More and more people across Illinois are testing positive for COVID-19, and Chicago is expected to soon enter a "high" alert level under guidelines set by the Centers for Disease Control and Prevention.

And, according to the CDC, the new subvariant of omicron is now the dominant strain of COVID in the United States, with BA.2.12.1 responsible for nearly 58% of new cases over the last week.

As more cases are reported and the illness continues to spread, many are turning to questions over treating the virus with Pfizer's new Paxlovid antiviral COVID-19 pill.

Pfizer's Paxlovid pill has been used in several recent high-profile cases, including Vice President Kamala Harris.

As doctors continue to prescribe the drug, new questions are emerging about its side effects, why a small number of patients appear to relapse and more.

Here's what we know so far.

According to Pfizer, possible side effects of Paxlovid are: 

Pfizer warned additional side effects could also be possible.

Paxlovid was approved for emergency use in those 12 years and older, weighing at least 88 pounds who are at high risk of progressing to severe disease. The pill must be prescribed by a doctor.

"Patients in the authorized population with a risk factor for progression to severe COVID-19 are eligible for Paxlovid under the EUA even if they are fully vaccinated," the FDA stated. "Patients do not have to have more than one risk factor to be considered 'high risk.'"

According to Chicago Department of Public Health Commissioner Dr. Allison Arwady, the CDC's 10-day quarantine period applies to those who test positive for COVID whether Paxlovid's five-day course has been taken or not.

"So remember, this is all in that same 10-day window and we want you isolating, we want you staying home, while you have symptoms in that in that window," Dr. Arwady said in a Facebook Live Tuesday , in reference to patients who have taken the drug.

"So if you are somebody who -- although this doesn't happen that often -- if you take Paxlovid and you're feeling well, and then your symptoms get a little worse...you should stay home until you know until you're feeling better and obviously stay in touch with your doctor."

Paxlovid consists of three three pills taken twice a day for five days.

Experts say there is still much to be learned about the drug, which was authorized in December for adults at high risk of severe COVID-19 based on a study in which 1,000 adults received the medication.

Doctors have started reporting rare cases of patients whose symptoms return several days after completing Paxlovid's five-day regimen of pills. That's prompted questions about whether those patients are still contagious and should receive a second course of Paxlovid.

Last month, the Food and Drug Administration weighed in. It advised against a second round because there’s little risk of severe disease or hospitalization among patients who relapse.

Dr. Michael Charness reported last month on a 71-year-old vaccinated patient who saw his symptoms subside but then return, along with a spike in virus levels nine days into his illness.

Charness says Paxlovid remains a highly effective drug, but he wonders if it might be less potent against the current omicron variant. The $500 drug treatment was tested and OK'd based on its performance against the delta version of the coronavirus.

“The ability to clear the virus after it’s suppressed may be different from omicron to delta, especially for vaccinated people,” said Charness, who works for Boston's VA health system.

Could some people just be susceptible to a relapse? Both the FDA and Pfizer point out that 1% to 2% of people in Pfizer’s original study saw their virus levels rebound after 10 days. The rate was about the same among people taking the drug or dummy pills, “so it is unclear at this point that this is related to drug treatment,” the FDA stated.

Some experts point to another possibility: The Paxlovid dose isn’t strong enough to fully suppress the virus. Andy Pekosz of Johns Hopkins University worries that could spur mutations that are resistant to the drug.

“We should really make sure we’re dosing Paxlovid appropriately because I would hate to lose it right now,” said Pekosz, a virologist. “This is one of the essential tools we have to help us turn the corner on the pandemic.”

Pfizer tested Paxlovid in the highest-risk patients: unvaccinated adults with no prior COVID-19 infection and other health problems, such as heart disease and diabetes. The drug reduced their risk of hospitalization and death from 7% to 1%.

But that doesn’t reflect the vast majority of Americans today, where 89% of adults have had at least one shot. And roughly 60% of Americans have been infected with the virus at some point.

“That’s the population I care about in 2022 because that’s who we’re seeing -- vaccinated people with COVID -- so do they benefit?” asked Dr. David Boulware, a University of Minnesota researcher and physician.

There's no clear answer yet for vaccinated Americans, who already have a hospitalization rate far below 1%.

That may come from a large, ongoing Pfizer study that includes high-risk vaccinated people. No results have been published; the study is expected to wrap up in the fall.

Pfizer said last year that initial results showed Paxlovid failed to meet the study’s goals of significantly resolving symptoms and reducing hospitalizations. It recently stopped enrolling anyone who's received a vaccination or booster in the past year, a change Boulware says suggests those patients aren’t benefitting.

At a minimum, the preliminary data should be released to federal officials, Boulware said. “If the U.S. government is spending billions of dollars on this medicine, what’s the obligation to release that data so that they can formulate a good policy?"

Pfizer recently reported that proactively giving Paxlovid to family members of people infected with COVID-19 didn’t significantly reduce their chances of catching it. But that's not the end of the story. Pfizer is studying several other potential benefits of early use, including whether Paxlovid reduces the length and severity of COVID-19 among households.

“It's a high bar to protect against infection but I’d love to see data on how Paxlovid did against severe disease because it may be more effective there,” said Pekosz.