An explanation of confusing coronavirus terminology

AT THE daily COVID-19 press briefings we see lots of graphs and hear talk from the government advisors about ‘following the science,’ and the modelling that has been done to predict and monitor the pandemic.

We also hear about the

‘R’ value, flattening the curve, the peak and the daily number of deaths from COVID-19. It can be very confusing.

So first, let’s consider what is meant by flattening the curve. Essentially, in the epidemiological model used there are two possible progressions for COVID-19. One line will show what happens to the number of cases if you do absolutely nothing, and the other if you implement preventive measures like social distancing and self-isolation to slow the spread and ease the pressure on the health service.

In the first the curve goes up and up, with admissions and deaths rising exponentially. In the second when you take preventive measures you flatten it out and make it as shallow as possible, so that the peak is more manageable and creates far less suffering and less deaths. That is needed to get on top of it.

Models of COVID-19 that are used include a technique known as the Markov Chain Monte Carlo (MCMC) method. Essentially this considers a chain of possible events in which the probability of each event depends on the state attained in the previous event.

This is used in conjunction with the SEIR model. This tracks the flow of individuals through four series that account for age specific patterns of transmission.

The stages are: susceptible (s), exposed (e), infectious

(i) and recovered (r). The epidemiologists can throw all sorts of preventive measures and possible factors into complex equations and crunch the numbers to simulate how the different interventions can affect the pandemic life cycle.

Finally, the R0 number. This is the symbol for the basic reproductive number, which measures how many people are infected by one person.

If the R0 number is 2 then one person passes it to two people. Those two infect four, those four infect eight and so on. That is an exponential rise and the curve shoots up.

Social distancing should bring the number to less than one.

When that happens one person is less likely to infect another person, which is what we need to achieve.