The key number missing from the public discourse on Covid 19 was mortality rate. Only if that was high did Covid 19 Virus justify the response and until now the estimates have been flaky and unconvincing. Today, the UK Government advisors said it was 1%. Not sure how they got there but here is one possible way.

One way to know the mortality and infection rate of a virus is to find a sample population, expose them to the virus and measure the result. This is nearly exactly what happened on the cruise liner Diamond Princess which was held in quarantine in Japan. Everyone was exposed, probably everyone who was infected was detected as such. The 7 who died were not already ill in hospital from something else. For these reasons the data from Diamond Princess is worth a look.

Also, the Centre for Disease Control (CDC) publish numbers for every year for ordinary seasonal flu in the United States. The 2017-18 (ie before Covid 19) numbers show that of 327 million Americans, 45 million (14%) got seasonal flu, 810,000 (0.25%) needed hospitalisation and 61,000 (0.02%) died. The 2017-2018 numbers, which remain provisional, are almost double the average of previous years. It could be the estimates will be refined down, or just perhaps, Covid 19 was out and about before it was being measured and detected. I am really curious about this. The data is steady for about 8 years then leaps in 2018-2019. Of course, the consensus view is that Covid 19 started in Wuhan in about October.

On Diamond Princess there were 3711 souls and of these 705 (19.5%) got infected with Covid 19 and of those 7 ie (1%) died. So overall 0.2% of the exposed population died but mortality is more normally expressed as a % of those infected so 1%. This number is also what the Prime Ministers Medical expert announced.

So it would seem that the chance of catching Covid 19 is about 50% higher than normal seasonal flu.

However, the mortality rate of Covid 19 would seem to be about 50 times greater than seasonal flu. (seasonal flu) 0.02% to (Covid 19) 1%. Some are arguing the Diamond Princess mortality rate is higher because older people go on cruises. I question that since the average age of people on Cruises is 46 according to the Association of Cruise liners.

So what. Of course, it always dramatic to quote percentage increases of small numbers and these are quite small numbers. Covid 19 does seem more dangerous than seasonal flu, but the mortality rate is less than SARS (10%) and much less than Ebola (40%).

It is quite rightly a political decision whether to shut down public life and personally I thought Prime Minister Johnson did a good job of explaining his policies. Watch the you tube in full not the 4 mins the BBC chose. Starts at 25 mins 54.