The Mutated Virus Is a Ticking Time Bomb

 Medics assess a woman for Covid-19 symptoms before taking her to a hospital

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A new variant of the coronavirus is spreading across the globe. It was first identified in the United Kingdom, where it is rapidly spreading, and has been found in multiple countries. Viruses mutate all the time, often with no impact, but this one appears to be more transmissible than other variants—meaning it spreads more easily. Barely one day after officials announced that America’s first case of the variant had been found in the United States, in a Colorado man with no history of travel, an additional case was found in California.

There are still many unknowns, but much concern has focused on whether this new variant would throw off vaccine efficacy or cause more severe disease—with some degree of relief after an initial study indicated that it did not do either. And while we need more data to feel truly reassured, many scientists believe that this variant will not decrease vaccine efficacy much, if at all. Health officials have started emphasizing the lack of evidence for more severe disease.

All good and no cause for alarm, right? Wrong.

A more transmissible variant of COVID-19 is a potential catastrophe in and of itself. If anything, given the stage in the pandemic we are at, a more transmissible variant is in some ways much more dangerous than a more severe variant. That’s because higher transmissibility subjects us to a more contagious virus spreading with exponential growth, whereas the risk from increased severity would have increased in a linear manner, affecting only those infected.

Increased transmissibility can wreak havoc in a very, very short time—especially when we already have uncontrolled spread in much of the United States. The short-term implications of all this are significant, and worthy of attention, even as we await more clarity from data. In fact, we should act quickly especially as we await more clarity—lack of data and the threat of even faster exponential growth argue for more urgency of action. If and when more reassuring data come in, relaxing restrictions will be easier than undoing the damage done by not having reacted in time.

To understand the difference between exponential and linear risks, consider an example put forth by Adam Kucharski, a professor at the London School of Hygiene & Tropical Medicine who focuses on mathematical analyses of infectious-disease outbreaks. Kucharski compares a 50 percent increase in virus lethality to a 50 percent increase in virus transmissibility. Take a virus reproduction rate of about 1.1 and an infection fatality risk of 0.8 percent and imagine 10,000 active infections—a plausible scenario for many European cities, as Kucharski notes. As things stand, with those numbers, we’d expect 129 deaths in a month. If the fatality rate increased by 50 percent, that would lead to 193 deaths. In contrast, a 50 percent increase in transmissibility would lead to a whopping 978 deaths in just one month—assuming, in both scenarios, a six-day infection-generation time.

Transmissibility increases can quickly—very quickly—expand the baseline: Each new infected person potentially infects many more people. Severity increases affect only the infected person. That infection is certainly tragic, and this new variant’s lack of increase in severity or lethality thankfully means that the variant is not a bigger threat to the individual who may get infected. It is, however, a bigger threat to society because it can dramatically change the number of infected people. To put it another way, a small percentage of a very big number can easily be much, much bigger than a big percentage of a small number.

I dismissed the news initially because viruses mutate all the time and there have been too many baseless “mutant-ninja virus” doomsaying headlines this year. The exaggerated, clickbaity alarmism makes it harder to discern real threats from sensationalism. Given the constant reality of mutation, genomic variants should be considered innocent until proved guilty. Even an increase in the proportion of cases attributable to a particular variant is not definitive proof of an evolutionary advantage.

However, as data on the new variant roll in, there is cause for real concern. Trevor Bedford, a scientist at the Fred Hutchinson Cancer Research Center and a board member for the Covid Tracking Project at The Atlantic, points out that infections from the new variant are increasing very rapidly among the population in the U.K. Bedford also notes that this new variant seems to have a higher secondary-attack rate—meaning the number of people subsequently infected by a known case—compared with “regular” COVID-19.  Finally, the new variant seems to result in higher viral loads (though this is harder to be sure about as viral loads can be affected by sampling bias and timing). As Kucharski told me, all of this does not rule out other explanations. This increased transmission could be due to chance or founder effects—meaning one variant just happened to get somewhere before the other variants and then got “lucky”; it was early, rather than more transmissible. It could be due to changed behavior among people—quarantine fatigue, less masking—leading to more rapid spread. However, given the current evidence, along with the specifics of the mutation, it’s getting harder to assume that those other explanations are more likely than the simple proposition that this is truly a more transmissible variant.