to contain the epidemic,” concludes one study. By contrast, unlike flu, it seems to be most severe and dangerous in the second week, with people needing hospitalisation somewhere between day nine and day 12 if at all. It is killing almost twice as many men as women, perhaps because men seem to generate fewer of a key antibody type, immunoglobulin G.
The virus is very contagious. A person with Covid-19 produces a thousand times as many viruses as somebody with Sars would do. On average he or she gives it to more than two people in the absence of social distancing. But averages mislead. Some super-spreaders give the virus to 50 or more people. It is not clear why: they could be less sick and so more sociable, or just loaded with more virus. One of South Korea’s advantages here is that in 2015 it had an outbreak of the Mers coronavirus and learned a lot about superspreaders and the value of tracing all their contacts.
Most infection seems to occur indoors and worryingly quite a lot may have happened within the medical system especially in Italy in the early weeks. According to one study, on tissue paper the virus survives less than three hours, on wood and cloth two days, on glass and banknotes four days and on stainless steel and plastic a week. The hope that it would die down during the summer is fading. As one team of scientists argues: “there is no evidence to suggest that warmer conditions in northern hemisphere summer months will reduce the effectiveness of Sars-CoV-2 transmission”.
The pandemic is not under control yet. Since March the global death toll has doubled in six days twice. At that rate it would kill more than 600,000 people by the end of April and 10 million by the end of May. But of course that will probably not happen because interventions will have an effect – and predictions based on models are all over the place. Countries that have imposed strict national lockdowns are beginning to see the curve flatten, though not as fast as expected. Italy’s death toll shot up again on Friday despite people being confined to their homes for nearly three weeks.
The measures that will bring this nightmare to an end include: first, more and better testing, and the tracing of every contact that an infected person makes. What makes it possible in the modern world is the digital footprint we all leave behind: privacy concerns will have to be put on hold. Second, more and better treatment of those who get ill, including more ventilators but also experimental repurposing of drugs including anti-HIV drugs and antimalarials such as chloroquine. Third, the use of monoclonal antibody drugs specifically designed to fight the virus. Fourth, probably some time next year, a vaccine.
As research progresses, the picture is becoming ever clearer. The more we learn, the nearer a solution becomes.
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