If the new strain is 50% more infectious, then the mitigation measures
The mutated strain of the coronavirus identified only recently in England is likely to have already spread throughout the United States, experts said Tuesday, even though it’s only been officially detected in isolated pockets of a handful of states so far. The strain is much more transmissible than the previous dominant strain, the latest evidence shows, and if something isn’t done quickly to rein in its spread, the pandemic could become dramatically more deadly on a daily basis.
The new strain, also called a variant, has not evolved to be inherently more deadly nor cause worse symptoms. But because it spreads more readily, it fuels an exponential spike in cases, as occurred in England, and the end result will be a burgeoning death toll in subsequent weeks.
Only stricter prevention measures across the country, or far faster deployment of vaccines (the new strain is not expected to evade vaccine effectiveness), are likely to prevent a significantly worsening catastrophe. Otherwise, expect 100,000 to 150,000 more U.S. Covid deaths by the end of February, says Ashish Jha, MD, dean of the Brown University School of Public Health.
Jha called the new strain “deeply worrisome.”
It’ll become dominant
The variant is thought to be between 40% and 70% more infectious than its coronavirus kin. Several experts have settled on 50% as a likely figure, and lingering doubts over whether it really was more infectious have largely faded. It’s expected to crowd out the previous dominant strain, through sheer speed of infecting new human hosts, and become the main one in circulation.
“The new strain is estimated to represent about 1% of all infections at this moment but because of its increased contagiousness, the best estimates are that it will become a majority of all new infections by March,” Jha says in a statement.
The expected spike in new cases could cause the death toll in a given population to spike six times higher than with the previous strain, other things being equal, says Adam Kucharski, a mathematician and epidemiologist at the London School of Hygiene & Tropical Medicine.
Meanwhile, as U.S. vaccine deployment lags far behind what was planned, most coronavirus testing efforts are not yet focused on determining if a given infection involves the new strain. But scientists have seen this movie before.
“It is, at this point, almost surely too widespread to be contained in any specific state or region of our country,” Jha says. “This new variant is significantly more infectious, threatening a rapid increase in rates of new cases and a much, much more deadly and destructive pandemic. This demands an urgent rethinking of our current policy responses.”
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Mutations are normal, but…
It’s normal for a virus to accumulate mutations that can cause its behaviors to evolve, though many mutations lead to no notable or important differences. The U.K. strain, called B.1.1.7, was detected in September and viewed as a problem by early December. Among its many mutations are increased effectiveness of the spike proteins that glom onto receptors on human cells, allowing the coronavirus guts to slip in and use the human cell machinery to reproduce, which leads to sickness. (Another strain has developed in South Africa, but the main focus and worry right now is over the U.K. strain).
“This new, more infectious variant will change the underlying dynamics of the pandemic, with exponential growth in infections making the virus vastly harder to contain and overburdening our stressed health care system,” Jha says. “Without significant changes in behavior to once again ‘flatten the curve,’ each new case will result in a greater number of subsequent infections than in the past, making superspreader events more likely and more risky, and making even smaller outbreaks more explosive and harder to contain.”
Such a surge would also have widespread additional economic repercussions, Jha and others warn.
The new strain has been detected in four U.S. states as of this writing. But most testing efforts aren’t looking for it yet.
“It’s probably more widespread than we think,” says Marc Lipsitch, PhD, a professor of epidemiology and director of the Center for Communicable Disease Dynamics at Harvard T.H. Chan School of Public Health. There’s good reason to expect it will spread rapidly here, just as it has in the U.K., Lipsitch told reporters today. “It’s a big deal for a world that’s already stretched trying to control the old variant.”
How the math works
The original coronavirus strain was thought to have a reproduction number of about 3, meaning each person infected would infect three others, Lipsitch explains. That’s a very rough estimate that varies greatly depending on the individual and a range of circumstances. But through lockdowns, masks, and other prevention efforts, the number was reduced to 1 in the late spring and early summer — the average infection led to just one more infection, so the number of new cases leveled off.
If the new strain is 50% more infectious, then the mitigation measures that lowered the original strain’s reproduction number from 3 to 1 will lower it to only 1.5 for the new strain, Lipsitch says. Roughly speaking, he says, if each infection generates 1.5 additional cases, then in less than 2 weeks cases double, and in a month or so there would be four to five times as many cases.
“It might be a little faster than that,” Lipsitch says. “If we don’t change our control measures, once it becomes common it will accelerate transmission considerably.”
Another way of looking at it: To get the reproduction number down to 1 as the new strain becomes the dominant one, contacts with infected people would need to be cut by one-third, he says.
Though he had hoped Americans might return to some sense of normalcy by summer, the new challenge means control measures will be needed for longer, Lipsitch says. He’s advising health officials to use existing tools that can help identify the new strain, then focus contact tracing on people infected with this more worrisome variant. His message to you:
“If you are identified with that new variant, then your isolation and quarantine and contact tracing is considerably more important,” he says. “You’re doing more for the world, for the people you care about, by isolating yourself and cooperating with contact tracers than even before.”
And, as other health experts continue to plead: Mask up, hunker down as best you can, and know that this pandemic is far from over.