What is it about the Delta variant that makes it spread so easily?

·5 min read
Garden Grove, CA - July 17: Young people wearing traditional Vietnamese outfits join thousands of Vietnamese-Americans and faithful Catholics during a Mass celebration following the Our Lady of La Vang Solemn Blessing ceremony at Christ Cathedral in Garden Grove Saturday, July 17, 2021. The new $12.6 million shrine, with a centerpiece showing Our Lady of La Vang statue, the first large-scale rendition in the U.S. of a figure sacred to Vietnamese Catholics. Mass was celebrated following the blessing. The unveiling a new shrine serves as a testament to the remarkable journey of the Vietnamese-American people who survived war and religious persecution and emerged and regrouped in a new reality where they have flourished in faith and community. The centerpiece of the Our Lady of La Vang Shrine is a statue of the Virgin Mary as she is believed to have appeared before a group of persecuted Vietnamese Catholics in 1798. During that historic Marian apparition, which took place in a remote rainforest region in Vietnam, the Blessed Mother offered the desperate parishioners hope and guidance. In the centuries since, Our Lady of La Vang, as the apparition has since been named, has represented hope, faith and promise to Vietnamese Catholics around the world. "This shrine to Our Lady of La Vang is not only another example of how beauty draws to God, but it is a testimony to the faith of our Vietnamese brothers and sisters who have contributed so much to the life of our parishes here in Orange County, and which then points us all to the Mother of God and her protection," said Bishop Kevin Vann. The shrine represents both that historic apparition and honors the important contributions of the Vietnamese-Catholic diaspora in Orange County, which is home to the world's largest population of Vietnamese outside of Vietnam. An estimated 100,000 Vietnamese Catholics live in OC. Standing on a cloud, Mary is depicted wearing a traditional Vietnamese ao dai dress and khan dong hat. She has a Eurasian face and holds the Baby Jesus. Behind her are three supporting poles that hold up the canopy-like structure, which itself symoolizes the rainforest setting of the 1798 Marian apparition. The poles resemble the three banyan trees that were behind the Virgin Mary during the apparition. The shrine also contains donor names and the names of 117 Catholics who were martyred for their religious beliefs in Vietnam. The names detail how and when each person died. The statue, which weighs an estimated 16,000 pounds and is 12-feet-tall statue, was carved from white marble extracted from a quarry in Carrara, Italy. (Allen J. Schaben / Los Angeles Times)
Young people at a Mass celebration at Christ Cathedral in Garden Grove wear face masks to protect themselves and others as the Delta variant spreads. (Allen J. Schaben/Los Angeles Times)

The Delta variant continues to tear across the United States, causing hospital rates to soar and leading the Centers for Disease Control and Prevention to recommend that even people who are fully vaccinated resume wearing masks in indoor public spaces in most parts of the country.

The Delta variant was first detected in India in December of 2020 and likely arrived in the United States around March. It wasted little time outcompeting all other variants here to become the country's dominant coronavirus strain. The CDC estimates that Delta is responsible for about 82% of recent SARS-CoV-2 infections here.

“The virus has been very successful in humans from Day One, but this Delta variant just puts the earlier variants to shame,” said Michael Worobey, a virologist at the University of Arizona.

Luckily for us, the Delta variant is far less likely to cause serious disease or death in people who are fully vaccinated against COVID-19. However, the variant does have a formidable super power: It replicates far more rapidly and efficiently in the human body than any previous known variant.

Nasal swabs reveal that people infected with Delta have 1,000 times more virus particles in their upper respiratory systems than those who were infected with the coronavirus that sparked the pandemic in the first place.

“That means every cough, every sneeze is packed with that much more virus,” said Dr. Jaimie Meyer, an infectious disease physician at Yale Medicine in New Haven, Conn.

Worobey put it this way: “If you think of the individual particles as machine gun fire, the Delta variant is shooting at us at 1,000 rounds per second, while previous variants were only shooting at one round per second.”

This helps explain why Delta is roughly twice as transmissible as the original strain of the virus.

Delta's rapid, efficient replication also helps explain another troubling aspect of this supercharged foe: A person infected with this variant can pass it along sooner than a person who harbors another strain.

With previous variants, it took about six days after an initial infection for an individual to produce enough virus to infect others, said Chunhuei Chi, director of the Center for Global Health at Oregon State University.

The Delta variant reduced that timeline to just four days, allowing it to spread through communities with unprecedented speed.

“Delta is different,” said Dr. Joseph Kanter, state health officer of the Louisiana Department of Health. “The transmission dynamics are different. The level of viral load we see in people is different.”

Scientists are still analyzing exactly what mutations in the Delta variant’s genome helped it outcompete earlier versions of SARS-CoV-2.

“It’s a very good question,” Worobey said. “It could be a variety of things.”

One candidate is a mutation in the virus’ spike protein that improves its odds of entering a target cell.

Viruses cannot replicate on their own. Instead, they must hijack the machinery of a host cell to make copies of themselves. Those copies are then released into the body and infect other cells, repeating the cycle.

Like other versions of SARS CoV-2, the Delta variant has to first bind to a protein on the surface of the cell it plans to infect. Then it has to cleave itself at the exact right time and place to force itself inside.

Researchers have found evidence that one of the Delta variant’s mutations — called P681R — makes this essential cleaving step easier and more efficient than it is in previous variants.

This may sound like a subtle change, but the cumulative effect of a mutation that improves the odds of the virus entering a cell is significant, said Benhur Lee, a microbiologist at the Icahn School of Medicine at Mount Sinai in New York.

“Multiply this by a gazillion times and average it out, and what you might see is increased transmissibility,” he said.

There may be additional forces at work too, he said, since Delta's genome has other mutations that don't affect the spike protein.

“We do not know that the spike is the answer to everything,” Lee said.

Other possibilities include genetic changes that allow individual virus particles to bind more easily — and hold on longer — to the surface of cells in our nasal passages and upper airways, and those that may make it more difficult for the immune system to fend off viral invaders.

One thing Lee can say for sure is that the Delta variant's increased transmissibility has nothing to do with how far individual virus particles can travel, or how long they can remain in the air.

“It is not the case that something magic happened such that the virus is more airborne,” he said.

With all this in mind, what is the best way to protect yourself from Delta?

The answer from scientists will sound familiar: Get vaccinated, wear a mask, and avoid crowded, poorly ventilated areas.

And, yes, even vaccinated people should wear masks in public indoor spaces because with the Delta variant boosting viral loads, breakthrough cases are more likely.

“As a general rule, what would have been an unsuccessful encounter with the virus is now much more likely to be successful,” Worobey said. “That’s why we need to be thinking not just vaccines as protection against this, but back to the mask-wearing we had hoped to put behind us.”

Still, it's worth keeping in mind that vaccines continue to provide an amazingly effective line of defense. In Los Angeles County, for example, unvaccinated residents still accounted for almost three times as many infections, even though they’ve been a minority of the population since the start of the month, according to data released by the County's Public Health Department. In addition, 92% of all hospitalizations occurred in people who weren't vaccinated.

“The main advice I would give is to get vaccinated,” Lee said.

This story originally appeared in Los Angeles Times.