The path between herd immunity and lockdown

The path between herd immunity and lockdown

In four decades working as an engineer and scientist, I have rarely known a more polarised time within the scientific field. The marketplace of ideas is depressingly split down the middle: you are either for herd immunity in the shortest possible time or for a full lockdown.

There is, however, a third way: a method that will allow the coronavirus to slowly spread within the population without causing a very high death toll and overwhelming the NHS – while, at the same time, protecting the economic and social wellbeing of the country.

How can this third way be achieved? The key is to control what the epidemiologists call the ‘basic reproduction number’ or R0-value, which is the average number of people in a fully susceptible population someone with Covid-19 infects before recovering.

Why is this number so important? Because we all have a personal R0-value over which we have direct control; by washing our hands, staying two metres apart and wearing masks. The national R0-value then keeps the score on how well the nation overall is doing these things and this determines how fast the virus spreads.

It is a fundamental tenet of control engineering that to control something you need to measure it, whether it’s the speed of a jet fighter or the temperature in a hot water tank. But measurement alone is not enough. The controller, whether a computer or a human being, needs rapid feedback without delay if the system is to work effectively.