A year into the coronavirus pandemic, Americans are anxious, depressed and frustrated — but also hopeful, as vaccines start rolling out to qualified people across the country.

But as the vaccine has arrived, so have the questions: What’s in the vaccine? Why two doses? Who should and shouldn’t get it? 

Here are the answers to your most frequently asked questions about the vaccine, including its  effectiveness, its risks, and what to expect when it comes to side effects.

When will I get the COVID vaccine?

Overall, vaccine distribution has been a patchy and confusing process nationwide, with some states rolling out faster than others.

Because there’s no overarching federal plan for vaccination, individuals need to check with their own states and counties to determine when they might get a shot. You can see your own state’s plan through a dropdown menu via the Center for Disease Control and Prevention’s coronavirus vaccine hub.

As we reported in January, when you will get the vaccine depends on your age and what you do for a living. It also matters where you live; New Jersey, for instance, started letting anyone with medical risk factors get vaccinated, while Los Angeles County stuck to a more restrictive tiered system. Some areas offered extra vaccine doses on a first-come, first-served basis, while others ran out.

In general, frontline health care workers are at the top of the list for shots, but states have discretion on who comes next. To speed up distribution, the federal government has given states the green light to vaccinate anyone over the age of 65, as well people over 16 with certain health conditions, such as diabetes, that would make them more likely to get severely ill if they contracted COVID-19. 

When can children get the vaccine?

Estimates vary, but kids as young as first grade might be able to get vaccinated against COVID-19 by September 2021, White House chief medical adviser Dr. Anthony Fauci said in early February. Vaccine makers have begun including children in clinical trials, with results expected in the coming months. 

But until those findings are evaluated, Pfizer’s vaccine is only authorized by the FDA for recipients ages 16 and up. Moderna’s shots are for ages 18 and up.

What are the differences between the COVID vaccines?

In December 2020, the FDA authorized emergency use of two coronavirus vaccines in the U.S., one made by Pfizer and BioNTech, and the other by Moderna. Both involve two doses, and both are made using messenger RNA, or mRNA, technology.

Traditionally, vaccines have been made from a weakened or inactivated germ that trains the immune system to fight off infection if it encounters the virus in the future. But mRNA vaccines do something different: They teach human body cells how to make a harmless piece of a protein — a “spike protein” — that’s also found on the surface of the coronavirus. After that protein piece emerges on the surface of a cell, the human immune system recognizes it and begins making antibodies for it — which offer protection if the person is exposed to the actual virus in the future.

The vaccine made by Pfizer needs to be kept very cold, between minus-112°F and minus-76°F, while the Moderna shot requires less extreme temperatures between minus-13°F and 5°F.

The only other major difference between the Pfizer and Moderna vaccines is the wait time between the two required doses. Pfizer’s are given 21 days apart, while the Modern shots are given 28 days apart.

Additional vaccine options are likely to become available soon. Johnson & Johnson is seeking FDA authorization for its single-dose vaccine, which has the advantage of being stored in regular refrigerators. A two-dose vaccine from Oxford and AstraZeneca is approved in the U.K. and European Union but not yet in the U.S.

Do the COVID vaccines protect against new variants? 

Health officials are tracking the spread of a number of variants of the coronavirus across the U.S., including a much more contagious version first identified in South Africa, another that’s rampant in the U.K., and one linked to travelers from Brazil. 

The CDC says the variant known as B.1.1.7, first seen in the U.K., is likely to become the dominant strain in the United States by March.

Citing preliminary studies, the CDC said the Pfizer and Moderna vaccines show signs of recognizing those variants. 

“I do think that the existing vaccines are going to offer reasonable protection against these new variants,” Dr. Scott Gottlieb, former head of the FDA, told CBS’ “Face the Nation” in early February, though he added that they are likely to be about 20% less effective against the new strains from Brazil and South Africa. Vaccine researchers are working on developing possible booster shots to combat variants if needed in the future.

South Africa suspended the start of its Oxford-AstraZeneca inoculation program in early February over concerns the shot doesn’t work as well against the variant there.

What are the known side effects of the COVID vaccine? 

In general, side effects are not uncommon with vaccines, and the COVID-19 shot is no exception. Your body’s immune reaction could include the same kinds of side effects often seen with other vaccines, including a sore arm, fatigue, fever, chills or headaches.

“This is expected,” Dr. Neeta Ogden, an internal medicine specialist and immunologist, said in an interview on CBSN.

“People should maybe think about vaccinating on weekends, for example,” she said. “You probably might need to take a day off from work. … This is predictable and I don’t think that it is alarming.”

Not everyone experiences side effects, but doctors stress that their occurrence is normal and should not discourage people from getting the shots. 

Who shouldn’t get a COVID vaccine?

Like most vaccines, this one may not be for everyone. The CDC says people allergic to the ingredient polyethylene glycol (PEG) or polysorbate, which is similar, should not get an mRNA COVID vaccine, and anyone who has an immediate allergic reaction to the first dose should not get the second one.

A handful of people suffered adverse reactions, including anaphylaxis, after getting the vaccine, but all recovered.

