COVID-19 Vaccine Frequently Asked Questions

Get answers to common and evolving questions around a COVID-19 vaccine.

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You may. People with moderately to severely compromised immune systems are especially vulnerable to COVID-19 and may not build the same level of immunity to a two-dose vaccine series compared to people who are not immunocompromised. For these individuals, CDC recommends an additional dose of mRNA COVID-19 vaccine at least 28 days after a second dose of the Pfizer-BioNTech or Moderna COVID-19 vaccine for these individuals.

A vaccine booster is now also recommended if you received the Pfizer-BioNTech vaccine, are over 65 and/or are at higher risk of serious complications from the disease to speak with your healthcare provider about getting a Pfizer COVID-19 booster vaccine.

For more information on booster doses visit the Centers for Disease Control and Prevention website.

While there is no preference to the three available vaccines, they are not interchangeable. If you begin your vaccination series with the Pfizer vaccine your second dose should be Pfizer, and if you begin with the Moderna vaccine your second dose should be Moderna. The Johnson & Johnson vaccine requires only one dose.  

Yes. So far, studies suggest that the currently available vaccines work on variants circulating across the U.S. and globe. Many of the more common variants allow the virus to spread more easily, making it especially important to get vaccinated as soon as possible. If you are not yet fully vaccinated, protect yourself by following recommendations for wearing a face mask and maintaining social distance. And maintain good health practices such as washing your hands and avoiding unnecessary exposure to people who are sick.

You can view reports from the CDC showing which variants are currently most common in the United States.

Yes. It is important for everyone to get vaccinated as soon as they are eligible because this will help reduce the transmission of COVID-19 overall, as well as provide protective immunity for the individual who is vaccinated. I encourage you to speak with your child’s healthcare provider about any concerns you have.

Currently there is one vaccine, made my Pfizer-BioNTech, that is authorized for use by everyone 12-15 year-olds.

Before Getting Vaccinated

State health departments are providing information on when and where vaccines are available. Find your state health department using our lookup tool. You can also search for availability through your local pharmacy by visiting

No. Like the flu shot and other vaccines, COVID-19 vaccines cannot give you the virus.

Yes. Due to the severe health risks associated with COVID-19 and the fact that reinfection with COVID-19 is possible, you should be vaccinated regardless of whether you already had COVID-19 infection. If you were treated for COVID-19 symptoms with monoclonal antibodies or convalescent plasma, you should wait 90 days before getting a COVID-19 vaccine. Talk to your doctor if you are unsure what treatments you received or if you have more questions about getting a COVID-19 vaccine.

Experts do not yet know how long someone is protected from getting sick again after recovering from COVID-19. The immunity someone gains from having an infection, called “natural immunity,” varies from person to person.  It is rare for someone who has had COVID-19 to get infected again. It also is uncommon for people who do get COVID-19 again to get it within 90 days of when they recovered from their first infection. We won’t know how long immunity produced by vaccination lasts until we have more data on how well the vaccines work.

We also do not know if natural immunity protects someone from the new circulating variants.

Having seasonal or food allergies does not mean you will experience a reaction to the vaccine.  If you have a history of severe allergic reactions you should talk to your physician before receiving an mRNA COVID-19 vaccination. They will help you determine if you have experienced a severe allergic reaction (e.g., anaphylaxis) to any component of a COVID-19 vaccine listed in the prescribing information, in which case the vaccine would not be recommended. Established COVID-19 vaccination protocols suggest all persons be observed after vaccination for a minimum of 15 minutes.

Yes. Whether you are trying to get pregnant now, or want to get pregnant in the future, you may get a COVID-19 vaccine that protects you against severe illness from COVID-19. Misinformation is circulating and that can be confusing. There isn’t any evidence that any of the COVID-19 vaccines currently available cause problems with pregnancy or the development of the placenta. There has never been any evidence of fertility problems as a side effect for any vaccine, including COVID-19 vaccines. Speak with your healthcare provider if you have concerns so they can help you address them with science-based information.

COVID-19 vaccine safety is a top priority. Any health issues related to a vaccination are taken seriously and researched thoroughly. Since COVID-19 vaccines became available, healthcare providers have been asked to report adverse events to the Vaccine Adverse Event Reporting System. The system is effectively working. Over 177 million people have received at least one dose of an mRNA vaccine from Pfizer and Moderna, and rare cases of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) following vaccination have emerged in over 1,000 cases, primarily in men under 30.  Most individuals who received care were treated and quickly felt better. The Centers for Disease Prevention and Control (CDC) has issued a “likely association” and plans to add wording about myocarditis and symptoms to the vaccine fact sheets. Further findings will continue to be researched and shared publicly.

The benefits to COVID-19 vaccination still outweigh the risks and we encourage everyone 12 years and up to be vaccinated.

