Researchers in the United Kingdom identified a new variant of the coronavirus earlier this month—one that appears to be around 56 percent more transmissible than the more common strains that have been afflicting humanity for the past year. While we have seen no evidence that this strain causes more severe illness, it could nevertheless ramp up the deleterious consequences of the pandemic dramatically.
London School of Hygiene & Tropical Medicine epidemiologist Adam Kucharski offers some simple calculations to illustrate why a COVID-19 variant that is 50 percent more transmissible is likely to be a bigger problem than a variant that is 50 percent more deadly.
Kucharski begins by assuming that the basic reproduction number (R0) of COVID-19—that is, the number of people on average to whom an infected person will pass along the disease—is 1.1. If R0 is above 1.0, the virus will continue to spread. When R0 is below 1.0, the virus will stop spreading. As it happens, the R0 for the U.S. has indeed been hovering around 1.1 recently.
Kucharski then assumes an infection fatality rate (IFR) of 0.8 percent. While calculated IFRs vary considerably among the various states, this assumption is similar to Indiana's roughly calculated IFR of 0.73 percent in late November.
So assuming an R0 of 1.1, an IFR of 0.8 percent, a generation time of 6 days and 10,000 infected people, Kucharski calculates that we would expect 129 eventual new fatalities after a month of spread. Increase the IFR by 50 percent, and that changes to 193 new fatalities after a month. Keep the IFR at 0.8 percent and increase transmissibility by 50 percent, and the number of new fatalities after a month jumps to 978.
Those are just illustrative calculations. Kucharski's key message is that "an increase in something that grows exponentially (i.e. transmission) can have far more effect than the same proportional increase in something that just scales an outcome (i.e. severity)."
In a preliminary and not yet peer-reviewed study, London School of Hygiene & Tropical Medicine epidemiologist Nick Davies and his colleagues warn, "The increase in transmissibility is likely to lead to a large increase in incidence, with COVID-19 hospitalisations and deaths projected to reach higher levels in 2021 than were observed in 2020." But there is a way to blunt a resurgent pandemic: vaccination. "It may be necessary to greatly accelerate vaccine roll-out to have an appreciable impact in suppressing the resulting disease burden," they conclude.
Since the new more transmissible variant has already spread outside of the U.K., it is unlikely to spare the U.S. Our public health authorities need to "stop dawdling and make sure COVID-19 vaccines are available to everyone sooner rather than later."