Viral Arithmetic

The UK government announced its plan to deal with NCovid19 two days ago on 3rd March, and there has been surprisingly little comment on how enormous an epidemic HM government expects to see here.

The plan envisages the disease affecting up to 80% of the population with a 1% case fatality rate. Using the ONS's figure of  66.4 million for the UK's population (in mid-2018 -  click here ) it appears that the UK government is expecting up to 53 million cases of infection and up to 530,000 fatalities - a little short of 90% of the number of deaths that occur in the UK in a normal year (again according to the ONS - click here).

For contrast, as per the Johns Hopkins Covid19 tracker (click here), in the world as a whole around 90,000 cases have been recorded so far.  Of these around 80,000 cases of and 3,000 deaths were recorded in China, the worst affected country so far, and of these around 67,000 and 2,900 respectively occurred in Hubei, a province which has a population about 90% of the size of the UK's.  So if we are affected as badly as by far the worst affected province in China has (officially) been, we could expect about 75,000 cases of infection and maybe 3,200 deaths -  a very long way below 530,000.

Furthermore, not only the total number of cases, but also the cases per day projected by the UK government are off the scale compared to anything the world has yet seen.  Apparently, the government expects the period from the start of widespread community transmission until the peak of epidemic to be 2 to 3 months, the peak to last 2 or 3 weeks, and the wind down to be another 2 to 3 months - say 6 months or 26 weeks overall.  If there are nearly 53 million infections (80% of 66.4 million) that gives an average of about 2 million infections a week over the whole period - far more than the around 90 thousand cases in the entire world so far.

The UK government may well be unwilling to do anything that would affect the economy adversely - understandably -, and worried that taking preventive action exposes it to the risk of ridicule if  Covid19 just fades away without a major epidemic.  In this it was hardly exceptional, as we can see from Iran's initial response to the crisis, and I doubt the Chinese government was keen on shutting down their economy  Nonetheless, whatever their initial reluctance faced with reality of numerous (>1000) and rapidly increasing cases of this virus, a creaking or totally overwhelmed health care system and - therefore - the prospect of a much higher case fatality rate (maybe 1% to 3.5%) every country  has implemented drastic internal quarantine measures, and I doubt the UK will be an exception.

Update 07/03/2020

The Daily Telegraph reports that the government's plan expects 95% of infections to occur in a three month period. and 50% in three weeks.  This would fit a normal distribution with a standard deviation of 15 days.  Without implying that the government's model assumes such a distribution, this would have a daily peak of around 1.25 million cases, of which 10% are likely to require treatment.  Since the UK's medical system struggles with an average winter flu season, which peaks at maybe 1000 cases a week, and since I do not see even the economy-conscious UK government accepting a million avoidable deaths in 6 months (2% of 50 million infections) something is going to have to give, maybe in April.