(CMR) Chief Medical Officer, Dr. John Lee, said that it didn’t make sense for Cayman to calculate its R-value.
Like testing, the R value is being touted as an important tool that countries can use to assess the level of threat posed by COVID-19 and, is instrumental in guiding governments actions, particularly, as it relates to the reopening of the economy.
Lee made the revelation while speaking at the daily press conference on Wednesday (May 13) advancing a myriad of reasons why the value may not be as beneficial for the island as it is for larger countries.
What is an R Value?
Lee explained that the R value or ‘reproduction number’ is a way of rating a disease's ability to spread.
“The R nought value is actually a basic reproductive number that assumes a wholly susceptible population at the beginning. So, it means that at the time there would be no suppression measures put in place whatsoever and it also assumes that there are no individuals, who either are infected or are immunised. So, you only get an R nought value at the beginning of an outbreak and it’s a model- it’s an estimate,” explained Lee.
Lee told the press conference audience that in recent times he had been getting more queries about the R value, something he thinks is gaining traction because of countries quoting the value.
“What you’ll hear of now -most countries quoting- is actually an R value which is a timed dependent reproductive number. Every day when you calculate it you will be able to find a different R number,” said Lee.
“The reason that I’ve previously mentioned, and I will say it again, Cayman has not bothered to produce this or to calculate this is not due to a lack of interest. It is actually because many of the tools that enable you to calculate it require something like a minimum of 60 cases per day or a population of 3 to 5 million to get any sensible values out of any of the estimates,” added Lee.
Lee further said that in Cayman’s case specifically, the R value would not be beneficial as the country was experiencing outbreaks in clusters as opposed to across the entire population.
“ The R value also relates to whole populations and as you are aware, we have had a number of different clusters of cases in Cayman and each of those clusters of cases will have its own reproductive number; which is different to the R value of the whole community. Actually what people want is to know the R value for the whole community,” said Lee.
“So I am saying that these clusters throw off the calculation and immediately lets you understand that when you look at a small population where there is not a lot of infection going on, it becomes a fairly meaningless figure,” added Lee.
Lee further said that there are a lot of assumptions that go into calculating an R value and these assumptions are often generated from different countries and different countries will have different experiences with the disease.
Nonetheless, Lee said he had calculated Cayman’s R number which is a very low number but opted not to share the value as he said based on the numerous assumptions it wasn’t worth quoting.
Some sources are reporting that COVID-19, officially known as Sars-CoV-2, has a reproduction number of about three, but estimates vary.
Measles which has one of the highest reproduction numbers, has a R nought value of 15.
The high R nought value for measles means that a single case requires an urgent public health response if people aren't protected through vaccination or natural immunity.