Of all the COVID-19 mutations being tracked since the start of the pandemic, delta is “the most transmissible of the variants identified so far,” according to the World Health Organization.

Since first being seen in India in December, the variant has piqued the concern of scientists, health organizations and government officials. That’s primarily due to its transmission rate, which is 60% more than the alpha variant. The alpha variant is currently the most common form of the virus in the United States.

That means the variant may be more easily spread, officials worry, particularly among unvaccinated and partially vaccinated populations.

“Already, the delta variant that sent Israel back into mitigation is a growing presence in Illinois,” Gov. JB Pritzker said Monday. “We expect it to dominate our cases statewide by the fall.”

Still, Chicago officials say there’s no need to change COVID-19-related policies or rules now.

During her weekly “Ask Arwady” question and answer session, Commissioner of the Chicago Department of Public Health Dr. Allison Arwady said that she takes variants very seriously. Still, she feels confidently that the city is “in a good place at this point” and that current rules do not need to be adjusted.

Let’s look at what we know about the variant — and what we don’t.

Where has the delta variant been located?

As of Friday, the delta variant has been identified in at least 85 countries, including the U.S.

The variant has been detected in Illinois, and also neighboring states, including Missouri, Wisconsin and Indiana.

Public health officials in Missouri said the variant is fueling a rise in infections there. In the last week, St. Louis Public Radio reports the number of COVID-19 cases among Missourians has increased nearly 20%. Epidemiologists estimate that the delta variant makes up around half of the variants identified in patients.

How prevalent is the delta variant in Illinois and Chicago?

Not very, right now. As of Tuesday, there have been 103 cases of COVID-19 delta variant identified in Illinois, according to the latest numbers from the Illinois Department of Public Health.

That’s up from 84 cases across the state the previous week. And last week, Dr. Arwady said there were at least 70 cases of it in the city.

But that still remains a small number, given there have been nearly 10,000 cases of various variants identified in the state so far. Given its higher rate of transmission, health officials remain wary it will grow exponentially in the coming weeks.

How is the variant detected?

Testing for variants is different from testing for whether or not an individual has COVID-19. If an individual has their nose swabbed to test whether they have COVID-19, that test will not reveal if their infection was caused by a variant.

Instead, a different, highly specialized test is necessary — work that is being done on samples of confirmed COVID-19 cases across the country. It’s called genomic surveillance, and it allows scientists to determine which strain of COVID-19 may be circulating and how quickly it’s spreading.

In Chicago, Rush University Medical Center is one of the partners testing for variants. The city is paying the university $3.5 million to run the testing.

Is the delta variant more dangerous?

The jury is still out on whether the delta virus makes people sicker, Dr. Arwady said.

“Locally, we’ve detected many cases of this delta variant,” she said. “We have seen it spread. We have not seen it be particularly more likely to have somebody be hospitalized.”

Other media have also reported there is no evidence, yet, that the delta variant makes people more sick than other variants.

Should I worry about the delta variant if I’m vaccinated?

The delta variant is far less of a concern for those who are vaccinated. If you are fully vaccinated, meaning two weeks have passed since your second dose, NPR reports citing various doctors and studies that “odds are highly favorable that you won’t get a breakthrough COVID-19 infection, and even better that if you are one of the unfortunate few, you won’t get a severe case.”

Dr. Arwady said that this holds true for those who received the single shot vaccination from Johnson & Johnson as well.

“Across all types of variants here in Chicago, since the vaccine was fully available, 98% of our deaths, 97% of our hospitalizations have been of people who are not fully vaccinated and that has been holding, even for the delta variant,” Dr. Arwady said.

The concern is for those who are unvaccinated. Dr. Arwady said that in neighborhoods or social networks in which people are unvaccinated, even a single case of the delta variant is more likely to cause people to get sick.

The most important thing is to get vaccinated, she says.

Does this mean I need to wear a mask in public?

The WHO recently recommended that fully-vaccinated people continue to wear masks.

However, Dr. Arwady said that WHO made that recommendation broadly as vaccines are not widely available throughout the world. But, they are widely available in Chicago.

As of now, the city is sticking with the Centers for Disease Control and Prevention’s guidance and will not adjust its mask policy. Those who are fully vaccinated in Chicago do not need to wear masks, including indoors.

“Right now, while our outbreak remains in very good control locally, even with the delta here, there’s not a reason to adjust that guidance,” Arwady said.

Arwady noted that if you are fully vaccinated but immunocompromised, if you have young children or if you are worried about unvaccinated people in your social circle, then you may want to choose to wear a mask.

Still, Dr. Arwady said that she won’t rule out that mask mandates indoors could return — depending on changes in case numbers due to the variant.

Correction: A previous version of this story misidentified the most common COVID-19 variant in the U.S. It is the alpha variant.

The Associated Press, NPR, Shahla Farzan from Missouri Public Radio, Hannah Meisel of Illinois Public Radio and Claudia Morell of WBEZ contributed to this report.

Katie O’Connell is the morning news editor for WBEZ. Follow her @katieoc.