By Amy B. Rosenfeld and Vincent R. Racaniello
Dr. Rosenfeld and Dr. Racaniello are virology professors at Columbia University Vagelos College of Physicians and Surgeons.
News headlines and health experts on social media are sounding the alarm over another variant of the coronavirus, this time Delta, claiming it is much more contagious and perhaps more lethal than any other variant seen so far. It’s easy to understand why: New variants of the virus continue to emerge, and cases are rising in many countries. But whether new variants pose a unique or substantial risk is still unknown, and as virologists, we are concerned that misunderstanding variants and the risk they pose can cause confusion and panic.
As the coronavirus spread globally, its genome changed — mutated — as expected for any virus. These mutations may affect the virus’s “fitness,” its ability to reproduce and spread. Some mutations weaken a virus, some have no measurable effect, and some make it stronger.
As a virus becomes more fit, it will outcompete less fit viruses — and Delta is not the first variant that has beat its predecessors and competitors in certain areas. There’s the Alpha variant that first became dominant in Britain, and the Gamma variant that first became dominant in Brazil. Such changes are not unique to the coronavirus. Increased viral fitness happens during every flu season and is why some flu variants may circulate more widely than others.
Just because a variant displaces another does not necessarily mean it is more infectious or more deadly to the people who become infected with it. As has been true for the past year and a half, human behavior is far more important in shaping the course of the pandemic than any variant.
There are many ways that a virus can mutate to increase its fitness. While there’s been much focus on changes in the virus’s spike proteins, which allow the coronavirus to invade cells, a virus can also sustain changes in other proteins. Such changes can allow the virus to replicate more easily or evade the immune system, for example. They may even allow the virus to persist longer in nasal passages.
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