News headlines and health experts on social media are sounding the alarm bells for yet another variant of the coronavirus, this time Delta, claiming it is far more contagious and possibly deadlier than any another variant seen so far. It’s easy to see why: New variants of the virus continue to emerge and cases are on the rise in many countries. But it’s still unclear whether the new variants pose a unique or substantial risk, and as virologists we are concerned that the misunderstandings and the risk they pose could cause confusion and panic.
As the coronavirus spread globally, its genome has changed – mutated – as expected for any virus. These mutations can affect the “physical form” of the virus, its ability to reproduce and spread. Some mutations weaken a virus, others have no measurable effect, and others make it stronger.
As a virus gets fitter, it will outperform less fit viruses – and Delta isn’t the first variant to beat its predecessors and competitors in some areas. There is the Alpha variant which has become dominant in Britain and the Gamma variant which has become dominant in Brazil. Such changes are not unique to the coronavirus. An increased viral form occurs during each flu season, which is why some flu variants may circulate more widely than others.
Just because one variant replaces another does not necessarily mean that it is more contagious or more deadly to people who are infected with it. As it has been for the past year and a half, human behavior is far more important than any variant in shaping the course of the pandemic.
A virus can mutate in several ways to increase its physical form. While much has been focused on changes in the peak proteins of the virus, which allow the coronavirus to invade cells, a virus can also maintain changes in other proteins. Such changes can allow the virus to replicate more easily or escape the immune system, for example. They can even allow the virus to persist longer in the nasal passages.
Questions around the Covid-19 vaccine and its deployment.
Determining the impact of a given mutation requires extensive laboratory research. Sometimes the first conclusions about a particular mutation can be incorrect. When the first notable variant, D614G, appeared last winter, some scientists believed that changes to the virus’s spike protein made the virus more contagious. But subsequent research has shown that this is not the case. Even so, whenever a new change in the spike protein is identified, many experts assume that the variant is more virulent and “of concern.” But whether a variant is more biologically transmissible or causes more serious disease has not been rigorously tested.
At present, conclusions about the transmissibility of variants are largely based on the extent of the variant. A variant could be considered more contagious because it represents a higher proportion of new infections. Delta is now the most common variant in India and Britain, accounting for over 90% of new cases and over 20% of new infections in the United States. Not all virologists, including us, agree that such measures are enough to declare a variant more transmissible or more contagious. What is clear is that Delta may be the fittest and most dominant variant right now.
To determine increased transmissibility, the ability of the virus to spread from person to person requires more than measuring infection rates. It may require experiments on people, which is unethical.
Changes in people’s activities are contributing to the increase in infections – such as travel, non-masking and disregarding physical distancing policies, and most importantly at this time, insufficient vaccination – and those- these are often not taken into account in the public debate on variants.
The huge numbers of infections in India, Nigeria and other places are not necessarily due to any particular variant, but in large part to unfulfilled containment measures and overcrowded populations with poor public health infrastructure . If people are in situations where they can be infected with the coronavirus, it is highly likely that they will be infected with the most suitable variant in the region. Right now, in many places, it’s Delta.
What’s important to understand is that people infected with the variants don’t necessarily develop more serious illness or die from the coronavirus more frequently, and getting vaccinated is essential.
The coronavirus vaccines that have been developed are very effective in preventing serious illness and death caused by all variants, including Delta. Vaccines may not always prevent infections, but they have a substantial impact on reducing the spread of the virus and reducing the risk of serious health problems. Unvaccinated people are at great risk of infection and damage 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 can take years of research. As of yet, there is little evidence that the virus is on an endless trajectory of increased transmission and virulence. Today’s vaccines can still end this pandemic.
Amy B. Rosenfeld and Vincent R. Racaniello is a virologist in the Department of Microbiology and Immunology, College of Physicians and Surgeons, Columbia Vagelos University. Dr. Rosenfeld has studied viruses in the laboratory for two decades. Dr Racaniello is co-author of the Principles of Virology manual and host of the podcast “This Week in Virology” (“TWiV”).
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