Can the vaccine give me COVID-19? Which vaccine should I take? We answer your questions.

More than 63,000 people outside Chicago have received the first doses of Pfizer's COVID-19 vaccine a week into the state's immunization effort.

As Moderna adds to the supply, here are answers from suburban experts to common questions about the vaccines.

How the vaccines work

Q. Can the vaccine give me COVID-19?

A. The Pfizer-BioNTech and Moderna vaccines do not contain the virus itself. The groundbreaking vaccines use messenger RNA, or mRNA, technology to deliver a piece of genetic material that instructs your cells to make the spike protein found on the surface of the coronavirus, inducing an immune response. Your body then produces antibodies to the spike protein to prevent the actual virus from binding to cells.

It's not a novel strategy, said Dr. Paul Offit, a member of the Food and Drug Administration advisory committee that endorsed the leading vaccines.

“This particular notion of using messenger RNA as a vaccine has been around for 20 years,” Offit said during a panel discussion last week.

Q. What side effects can I expect?

A. Some possible side effects may include pain at the injection site, fever, fatigue, headache or chills. Those are signs that the vaccine is triggering an immune response as intended.

In clinical trials, those reactions were more frequent after the second dose of the vaccine.

So far, Northwestern Medicine Central DuPage Hospital in Winfield has had no reports of severe reactions, said Dr. Kevin Most, chief medical officer.

“Actually, of the total that we've done, which is a couple thousand now, we haven't had anybody that took a day off or needed to take a day off because of side effects,” Most said Monday.

Q. Will the vaccines protect against the new coronavirus variant circulating in the United Kingdom?

A. That's under review by U.S. Army scientists at the Walter Reed Army Institute of Research. “The initial look is that it really won't impact the vaccine, and it'll still be very effective,” Most said.

Distributing vaccines

Q. Who's next in line after health care workers and nursing home residents?

A. This week, an advisory committee for the Centers for Disease Control and Prevention recommended that the so-called Phase 1b of the vaccine rollout prioritize people 75 and older and front-line essential workers. About 49 million Americans fall into that category.

Then in Phase 1c - targeting 129 million people - vaccines should be offered to people 65 to 74, people 16 to 64 with high-risk medical conditions, and other essential workers, the committee said.

Essential workers recommended for Phase 1c vaccination include those in the food service, finance, information technology, transportation and logistics, energy, media and legal industries.

Q. How long will it take to move through the allocation phases?

A. DuPage County public health authorities expect it may take several months before reaching Phase 1c. A county health department spokeswoman said Tuesday officials are several weeks away from vaccinating the remainder of the estimated 43,000 health care personnel in DuPage in Phase 1a.

Q. What will distribution look like for high-risk people?

A. It's still unclear if doctors' offices or pharmacies will help deliver vaccines as distribution ramps up.

Advocate Aurora Health currently has no plans to open drive-through vaccination sites. The system operates 26 hospitals in Illinois and Wisconsin.

The DuPage health department is working with hospitals, health care providers, pharmacies and community leaders on “flexible COVID-19 vaccination programs that can accommodate different vaccines and scenarios,” the spokeswoman said. “Our goal is to make vaccine available through as many locations as possible.”

If you're part of Phase 1c because of a medical condition, you should consult your physician about vaccine plans, Most said.

Q. Does it matter which vaccine I get?

A. Medical experts say they would take either of the leading vaccines. It's a matter of availability. As vaccines become more widely available and more data is collected, one type may work better for one subpopulation, but right now, take which one you can get, Most said.

Vaccine safety

Q. Should pregnant or breastfeeding women get the vaccine?

A. Pregnant women were excluded from the vaccine clinical trials and should talk with their doctor about the potential risks and benefits.

“The fact of the matter is the SARS-CoV-2 virus, when it infects pregnant women, can infect them especially severely,” Offit said, “and so that's the other side of not getting the vaccine.”

Q. What about people with allergies?

A. People who have ever had a severe allergic reaction to any ingredient in a COVID-19 vaccine should not receive it, the CDC has advised.

“If you have had a severe allergic reaction to other vaccines or injectable therapies, you should ask your doctor if you should get a COVID-19 vaccine,” the federal guidelines state.

The CDC has reported six cases of anaphylaxis, a severe allergic reaction, in people who got the COVID-19 vaccine.

Some physicians are “kind of on the fence right now” about what to do with patients who carry an EpiPen, or epinephrine injectors, Most said.

“Really, it's those with severe allergies to IV's, severe allergies to any food preparations, where you need to carry that EpiPen to treat yourself. Those are the ones we're saying, 'Let's hold off for a little bit until we get a little bit more information,'” Most said.

Q. What precautions are in place for administering vaccines?

A. Those giving vaccines to people with a history of severe allergic reactions will ask them to wait for 30 minutes for observation, so if they do develop an allergic reaction, medical personnel could reverse it with a shot of epinephrine. Everyone else should wait for 15 minutes.

Looking ahead

Q. If I get the vaccine, why do I still have to wear a mask?

A. It's unclear if the newly vaccinated can still transmit the virus, but there's at least a theoretical risk, said Dr. Robert Citronberg, Advocate Aurora's executive medical director of infectious disease and prevention.

You could still acquire the virus, it could live in your nose and you could spread it to other people, even though you've been immunized and may not fall ill, Citronberg said during a virtual town hall.

Q. How many people will need vaccinations to reach herd immunity?

A. Herd immunity rates are based on how contagious a virus is, Most said. Dr. Anthony Fauci, the country's top immunologist, has said between 75% and 85% of the population would have to be vaccinated to achieve herd immunity. For measles, by comparison, the threshold is 93% to 95%.

“With 5% population of the population being infected, we certainly have quite a ways to go before we are even talking about the possibility of complete herd immunity,” Most said.