There’s a key statistic about Covid-19 that you may not have heard about yet. But we can guarantee it is on the mind of every doctor and epidemiologist fighting the pandemic: R number.
What is it?
The R number is an estimate of how many people a single case of Covid-19 is likely to infect. For example, if the R Number is R1.0, it means that each person with the virus is likely to infect one other person. A true R1.0 means that the virus would spread, but not multiply. In other words, the same amount of people that were exposed to the original source of the virus would continue in the population.
An R number below 1.0 means that virus cases should decrease, eventually ending the pandemic, as the virus fails to infect at least one more person per case. That’s the goal that scientists are shooting for.
What’s the Covid-19 R Number?
The estimates of the Covid-19 R number at the beginning of the pandemic were between R2.5 and R3.0. That’s bad news, and one of the reasons why the pandemic spread across the world so quickly. Each person who contracted the virus, even those without symptoms, were likely infecting 2-3 new people, and on and on. A high R number leads to the exponential growth at the heart of any pandemic.
But social distancing measures, mask wearing, contact tracing, self-quarantine, and business closures are all proven to lower the R number. Estimates of Covid-19 R number in many countries that were aggressive with these measures were as low as R1.2 before new variants began to appear.
How do new variants affect the R number?
New strains of the virus can be more contagious or less contagious through random mutation. Obviously if a strain is less contagious than the dominant strain we’re not likely to hear about it much in the news, as it’s spreading to less and less people and theoretically dying out.
What we do hear about are the more contagious new strains. The recent UK variant is thought to have raised the R number to between R1.7 and R1.9. This is a significant jump from where it had been with the dominant strain and social measures in place, and it shows that the new strain is definitely more contagious.
Who uses the R number?
It’s likely that every government on earth dealing with the pandemic is using the R number. Why? Because it’s a great way to assess the effectiveness of public measures independent of hospitalizations and death rate. In other words, the R number doesn’t take into account how deadly the virus, or strain of the virus is. It only takes into account how easily it spreads. A lower R number is a clear, politics-free, benchmark to shoot for in what can be a messy world of information about Covid-19.
And it’s working. There are places in the world that have been extremely aggressive about social distancing and quarantine measures, places like New Zealand, and that has helped lower their R number below 1.0, to the point that they have almost completely eradicated the virus.
Immunization and R number
R number is also at the heart of understanding the need for widespread immunizations. If the virus’s R number is R1.5, but one of the people it is likely to infect is immune because they have been vaccinated, then the virus will die out, as any virus needs an R number over R1.0 to stay spreading in the population.
In other words, vaccination is a race to lower the Covid-19 R number. The more people that we vaccinate, and the more people willing to get vaccinated, the lower the R number goes. And the entire world doesn’t necessarily have to get vaccinated, just enough people to get that R number under R1.0.
This is another way of explaining the “herd immunity” concept. If enough of the world is vaccinated, we’re essentially removing targets for the virus to infect, and this can lower the R number to the point that the virus dies out.
The Immunization and Social Distance Combo
Remember, the R number of the coronavirus without any social distancing measures is estimated to be between R2.5 and R3.0. That means far more people would have to be vaccinated to get it below R1.0 and effectively begin the end of the pandemic. But social distancing, mask wearing, and other measures do lower the R number.
The virus will fall under R1.0 sooner if we stick to restrictions in place, even if we are so ready to go back to “normal”. If we get lazy now and slip up, we’re letting the virus live longer above R1.0, and, as we sadly know with Covid-19, each day the pandemic continues costs us thousands of lives worldwide.
So, the next time somebody ignorant says to you that Covid-19 is “just the flu” or “you’re healthy and you won’t get sick”, you can tell them that you’re not wearing a mask necessarily to protect yourself, you’re wearing it to protect others. You are wearing it to lower the R number and finally end this pandemic.
Let’s get through it together,
Your friends at Santo Remedio
Reference
Complexity of the Basic Reproduction Number (R0)University of Cambridge
