Coronavirus : Update 3 from the Epicenter
Apologies for the change in tone, but I felt compelled to write something regarding the science driving the response to the virus in the UK, which is different to the way the rest of the world is handling it.
Like China, Italy saw an explosion of cases in a concentrated area of the country which quickly overwhelmed hospitals. Both countries ring-fenced those busy towns in order to avoid the uncontrolled spread of the disease. The level of China’s military crackdown allowed them to stop there, whereas Italy’s democratic government had not choice but to extend the quarantine to the whole country once they realized that so many people were fleeing the red-zone…
It’s too early to tell exactly the effect on transmission that grounding 60 million people will have, but it seems likely that the infection will run its course for those who already have the virus. The rest of us will be spared… for now.
The issue with this approach is that the virus isn’t going anywhere soon. Lengthy, draconian, widespread quarantines may even temporarily eradicate the disease from a country, but it will only take a contagious traveler to land in Rome or Beijing in September and the whole things kicks off again.
What we really need is a vaccine, but while we’re waiting, the UK is implementing a plan to avoid Italy and China’s likely secondary epidemic. They are attempting to induce Herd or Community Immunity on a UK-wide basis.
The idea is simple : if enough people are immune to something, then the likelihood of contagious person infecting someone without immunity is reduced to near-zero. This graphic from Wikipedia explains it nicely :
Now, in order to achieve Herd Immunity, a population must achieve a certain level of immunization saturation. The exact effect level depends on how contagious the disease is. Measles for example is incredibly contagious, and in order for Herd immunity to work you need >95% of the population to be vaccinated.
COVID-19 has lower transmission rates and so a community could be protected with only 60% of the population immune. Unfortunately with no available vaccine, that means waiting for 40 million people to get sick. With average mortality rates looking to be between 1 and 3%, the UK would therefore have to sacrifice up to 1.2 million people to achieve it’s goal.
So is Boris a psychopath? Well, possibly not. You see, those numbers are only likely if the epidemic is uncontrolled. In an ideal world (as Prof Graham Medley, Chair of the Scientific Pandemic Influenza Group on Modeling explains in this video : https://youtu.be/blkDulsgh3Q) we would take all the vulnerable people to the north of Scotland, let the epidemic play out in the rest of the UK, and then reintegrate the vulnerable. The result would be Herd Immunity with next-to-no loss-of-life.
The real-world scenario doesn’t look quite that rosy however. The government’s plan appears to be to allow the epidemic to spread slowly but completely through the country, whilst trying to keep the vulnerable from becoming infected through well-timed self-isolation.
It’s easy to backseat drive in a situation like this, but from the outside this looks a little idealistic – if not downright dangerous. The following graph comparing test results by age group between South Korea (who is rigorously testing everybody) and Italy (who is only testing the sick), shows that the highest levels of infection occurs in the 20-29 age group, who are infectious but asymptomatic :
In other words, unless you’re testing everyone, it’s going to be next-to-impossible to time self-isolation correctly. Nobody is going to see a wave of illness encroaching on a neighborhood, and mortality statistics lag a month behind infections, so it’s likely to be too-little too-late.
In Italy most of the cases are concentrated in just one region, but we’re losing about 200 people a day – a number likely to rapidly accelerate as new cases continue to rise exponentially. What is happening here is proof of the danger of getting the timing wrong by just a few days.
So, is it better to try and stop the spread while we look for a vaccine, or do we think the government can control the transmission with the precision of a computer model? I know which side I would err on…