People with Delta Variant Can Transmit Virus 2 Days Before Having Symptoms

This change could be a key feature driving the most recent surge in COVID-19 cases, a new studyTrusted Source 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.