No, vaccines were granted emergency use authorization because they are deemed safe and effective. The U.S. Food and Drug Administration’s (FDA’s) Center for Biologics Evaluation and Research is responsible for regulating vaccines in the United States. And each vaccine producer must follow a multi-step approval process that includes sharing research from clinical trials.  

FDA can also require a manufacturer to submit the results of their own tests for potency, safety, and purity for each vaccine lot. Vaccines typically require years of research and testing before reaching the public, but scientists banded together across the globe to produce a safe and effective coronavirus vaccine more quickly.  This doesn’t mean that the vaccine is less safe, it just means that the whole world is keen to ensure that we are protected from this new threat to lung health and so researchers have been working collaboratively to build a knowledge base of what works and achieved success quickly. 

The CDC has more information about COVID-19 vaccine safety.

After approving a vaccine, FDA continues to oversee its production to ensure continuing safety. Monitoring of the vaccine and of production activities, including periodic facility inspections, must continue as long as the manufacturer holds a license for the vaccine product. 

V-safe is a smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after you receive a COVID-19 vaccination. Through v-safe, you can quickly tell CDC if you have any side effects after getting the COVID-19 vaccine. Depending on your answers, someone from CDC may call to check on you. And v-safe will remind you to get your second COVID-19 vaccine dose if you need one. 

In addition, the Vaccine Adverse Event Reporting System (VAERS) is a national vaccine safety surveillance program that collects and analyzes side effects that occur. Reports from patients, providers, pharmacists and vaccine manufacturers can all be submitted to VAERS.   

The CDC has more information about COVID-19 vaccine safety.

Choosing a Vaccine

Health experts agree that the best vaccine is the one that is available to you. There are three types of vaccines that work in different ways:

  • Messenger RNA (mRNA) vaccines contain a copy of genetic information that looks like the SARS-CoV2 (the virus that causes COVID-19) virus’s information that causes COVID-19.  This gives our cells instructions for how to make a harmless protein that is unique to the virus. After our cells make copies of the protein, our bodies recognize that the protein should not be there and build T-lymphocytes and B-lymphocytes and antibodies that will remember how to fight the virus that causes COVID-19 if we encounter the virus in the future. The Moderna and Pfizer vaccines are mRNA vaccines. 
  • Viral vector vaccines contain a modified, weakened virus (not the COVID-19 virus) that delivers a message for a protein like the spike protein of the SARS-CoV2 virus to be made by our cells.  By instructing cells to make large amounts of antigen, which then triggers an immune response, the vaccine mimics what happens during natural infection with SARS-CoV2 and stimulates an immune response that will protect you from future encounters from the COVID-19 virus. The AstraZeneca and Johnson & Johnson vaccines are examples of these. 
  • Protein-based vaccines contain harmless coronavirus proteins, not the whole virus, and produces an immune response against the virus. The Novavax vaccine is an example of protein-based vaccines.

The Lung Association, along with other public health experts, recommend getting any of the vaccines available to you as all have been shown to protect against COVID-19. 

Comparing the efficacy of the three vaccines is a bit like comparing apples and oranges because the Johnson & Johnson/Janssen vaccine set out to answer a different question (does it protect against moderate to severe illness?) than the Pfizer-BioNTech and Moderna vaccines (do they prevent symptomatic infection?). Therefore, the different efficacy percentages can lead to confusion if you try to compare them looking only at the numbers.

In clinical trials both the Pfizer and Moderna vaccines have shown approximately 95% efficacy, which is very promising. This means that in the clinical trials, the vaccine prevented 95% of the clinical cases compared to the placebo group recipients. The Johnson & Johnson/Janssen vaccine is also very promising and has been shown to be 66% protective against moderate to severe illness, and 85% effective against severe illness.  However, it’s important to note that we don’t know what will happen in the “real world” until researchers can evaluate those who have been vaccinated down the line.

Different types of vaccines require different types of administrations. For some types of COVID-19 vaccines, the first shot would prime the immune system, helping it recognize the virus and the second shot would strengthen the immune response. Both the Pfizer and Moderna vaccines require two doses: 21 days apart for the Pfizer vaccine and 28 days apart for the Moderna vaccine. The Johnson & Johnson vaccine is one dose.  

A second dose of mRNA COVID-19 vaccine should not be received earlier than the recommended schedule.

The second dose of COVID-19 vaccine should be administered as close to the recommended interval as possible. If this is not an option, the second dose can be given up to six weeks (42 days) after the first dose is given. There is limited efficacy data beyond this window but, it is recommended that if you go beyond this window, the vaccination series does not need to restart.

No. The two-dose vaccines are not interchangeable with each other, nor should they be combined with the Johnson & Johnson vaccine that is only one dose. Stick with the same type of vaccine for both doses if you receive Pfizer or Moderna COVID-19 vaccine.

