- Dr. Anthony Fauci said it would be "reasonable" to assume vaccinated people are less likely to spread COVID-19.
- Vaccinated people who get COVID-19 typically have less virus in their nasal passages.
- That would suggest that breakthrough infections are less contagious than infections in unvaccinated people.
- See more stories on Insider's business page.
Fully vaccinated people who get "breakthrough" cases of COVID-19 are probably less likely to spread the virus to others, Dr. Anthony Fauci said in a White House briefing today.
When asked if breakthrough cases are contributing to the spread of coronavirus in the US, the nation's top infectious disease expert said it would be "a reasonable assumption" to say vaccinated people who contract COVID-19 are less likely to transmit it compared to unvaccinated people.
Fauci said vaccinated people who develop asymptomatic infections have "considerably less" virus in their nasal passages compared to unvaccinated people with asymptomatic infections.
"I think one can make a reasonable assumption, based on the level of virus in the nasopharynx, that it would be less likely that that vaccinated breakthrough person would transmit compared to an unvaccinated person," Fauci said in the briefing.
Mild cases may have a smaller transmission window
Fauci's theory may soon be backed up with real-world data. He mentioned a large ongoing study that is currently tracking transmission in vaccinated and unvaccinated people.
Will Lee, the vice president of science at Helix, a testing company helping the CDC track variants, previously told Insider that areas with higher vaccination rates tend to have fewer cases of COVID-19, even with the Delta variant going around.
Studies in the US and the UK have indicated that Delta cases are typically milder in vaccinated people. This means they're likely to be infectious for a shorter period of time, narrowing the transmission window, Lee said.
Additionally, studies from Israel have confirmed that people who get COVID-19 despite being fully vaccinated typically have much less virus in their systems, as Fauci said. The findings haven't yet been peer-reviewed, but they add to the growing evidence that vaccinated people are less likely to transmit the coronavirus.
With the Delta variant - "a formidable variant," according to Fauci - circulating worldwide, vaccination is at the very least a powerful tool for avoiding hospitalization, and it may turn out to help curb transmissions as well.