'It's Incredibly Contagious': The COVID Delta Variant Is Strong, Local Doctors Say A Vaccine Is The Best Defense

CHICAGO (CBS) -- There's new information now about the Delta variant.

The CDC warning it is as contagious as the chicken pox and more transmissible than the common cold.

For the first time, the CDC is sharing what it learned about a recent outbreak at a popular East Coast tourist spot, including a large number of breakthrough cases.

CBS 2's Lauren Victory took questions and concerns to one of Chicago's top doctors.

Jeff Fest just got underway with live music, another sign of normalcy for a North Side community But with a study from the CDC is causing some chatter.

What should you know before coming out to have a good time?

"The truth is that it's incredibly contagious," said. Dr. Emily Landon, Chief Epidemiologist for the University of Chicago who wanted to set the record straight before anxiety consumes you.

CBS 2 tapped Dr. Landon to decipher just-released statistics from the Centers for Disease Control and Prevention.

The CDC study linked hundreds of COVID-19 cases to large public gatherings in Massachusetts. Seventy-four percent of those cases were in fully vaccinated people.

Let that sink in but don't let that scare you.

"We have to remember that the vaccine is not perfect, no vaccines are," said Dr. Landon who went on to explain what likely happened on the East Coast.

"We know that the vaccination rate in this particular place was very, very high. The higher the vaccination rate in the community, the more likely you'll see cases in vaccinated individuals, because the only individuals to get sick are vaccinated individuals," said Dr. Landon.

Of the nearly 500 people sickened, only five were hospitalized and none died. Those numbers used to be much worse before vaccines.

"Instead of seeing 1% of people die and 15% of people hospitalized. We see like 15% of people getting sick and only 1% of them end up in the hospital and none of them dying. So let's look at this as a big success for vaccines in this case," said Dr. Landon.

If you are one of the unlucky ones – vaccine double dosed but virus diagnosed, Dr. Landon says your symptoms will likely be similar to that of a nuisance cold.

Still, a nuisance cold could cause damage to an older person or someone immunocompromised.

The Cook County Department of Public Health is hoping to contain the spread of the Delta variant by announcing a new mask advisory this week. Everyone older than the age of 2, vaccinated or not, is asked to wear a mask indoors.

But if the new strain of COVID is so contagious, why not require masks indoors again? There are legal hurdles explains Dr. Rachel Rubin from CCDPH and enforcement is tricky.

She argues issuing a strong advisory about masks instead is easier and will help take the guesswork out of who is vaccinated and who is not.

"This way you can just say, [because of the advisory] I'm not letting you into my store. I'm not letting you into my restaurant unless you remain masked," said Dr. Rubin.

Late Friday, the city of Chicago became the latest to recommend that everyone over the age of two wear a mask indoors even if vaccinated.