COVID-19: The Difference Between The R Number & K Number
For weeks and even
months, we have been hearing the term R number in regards to the spread of the
Covid-19 Pandemic. But as lockdowns are being lifted around the world, there is
a new metric increasingly referred to by news anchors, experts, and politicians
- the K number.
Both of these values
are carefully calculated by mathematicians and scientists after gathering and
analyzing vast amounts of data. The experts collect hospital and ICU
admissions, deaths, self-reported symptoms, and behavior surveys to estimate
the R and K numbers, each one of them representing slightly different insight
into the virus ad how to combat it.
The R Number
The R number also referred to as R0, is the basic
reproduction number. It represents the number of people an infected person goes
on to infect. It’s influenced by the characteristics of the disease (in this
case Covid-19), mainly how easily it is passed from person to person. If the R0
is larger than one, that indicates the number of infected people is rising.
Human behavior, such as self-isolation, mask-wearing, and following social
distancing guidelines, will also impact the R number. The ultimate aim of all
these control strategies is to bring the R0 below 0, which indicates the number
of infected people is declining.
While the R number can help indicate if lock-down measures
are working, it doesn’t quite show us the full picture. The R0 indicates
if an epidemic is getting bigger or smaller, but not how large it is. “R
should always be considered alongside the number of people currently infected. If
R equals 1 with 100,000 people currently infected, it is a very different
situation to R equals 1 with 1,000 people currently infected.” as explained in
the UK government website.
The
K Number
The K number is a metric used to
shed light on the variations of R0 across different Covid-19 cases. Rather than
assuming that every infected person and every contact they make follows the
same pattern (as with the R number), scientists working on epidemic models
allow for the number of new cases caused by each infected person to vary.
For example, if a person self
isolates immediately after contracting the disease, they are likely to infect
fewer people than someone who attends a gathering. Many people, although
ill and highly infectious, don’t show symptoms at all. They might make many
contacts without realizing they pose a danger to others. The K value shows how
much statistical variation there is in the spread of the virus. Small
values of K mean that one infected person can trigger many new cases in a very
short time.
“Once K is below one, you have got the potential for super-spreading.”
As lockdown measures ease in the following week, it will help scientists identify what’s more likely to lead to super-spreading - restaurants, the use of public transportation, or mass gatherings like concerts and weddings, etc.
Both the R number and the K number are needed to understand how Covid-19 spreads, which areas of life are safe to resume, and which ones must remain on hold for our safety.