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The Delta variant has taken over the U.S. in the last few weeks, increasing COVID cases, hospitalizations, and deaths once again. The fast-spreading variant is so concerning that the Centers for Disease Control and Prevention (CDC) just reversed mask recommendations for vaccinated people in areas where the virus is surging on July 27. Despite the new mask guidance and increased reports of breakthrough infections, CDC director Rochelle Walensky, MD, maintains that the new strain is mainly affecting unvaccinated individuals. But whether vaccinated or not, the CDC has found some worrying similarities among people who get sick with the Delta variant.
On July 27, CDC officials held a press briefing where they announced the agency's updated mask guidance and discussed the virus' spread with the now-dominant Delta variant. According to the CDC's data, 8 in 10 sequenced COVID cases are infected with Delta, as of right now—and that's concerning, because the variant has notable differences compared to previously dominant strains.
"I have seen new scientific data from recent outbreak investigations showing that the Delta variant behaves uniquely differently from past strains of the virus that cause COVID-19," Walensky said during the briefing.
One of the major changes is that everyone infected with the Delta variant "may be contagious and spread the virus to others," whether unvaccinated or vaccinated, per the CDC. Walensky says this new scientific data has emerged from recent Delta variant outbreaks in several states and other countries. "This new science is worrisome and unfortunately warrants an update to our recommendations," she said.
According to the CDC, both vaccinated and unvaccinated people with COVID have a similar amount of virus in their bodies. When the Alpha variant was dominant, health experts believed that vaccinated individuals had reduced viral loads and could not transmit the virus to others. However, Walensky says that vaccinated people infected with the Delta variant could spread the virus further.
"We felt it important for [vaccinated] people to understand that they have the potential to transmit virus to others," Walensky said. "And that is important in the case, for example, of a vaccinated individual who might be going to visit an immunocompromised family member. We wanted to make sure that they took the precautions necessary to not pass the virus to them."
Walensky said the rate of transmission among vaccinated individuals is still low because breakthrough infections are rare. According to ABC News, an unpublished internal CDC document obtained by the news outlet showed that around 153,000 symptomatic breakthrough cases have occurred as of last week out of more than 156 million fully vaccinated U.S. adults. This is only .098 percent of vaccinated people, though it doesn't include asymptomatic breakthrough infections and breakthrough cases among adolescents.
"Vaccinated individuals continue to represent a very small amount of transmission occurring around the country," Walensky confirmed during the press briefing. "Of the transmission that is happening in the country right now, the vast majority of transmission occurring is occurring through unvaccinated individuals."
The CDC also estimates that the risk of symptomatic breakthrough infection with the Delta variant is reduced by seven-fold through the vaccines. And the reduction for hospitalizations and deaths is even higher, at 20-fold. "We continue to strongly encourage everyone to get vaccinated. Getting vaccinated continues to prevent severe illness, hospitalization, and death, even with Delta," Walensky said.