74 Percent of Delta Variant Infections Have This in Common, New Study Says

A new study found the majority of Delta variant COVID-19 infections occur in this situation.

In the last few months, the Delta variant has proven to be a more virulent and contagious version of the COVID-19 virus than anything that's come before it. Scientists continue to study the variant to figure out what makes it so much more transmissible and deadly, but a new report published in the journal Nature has found that three-quarters of infections caused by the Delta variant have one thing in common that proves it's spreading in a different and more powerful way than previous strains of COVID-19.

Nature looked at a pre-print of a study out of the University of Hong Kong, which has not yet been peer-reviewed. The university's head of the Division of Epidemiology and Biostatistics, Benjamin Cowling, PhD, and his fellow researchers studied data from 101 people in Guandong, China, who'd been infected with the Delta variant in May and June. The researchers were interested in determining how COVID infections caused by the Delta variant spread from those individuals to their close relatives and friends and how those infections differed from earlier variant transmissions.

RELATED: If You Got This Vaccine, You May Be More Protected Against Delta.

The study found that there was typically a 1.8-day gap between people testing positive for COVID-19 caused by the Delta variant and the onset of symptoms, which is more than twice as long as for other COVID-19 variants. For those who contracted the previously dominant Alpha variant of the virus, for example, the time between testing positive and showing symptoms was just .8 days.

Researchers found that a staggering 74 percent of all COVID-19 Delta variant transmissions happened in the two-day window before infected patients began feeling symptoms. That longer window, in effect, means a greater chance that someone will spread the virus to another person during their presymptomatic phase because they don't know they're sick.

"While the earlier version of COVID-19 was as transmissible as the common cold, the Delta variant is more transmissible than seasonal influenza, polio, smallpox, Ebola, and the bird flu, and is as contagious as chickenpox," Stefen Ammon, MD, the director of the COVID-19 Task Force for DispatchHealth, told Healthline.

RELATED: If You Live in These States, the Delta Surge Could Be Ending Soon.

It's clear that part of what makes the Delta variant so powerful is that people can spread the disease up to two days before they begin feeling symptoms. The longer transmission window also applies to vaccinated people who contract a breakthrough case from the Delta variant, who could be less likely to assume they are sick while still carrying high levels of the virus in their bodies.

According to an internal memo from Rochelle Walensky, MD, the director of the Centers for Disease Control (CDC), that was obtained by The New York Times at the end of July, vaccinated people with Delta variant infections "carry just as much virus in the nose and throat as unvaccinated people, and may spread it just as readily, if less often." In effect, this means that vaccinated people who contract the Delta variant may not feel sick yet can still pass the virus on to unvaccinated and otherwise immunocompromised people quite easily.

To add to this perfect storm, Cowling said, researchers have also found that people infected with the Delta variant had higher viral loads—meaning higher concentrations of viral particles—in their bodies than those infected with previous variants. One study found that Delta variant carriers had viral loads up to 1,260 times higher than people infected with other strains of the virus. "The Delta strain is more contagious, in part, because infected individuals carry and shed more virus than previous versions," Ammon told Healthline.

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Given that the Delta variant is much more contagious than previous variants, the CDC and other health organizations recommend that people continue to mask up and take up precautions, especially as the vaccination rate in the U.S. hovers around 52 percent and the Delta variant is vastly more dangerous to unvaccinated people, Anthony Fauci, MD, and other experts warn.

In fact, Fauci, the director of the National Institute of Allergy and Infectious Diseases, told Meet the Press in July that more than 99 percent of all COVID-related deaths in the U.S. in June 2021 were among unvaccinated people.

"Obviously there are going to be some people, because of the variability among people and their response to the vaccine, that you'll see some who are vaccinated and still get into trouble and get hospitalized and die," he said. "But the overwhelming proportion of people who get into trouble are the unvaccinated. Which is the reason why we say this is really entirely avoidable and preventable."

RELATED: Fully Vaccinated People Account for 1 in 4 COVID Cases Here, New CDC Report Says.

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