Experts say that vaccination makes it less likely that you'll catch Covid-19 in the first place -- but for those who do, this data suggests they could have a similar tendency to spread it as unvaccinated folks.

"High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with Delta can transmit the virus," Dr.

Genetically sequenced cases revealed the Delta variant as the main culprit.

The researchers found evidence that viral loads were similar among 127 fully vaccinated people and 84 others who were unvaccinated, partially vaccinated or whose vaccination status was unknown.

The finding that the Delta variant resulted in similar viral loads "was a pivotal discovery leading to CDC's updated mask recommendation," Walensky said Friday.

Not only did vaccinated people tend to have lower viral loads, but they also had milder symptoms and were sick for less time.

But research has shown that Delta spreads more aggressively.

Measles, chickenpox, this -- they're all up there," Walensky told CNN late Thursday.

The CDC document also cited reports indicating the variant might cause more severe disease, as well.

But even with similar viral loads, it's not a foregone conclusion that vaccinated people are necessarily as contagious as unvaccinated people.

"This is intriguing data, it's important, but I'm not positive that you're equally as infectious if you're vaccinated," said Dr.