There is another term being used a lot in media discussions recently known as an “R-value.” It is not a new term, but for most of us has never been relevant. Today, we will walk you through what this value denotes, the two different manners in which this number is utilized, and how it pertains to the current pandemic.
When discussing R-values, it is important to distinguish between R0 (pronounced “R naught”) and R. R0 is known as the basic reproduction rate. This term is a measure of how infectious a pathogen (such as a virus) is when dealing with a naïve population. This term therefore is primarily applicable at the beginning of a pandemic as it spreads to new regions that have never seen it prior. The R value they have been discussing in the media is different in that it applies to the current state of affairs now that the virus has been prevalent in society for some time.
With respect to the R0 for COVID-19, we have at best an estimate at this time. This is largely due to the lack of available testing at the onset. The estimates of R0 for COVID-19 range from 1.4 to 5.7. What that means is that in a population that never experience COVID-19 would expect that each individual who got COVID-19 would spread it to 1.4 to 5.7 other people. There are numerous factors that play into how high this value is for a given pathogen even at baseline – how dense the population is, method of spread, the inherent contagious capability of a pathogen to name a few.
While the R0 for COVID-19 will one day be nice to know as a means of comparison to other pathogens, the current R-value is of more significance as it lets us know what the current state of affairs is and permits us to manage the situation to some extent. We have been advised that the population needs to see an R-value less than 1 to know there is less disease. To clarify what this means, we will take a quick peek at China’s former “One-child policy.” In the late 1970’s, China faced issues related to overpopulation and instituted a policy permitting couples to only have one child. In the early 1970’s, the average couple had 5 children in China. That would be the equivalent of an R-value of 2.5. As you can imagine, a population increases rapidly in size when this occurs as it is more than a doubling every generation. The one-child policy made it law to enforce an equivalent R-value of 0.5. That means that every generation the population would be half the size of the prior. Within the last decade, the rules were relaxed to permit two children per couple, and R-value of 1. The expectation then would be each generation the same size as the prior.
The published Federal Government plan for Opening Up America Again (https://www.whitehouse.gov/openingamerica) follows this concept. What it seeks to see is a reduction in cases over a two-week period in a given region to make it permissible to reduce restrictions in a step wise fashion. This correlates to an R-value of less than 1. It is predicated on being able to perform a lot of testing to ensure that the lessening of number of infections is occurring in the first place and to closely monitor the effects of reduction of restrictions once the two-week criteria is met. It is near a given that the number of infections will initially rise when people are out and about again. The key is that in doing so, the R-value stays below 1. If that value gets above 1, the plan calls for a return to the prior phase of restrictions to again exert greater control over the spread of the virus.
Is this plan perfect? Likely not, but it is very reasonable. One aspect that is questionable is the timetable for there being a decrease without addressing exactly how much the decrease needs to be. If you accept an R-value of 0.99 as a decrease to permit moving to the next phase, it is a near given that you will be above 1 almost immediately and have to take a step back. Germany, as an example, was at an R-value of 0.7 before reducing restrictions and has now returned to 1. Do we need to be more aggressive? Should we set a threshold R-value along with a duration? Should this threshold be different for more densely populated regions where contagion is more likely?
And then there is the other issue….while the Federal Government stated this as the plan, there are states that have chosen to ignore them and reopen their economies despite not meeting the criteria. Will this change the long-term outcome for their region? Hindsight will one day yield the answer. If there is an effective treatment or vaccine in the short-term, the answer is they will have experienced additional fatal outcomes. If it takes a long time for such remedies, it will mean they got it over with faster and resumed their lives. As always, glad not to be a politician on this one.
Stay safe all!