The Delta Variant & the Vaccinated: One Expert's Take on the Data

News that the highly contagious Delta variant of COVID-19 can be picked up and spread by vaccinated folks has sparked confusion and concern, and an infectious disease expert wants to clarify.

These worries follow a recent U.S. Centers for Disease Control and Prevention recommendation that urged even vaccinated folks to wear masks indoors in areas with substantial or high rates of COVID-19 transmission.

The advisory came soon after a July 4th COVID-19 outbreak in Provincetown, Mass., in which three-quarters of people who got infected were fully vaccinated.

The finding — detailed in a CDC report — suggested that even vaccinated people could spread the virus between each other.

However, Dr. Adam Lauring, an infectious disease specialist at Michigan Medicine-University of Michigan, is telling people to not to read too much into that one case.

"While this is clearly something to pay attention to, in the CDC report, they are pretty clear in the discussion about the limitations and what they are saying and not saying," Lauring said in a university news release. "Of course, not everyone [reading the advisory] made it that far."

For example, he said, as more people get their shots, of course more 'breakthrough' cases will be detected in the ever-growing number of people who are vaccinated.

As well, a nasal swab COVID-19 test can measure how much viral RNA is present in a person's nose -- but not how much of that virus is infectious.

"The amount of genome present is a marker, but it is not the same thing as saying these people are equally as infectious," Lauring said.

Also, a swab is taken at one moment in time, so it can't confirm how long someone is infectious.

"You could picture a situation where vaccinated people with Delta have a really steep rise and then a really steep fall in the amount of virus shed, whereas an unvaccinated person would have a steep rise that would remain high for longer," Lauring said.

While a majority of infections will be in unvaccinated people, the big change is that it now appears that vaccinated folks with the Delta variant will transmit the virus more often than with other variants.

That means additional measures — like wearing masks in certain situations, such as indoor spaces in areas where case levels are high — will be required in addition to vaccines to stop the spread of COVID-19.

Early data show the vaccines are more than 80% effective at preventing severe illness and death and are still reducing transmission.

Case counts in the United States are highest in areas with low vaccination rates — evidence that the vaccines are working against all variants, according to Lauring.

As for boosters, he said: "I'm more concerned about people who have not been vaccinated at all."

Lauring also noted that high vaccination rates are needed to protect younger children who aren't yet eligible for vaccination, as well as immunocompromised people. Vaccination is also key to reducing the emergence of even more contagious variants, he added.