People with a history of allergic reaction to a vaccine or injectable therapy for another disease should talk to their doctors, the CDC advises. It says people with food allergies do not need to avoid the vaccine.

Should you get a COVID vaccine during pregnancy?

The CDC, the World Health Organization and the American College of Obstetricians and Gynecologists all advise pregnant patients to talk with a doctor about whether to get a vaccine. Pregnant people were not included in the clinical trials, so data is lacking, and the official guidance has left some confused. Many doctors, however, believe the shots are a good idea because of the known risk of severe illness from COVID-19 during pregnancy.

“I recommend highly that all pregnant women be immunized, from initial discovery of the pregnancy right up to term,” Dr. Bob Lahita, professor of medicine New York Medical College and chairman of medicine St. Joseph University Hospital, said on CBSN. He said there is “no evidence” that the vaccine “has any effect on the placenta, on the fetus, on the mother. Except if one gets the infection, the COVID, and you are pregnant, you run the risk of becoming very, very sick.”

How long will COVID vaccine protection last? 

Researchers and health experts say they don’t know for sure. On its official web FAQ, the CDC says, “We won’t know how long immunity lasts after vaccination until we have more data on how well COVID-19 vaccines work in real-world conditions.”

That said, Moderna CEO Stephane Bancel has offered a rough window: “We believe there will be protection potentially for a couple of years.” 

Can you still spread COVID after getting the vaccine?

People who receive a vaccine dramatically lower their chance of getting sick from the virus, but the vaccine trials did not determine whether a person could still be infectious after getting immunized. 

“We just do not know yet the answer to (that) question,” said Dr. Jaime Sepulveda, executive director of the Institute for Global Health Sciences at the University of California, San Francisco. “The clinical trials were not designed to have that as an endpoint.” 

Do I still need to wear a mask after receiving a COVID vaccine? 

Once you’ve gotten vaccinated it takes several weeks for the body to develop immunity, so you’ll need to continue taking precautions like social distancing and wearing masks to reduce your risk of infection during that time.

Even after that, experts say that until we get more information on the extent to which vaccinated people might still be able to spread the virus, people should continue practice social distancing and wear masks. Over time, as more people get vaccinated and infection rates decline, it may become safe to ease up.

“Eventually I think we won’t [need masks], but I think until we know that this vaccine is working, we are going to have to wear a mask,” pediatrician Dr. Dyan Hes told CBSN.

Can employers force you to get vaccinated?

The federal government doesn’t require vaccinations for anyone. But state and local governments might for their employees. And individual businesses can, in general, impose similar requirements.

“Generally speaking, employers are free to require safety measures like vaccination with exceptions for certain employees,” said Aaron Goldstein, a labor and employment partner at the international law firm Dorsey & Whitney. “So the answer is likely to be yes, with an asterisk.” Many hospitals, for example,  require staff to get vaccines, with exemptions allowed for medical or religious reasons.

American workers largely back employers making that call. Nearly half of employees — 46% — support their employers requiring COVID-19 shots, according to a survey of LinkedIn users. The survey showed 40% of employees do not support the move and 14% said they were unsure.

Do I need to get vaccinated if I’ve already had COVID?

Even after you’ve gotten sick from COVID-19 and recovered, you could still get it again; experts do not know how, for sure, long someone might carry antibodies after a bout with coronavirus. So-called natural immunity varies from person to person. The vaccines, on the other hand, provide a reliably high level of protection.

That said: If you were treated with monoclonal antibodies or convalescent plasma during your illness, you should wait 90 days before getting a COVID-19 vaccine. The CDC also recommends you should talk to your doctor before proceeding.

What are the ingredients in COVID vaccines?

Both government-approved vaccines are free of eggs, preservatives, or latex. A full list of ingredients can be found on the CDC’s website.

Why are the Pfizer and Moderna vaccines two doses?

For these vaccines to reach maximum effectiveness, two doses are needed. The first injection starts building protection in the immune system. A second shot increases the amount of that protection to more than 90% against the virus.

In reporting on this issue, CBS MoneyWatch senior reporter Stephen Gandel uncovered concerns that getting only one of the two shots might actually make the pandemic worse over time.

“The concern is that if people get one shot, and not two shots, and those people get exposed to the coronavirus, the virus won’t get killed off [from] them… and the virus will figure out a way to adapt itself, and then it could spread again. Then we could have a vaccine-resistant strain of the coronavirus out there,” he explained.

But so far, data from the CDC shows 96% of people are returning for their second shot on or close to schedule.

How many people need to be vaccinated before we reach herd immunity?

Experts haven’t reached a consensus on exactly what it will take for the world to achieve herd immunity — a level of widespread protection that leaves the virus few remaining targets, so outbreaks can no longer flourish. 

The bulk of the U.S. population will need to be vaccinated before it can happen; 50% won’t be enough, Dr. Anthony Fauci, the nation’s top infectious diseases expert, has said. 

Millions more doses will be rolling out to vaccination sites and pharmacies across the country in the months ahead, moving us closer to that goal. “By the time we get to April, that would be what I call for lack of better wording, open season. Namely, virtually everybody and anybody in any category can start to get vaccinated,” Fauci said.