There are many unknowns about the variants, but human activity, including getting vaccinated, is far more important in shaping the course of the pandemic.
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 of 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.
Determining what impact a given mutation has requires substantial laboratory research. Sometimes, early conclusions about a particular mutation can be incorrect. When the first variant of note, D614G, emerged last winter, some scientists believed changes to the virus's spike protein made the virus more contagious. But subsequent research showed that was not the case. Even so, each time a new change in the spike protein is identified, many experts presume the variant is more virulent and "of concern." But whether any variant is biologically more transmissible or causes more severe illness has not been rigorously tested.
Right now, conclusions about variant transmissibility are largely based on how widespread the variant is. A variant might be deemed more contagious because it makes up a higher proportion of new infections. Delta is now the most common variant in India and Britain, accounting for more than 90 percent of new cases, and over 20 percent of new infections in the United States. Not all virologists, including us, agree that measurements like this are sufficient to declare a variant more transmissible or more contagious. What's clear is Delta may be the fitter and dominant variant for now.
To determine increased transmissibility, the ability of the virus to be passed on from one person to another, requires more than measuring infection rates. It may require experiments in people, which are unethical to conduct.
Changes in people's activities contribute to the rise of infections - such as travel, failure to mask and to adhere to physical distancing policies, and most important right now, insufficient vaccination - and these are often not considered in public discussion of variants.
The huge infection numbers in India, Nigeria and other places are not necessarily due to a particular variant, but in large part due to breached containment measures and crowded populations with poor public health infrastructures. If people are in situations in which they can be infected with the coronavirus, it's highly likely they will be infected with the fittest variant in the area. Right now, in many places, that's Delta.
What's important to understand is that people infected with the variants do not necessarily develop more severe disease or die more frequently from the coronavirus, and it is essential to get vaccinated.
The coronavirus vaccines that have been developed are very effective in preventing severe disease and death caused by all variants, including Delta. Vaccines might not always prevent infections, but they make a substantial impact in reducing virus spread and risk for serious health problems. People who are unvaccinated are at a great risk for infection and harm from any variant of the coronavirus.
During a pandemic, a time of unknowns, people want immediate answers to the question, what does this mutation mean? Providing the correct answers may require years of research. For now, there's little evidence that the virus is on an endless trajectory of increased transmission and virulence. Today's vaccines can still end this pandemic.