After Getting Vaccinated

Once you're fully vaccinated (2 weeks after second dose of Pfizer or Moderna vaccines, or 2 weeks after a single-dose Johnson & Johnson vaccine) you can start doing some activities you had to stop because of the pandemic. The CDC has more guidance on how to be safe once you're fully vaccinated.

New guidance from the CDC recommends mask wearing in public indoor settings if you are in an area with substantial or high transmission. You can check community transmission using CDC's Data Tracker. Other reasons to consider wearing a mask when inside public indoor settings include if you are immunocompromised, at increased risk for severe disease or have someone in your home who is one of those or not fully vaccinated. Vaccination remains the best protection against severe illness from COVID-19, yet rising cases and hospitalizations caused by the highly transmittable Delta variant warrant further protection against the growing community spread occurring in much of the country.

We only have preliminary data so far, based on phase 1 and 2 clinical trials, so it’s too early to fully report on side effects. In trials for the top vaccine candidates, Pfizer and Moderna, participants have said they experienced symptoms including fever, muscle aches, bad headaches and fatigue after receiving the shots, but the side effects generally did not last more than a day. Still, preliminary data suggests that, compared with most flu vaccines, the coronavirus shots have a somewhat higher rate of such reactions, which are almost always normal signs that the body’s immune response is kicking in.

The independent board that conducted the interim analysis of Moderna’s large trial found that severe side effects included fatigue in 9.7% of participants, muscle pain in 8.9%, joint pain in 5.2% and headache in 4.5%. For the Pfizer vaccine, the numbers were lower: Severe side effects included fatigue (3.8%) and headache (2%).

A key reason to get vaccinated is to protect against having severe complications up to and including death, especially among those who are in the high-risk group.

So, although it is important to be aware of safety and side effect issues around the vaccine, each person should weigh these usually mild side effects of arm soreness and fatigue for a day or two against the great benefit of  protecting against moderate to severe illness which can occur at any age and in people without any underlying conditions.

If you have pain or discomfort following your COVID-19 vaccine, speak with your healthcare provider about taking an over-the-counter medication like ibuprofen or acetaminophen. It is important to take pain reliever after the vaccination, not before.

If you are experiencing pain where you got your shot you could try applying a clean, cool, wet washcloth to the injection area and be sure to use or exercise your arm. If you are experiencing discomfort from a fever, drink plenty of fluids, dress lightly.

Remember that side effects may be more intense after your second shot and are normal signs that your body is building protection and should go away within a few days.  You should contact your healthcare provider if the redness or tenderness where you got your shot gets worse after 24 hours or if your side effects are worrying you and not gone after a few days.  

Millions of people in the United States have received COVID-19 vaccines and they are safe and effective at protecting against COVID-19. Some people experience no side effects after vaccination while many will experience mild side effects, such as pain, swelling at the injection site, a headache, chills or a fever. A small number of individuals will experience a severe allergic reaction to an ingredient in the vaccine, but that is extremely rare and the reason for observation immediately after being vaccinated. Any time you experience symptoms that worry you it is time to discuss them with your healthcare provider.

You can help monitor for side effects using V-safe, a smartphone-based health checker if you have received a COVID-19 vaccine in the past six weeks. Using text messages and web surveys, it allows individuals who track any side effects and will follow up via phone with anyone who reports a medically significant adverse event.

It depends. Immunity is when the body can resist a particular disease, and vaccines help build up that immunity by stimulating antibody production and immune cells (T and B lymphoctyes) for future protection. Immunity works best at the community level so when enough people are vaccinated then an infected individual has nobody to spread the disease to. A vaccination can help prevent getting the infection or at least keeping the severity of the infection to a mild level. Everyone’s immune system responds a little differently.

That is possible, but uncommon. What you are referring to is also called breakthrough cases, and there have been instances of fully vaccinated individuals who became ill with COVID-19. No vaccine is 100% effective. In clinical trials, the available vaccines showed an efficacy of between 72% - 95% in protecting against moderate-to-severe illness. That high level of immunity against SARS-CoV-2, which we had no immunity whatsoever from pre-pandemic, is a huge advantage to protecting your health. However, until more people are vaccinated, and COVID-19 is no longer widely circulating, we’ll continue to see a small number of individuals become ill after being vaccinated. Health experts are researching these individuals to determine if any further guidance is warranted. Learn more at

This is currently unknown. When we know how long immunity from the vaccine will last, decisions can be made about timing of re-vaccination.

Have a question not addressed in our FAQ? Contact our Lung HelpLine at 1-800-LUNGUSA for one-on-one support, or submit your question online.

The American Lung Association urges members of the public to always consult with their own healthcare providers about whether this or any vaccine is appropriate for them.

Page last updated: September 27, 2021

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