Why some variants of the coronavirus are more contagious – and how we can prevent them

After a year of isolation, canceled events and virtual meetings, the pandemic’s fatigue is setting in. But even as more people drop their guard and allow security measures to subside, a crop of SARS-CoV-2 variants is spreading rapidly. through populations around the world. The rapid rise of a trio of mutant viruses indicates an increase in transmissibility, accelerating the virus’s leaps from one host to another.

Scientists are now racing to decipher exactly how the confusion of mutations in each variant influences viral spread. This research is vital to understand the risks of current strains and to predict how future variants may change the course of the pandemic.

“We have uncontrolled viral spread across much of the world,” says Adam Lauring, an infectious disease physician and virologist at the University of Michigan. “Therefore, the virus has many opportunities to evolve.”

More cases mean more deaths and more people who suffer lasting impacts from attacks with COVID-19 – but not all news is sad and reprehensible. On the one hand, the latest analyzes of vaccines suggest that they remain effective against the new variants. And until people are vaccinated, the same measures already known to prevent infection – such as masking, detachment, hand washing, ventilation and spending time outdoors – become even more important to contain the viral tide.

“The variants may be more transmissible, but the physics have not changed,” says Müge Çevik, an infectious disease physician at the University of St. Andrews in Scotland.

A virus replicates itself by hijacking its host’s cellular machinery to make copies of itself. But, like a person who makes mistakes when typing the same phrase over and over, genetic copies accumulate small errors or mutations. Many changes do not affect the function of the virus and some even impair the ability to multiply SARS-CoV-2, but they continue to happen. “Viruses are mutated; that’s what they do, ”says Akiko Iwasaki, an immunologist at the Yale School of Medicine in Connecticut.

Sometimes, neutral mutations are transmitted at random and can become common in a population. But changes that are beneficial to the virus can also boost its spread, leading to a variant that outperforms other local varieties and can increase the number of cases.

This appears to have happened in the United Kingdom, Brazil and South Africa. In the United Kingdom, variant B.1.1.7 probably boosted the record peak of COVID-19 cases in the region in January. The variant is now circulating in more than 60 countries, including the United States – and projections suggest it will become the most common virus strain in the United States in mid-March.

An independent strain called P.1 may also be causing a wave of cases in Manaus, Brazil, where it was responsible for almost half of the new COVID-19 infections in December. On Tuesday, Minnesota officials reported the first American case of P.1 in a resident who had previously traveled to Brazil. And a third strain generating alarms, known as B.1.351, was first identified amid a wave of infections in December in South Africa.

But exactly how the mutations gave the variants an advantage remains uncertain. A specific mutation, known as N501Y, appeared independently in all three variants, suggesting that it could provide an advantage for the virus. “This is a sign that there is natural selection going on,” says Lauring.

The N501Y mutation affects the virus’s spike protein, which is the key it uses to unblock entry into the host’s cells. Laboratory experiments suggest that this mutation improves the spike protein’s ability to bind to cells, suggesting that it may increase the ability of variants to infect hosts.

Another possibility is that new variants will make infected people harbor more copies of the virus. This results in more viral “spillage” in droplets in the air expelled when people speak, sing, cough and breathe. But different studies have produced conflicting results, and the largest study on the subject suggests that the new variants are unlikely to increase viral load, says Çevik. The discrepancy may come from the time of the studies, she adds, since previous research suggests that viral loads increase as infections in the community increase.

Mutations can also help viruses like SARS-CoV-2 to spread in many other ways. Some can make sick people contagious for long periods of time, for example. Other changes can help viruses survive longer outside the body or even increase their ability to replicate. And to complicate matters, individual adjustments to the virus genome may work differently on their own than as a patchwork of mutations.

Scientists are also intriguing with another crucial question: exactly how much more contagious are the new variants of the coronavirus? As evidence for the movement of B.1.1.7 across the population increases, a recent model suggests that it is 56% more transmissible than previous forms of the virus – but these are difficult to determine.

