Thus, you might be less likely to infect someone else if you were vaccinated.

Experts say that vaccination still makes it less likely that you'll catch Covid-19 in the first place -- but for those who do, new data suggests that Delta causes similar viral loads in both vaccinated and unvaccinated people.

The data is based on an outbreak investigation in Massachusetts in which nearly three-quarters of infected people had been fully vaccinated.

Sanjay Gupta.

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.

For example, the immune systems of vaccinated people includes a number of moving parts that might impact how much they are able to spread it.

Walensky said that ongoing outbreak investigations will help uncover more about what happens when these breakthrough infections do occur.

"We are now continuing to follow those clusters to understand the impact of forward transmission of those vaccinated people," she said earlier this week.

"But again, I want to reiterate, we believe the vast majority of transmission is occurring in unvaccinated people and through unvaccinated people."

Vaccination is the best tool against Delta

The effectiveness of Covid-19 vaccines is a spectrum: As you move from asymptomatic infection to hospitalization and death, effectiveness eventually reaches over 90%.

CDC documents estimate that vaccines reduce the risk of infection three-fold, and the risk of severe disease or death 10-fold or greater.

"Getting vaccinated continues to prevent severe illness, hospitalization and death -- even with Delta," Walensky said this week.