Originally Published: 17 AUG 21 13:21 ET

Updated: 17 AUG 21 13:45 ET

By Katia Hetter, CNN

(CNN) -- With the Biden administration expected to announce that booster doses will be needed for most people who received the Covid-19 vaccine, many people have questions: Are boosters safe? Does the fact that we may need boosters mean that the vaccine isn't working? And who should get them?

To get the answers, we turned to CNN Medical Analyst Dr. Leana Wen. Wen is an emergency physician and visiting professor of health policy and management at the George Washington University Milken Institute School of Public Health. She's also author of a new book, "Lifelines: A Doctor's Journey in the Fight for Public Health."

CNN: Are boosters unusual when it comes vaccines?

Wen: Not at all. Let's first define what we mean when we say booster. Many vaccines require multiple doses to achieve the full immune effect. The polio vaccine, for example, requires four doses. The hepatitis vaccine requires three doses. These vaccines are a series, meaning that the second, third or fourth doses are needed to achieve full immune protection. Most people are done for a lifetime once they've completed the full series.

There are other vaccines that require occasional "boosts" because immunity may wane over time. The tetanus-diphtheria vaccine is such an example. This is part of a series of childhood immunizations. Then, as adults, we are still supposed to receive this vaccine every 10 years.

There are other vaccines that need to be administered even more often. The influenza vaccine needs to be updated every year because there are so many new strains every season. This is not so much to boost our immunity, but because there are new strains targeted by the vaccine.

Needing additional shots of a vaccine is not at all unusual. Covid-19 is a relatively new disease that's come about only in the last two years, and we don't yet know if one more dose is required because there needs to be say, a three-dose series like hepatitis; if there may be occasional "boosts" immunity like tetanus; or if new strains may emerge and we may need shots to target these strains.

CNN: Does a booster mean that the vaccine isn't working?

Wen: No. We are still learning about Covid-19, and it may be that a third booster shot is needed to finish the series, and after that, we don't need additional immunity. It may also be that immunity diminishes over time, and that an occasional booster will help increase immunity.

The Covid-19 vaccines are safe and very effective. According to estimates from US Centers for Disease Control and Prevention data, the vaccines protect us from severe illness by about 25 times. That's the biggest reason why we get vaccinated -- to reduce the likelihood of being hospitalized or dying.

Vaccination also reduces the chance of getting Covid-19 by about eight times. A vaccinated person is much less likely to get sick from Covid-19, compared to someone who is not vaccinated. That person is also therefore less likely to spread coronavirus. These are all very compelling reasons to get vaccinated -- to protect yourself and others around you.

CNN: Are boosters safe?

Wen: Yes. We routinely receive additional shots for other vaccines. These studies of an additional booster dose are being carefully conducted in the US and other countries. Some other countries, like Israel and Germany, have already authorized third booster doses. If a Covid-19 booster is authorized, it will have been studied in many people to make sure it is safe.

CNN: Who should be getting boosters at this time?

Wen: That's something our federal health officials are looking into now. They have already said that people who are moderately or severely immunocompromised, who received the two-dose Pfizer or Moderna vaccines, can receive a third dose now. More guidance is expected soon for other groups.

For right now, I'd advise that you speak with your doctor. The decision for a booster dose is probably not a one-size-fits-all recommendation, but an individualized decision depending on your medical circumstances.

CNN: Some people may want to know what's the purpose of getting the vaccine if you have to get a booster later?

Wen: I understand this is a concern that some people raise, though there is a logical fallacy here. We don't say, well, what's the point of putting on a seatbelt today if I have to put on a seatbelt tomorrow, too? The vaccines protect you well. To have additional, ongoing protection, you may need a booster dose. Just because you may need more protection in the future, doesn't mean that you shouldn't get the initial protection afforded by the vaccine.

Ultimately, the Covid-19 vaccine is what will protect us and our loved ones -- and is key to ending the pandemic. A booster may be needed, and we should get it if and when it is advised.