Without routine screening, many SARS-CoV-2 infections still escape the radar, says Ellie Murray, assistant professor of epidemiology at the Boston University School of Public Health in Massachusetts. This makes it difficult to get an accurate picture of what is going on. Our own human complexities also present a challenge, such as differences in susceptibility between people.

“In general, when you’re talking about complicated and confused human beings who live their normal lives – or at least their normal COVID lives – it’s really difficult to put an exact number to increase transmissibility, especially when you’re looking at it in real time , ”Says Angela Rasmussen, virologist at the Georgetown Center for Global Health Science and Security in Washington, DC

Scientists are less certain about the increased transmissibility of variants found for the first time in Brazil and South Africa. While the P.1 strain was running through Manaus, more than 70% of the local population had already been infected with previous versions of the virus , which was theoretically tall enough to achieve herd immunity. But then the cases arose, raising concerns that the variant could bypass the immune defenses of people who had been previously infected.

Similar concerns have been raised about the variant initially found in South Africa, which shares some mutations with P.1. A modeling effort suggests that the spread of 501Y.V2 can be explained by an increase in transmissibility of about 50 percent. But as an alternative, it may be the result of 501Y.V2 escaping immunity in 21 percent of people previously infected – and it is possible that the two mechanisms work together.

“It’s really hard to know who is which,” says Penny Moore, a virologist at the National Institute of Communicable Diseases and the University of Witwatersrand in South Africa.

Moore and colleagues used “pseudoviruses” that infect cells using the same proteins as SARS-CoV-2, but are not capable of replication, to study the possibility of the virus evading our immune system. Their results suggest that mutations in 501Y.V2 may decrease the effectiveness of antibodies in the blood of people previously infected with the virus. But understanding whether this could lead to more reinfections, or if it could affect the vaccine’s effectiveness, will require further studies, she says.

“What we don’t know yet – nobody knows it – is how much antibody is enough to protect people from infection,” says Moore. “What we need are human clinical trials to really answer whether that reduces the vaccine’s effectiveness.”

The increase in variants emphasizes the need for greater precautions against the virus, particularly as the vaccine’s release remains slow. Tests, masks and social detachment will help stem viral spread. And as people get tired of isolation, Çevik emphasizes that these measures need to be employed intelligently, allowing for activities where the risk is low, like outdoors.

In enclosed spaces – including the small huts now commonly used for al fresco dining, Murray says – the virus has a greater chance of forming in the air and infecting people with COVID-19. Contact screening showed that the risk of viral transmission indoors is 20 times greater than outdoors. While there is still some risk on the outside, it is extremely low for brief contact between people, says Çevik.

“We need to look at risk on a spectrum,” she says, and think more about when we will let our guard down. “I think people worry about strangers outdoors, but they forget everything when they have dinner with friends.”

Many researchers are also pushing for better face masks. Although they are not a panacea and should be combined with other measures such as social detachment, masks can help contain viral spread when people need to enter high-risk areas. Abraar Karan, an internal medicine doctor at Harvard Medical School’s Brigham and Women’s Hospital in Massachusetts, has advocated the dramatic increase in the production of high-filtration masks for the general public. “We are at war with this virus,” he says. “It’s not a joke.”

Experts also emphasize that government support is critical in efforts to stop transmission. People need resources to securely isolate – quarantine sites and financial support to avoid work in the event of illness. And streamlining vaccinations is vital, as it will eliminate the virus’s opportunities to replicate and evolve. “The faster we can vaccinate people, the less likely it is that more of these variants will appear,” says Iwasaki.

Some help may be on the way in the U.S., as President Joe Biden works to approve his government’s $ 1.9 trillion plan to combat the pandemic. Even so, people will need to work together to remain vigilant and slow the spread of the virus.

“This is not forever; this is not necessarily even in the next six months, ”says Rasmussen. But “now, the immediate future is no time to relax”.