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With the coronavirus Delta variant, people can transmit the virus for almost 2 full days without feeling any symptoms. Jeff Bergen/Getty Images
  • According to a new study from the journal Nature, people with the Delta variant can transmit the virus for almost 2 days before experiencing any symptoms.
  • Presymptomatic transmission may account for nearly 75 percent of Delta variant infections.
  • Vaccinated people with rare “breakthrough” infections may also be able to transmit the virus as easily as unvaccinated people because of elevated viral loads.
  • Experts contend that vaccines remain our best available tools to control the spread of COVID-19 and protect people from serious disease, hospitalization, and death.

People with the Delta variant of the coronavirus may be able to transmit the virus for nearly 2 days before having symptoms.

This change could be a key feature driving the most recent surge in COVID-19 cases, a new study in the journal Nature suggests.

Presymptomatic transmission was a feature of previous coronavirus variants, but the research suggests the gap between receiving a positive test to feeling systems was just 0.8 days. With the Delta variant, it’s 1.8 days.

As a result, nearly three-quarters of infections with Delta happen during the presymptomatic phase, the research suggests.

“The Delta strain is more contagious, in part, because infected individuals carry and shed more virus than previous versions,” said Dr. Stefen Ammon, medical director of the COVID-19 Task Force for DispatchHealth, an on-demand healthcare service.

“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,” he added.

Because of this increased transmissibility, Delta has become the dominant variant worldwide. It accounts for more than 90 percent of COVID-19 cases in the United States.

And while vaccines are still extremely effective at preventing hospitalization and death from COVID-19, studies are showing that vaccinated people who contract the coronavirus, so-called “breakthrough infections,” may have viral loads as high as those among unvaccinated individuals, meaning they can transmit the infection.

This differs from our previous understanding of COVID-19 vaccine effectiveness.

“When COVID-19 vaccines first became available, they demonstrated a great ability to prevent the recipient from contracting any form of COVID-19, which largely removed vaccinated asymptomatic and presymptomatic exposures from the equation,” Ammon told Healthline.

“However, the Delta variant has developed an ability in some instances to partially evade the immunity provided by vaccination, meaning there are more breakthrough infections in vaccinated individuals from the Delta variant than were seen from previous versions of the virus,” he said.

But it’s not all bad news.

Recent studies show the critical importance of getting the COVID-19 vaccine both for personal health and limited transmission.

“The fact that asymptomatic people spread the virus is not new information. We have known that people are contagious before they are symptomatic for over a year,” said Dr. Jason Gallagher, an infectious disease expert and clinical pharmacy specialist in infectious diseases at Temple University Hospital in Philadelphia.

“However, we are learning more about this finding very quickly. Two studies now show that the viral RNA declines more quickly in vaccinated people than unvaccinated people, suggesting that they are less likely to transmit virus to others,” he said.

These accumulated findings, along with the rapid rise in COVID-19 case numbers nationwide while vaccination rates have lagged, have brought back public health advisories from earlier in the pandemic.

These include mask mandates, calls for physical distancing, and one newer wrinkle — vaccination mandates — in many cities and states.

“All people, both vaccinated and unvaccinated, should wear masks while inside in public or crowded spaces,” said Dr. Elizabeth Beatriz, an epidemiologist at the Massachusetts Department of Public Health in the Bureau of Community Health and Prevention and a public health and COVID-19 adviser at Parenting Pod.

“This is particularly true if you are in an area where there are a lot of COVID infections, or you live with someone who is unvaccinated, including children, or someone who is immunocompromised, or who is likely to get very sick if they do become infected with COVID,” she said.

“Even though there has been a lot in the news about ‘breakthrough infections’ among the vaccinated, we continue to see that those who are not vaccinated are the ones getting very sick, being hospitalized, and dying,” Beatriz said.

“To protect yourself, vaccination is key.”