About the current FDA-emergency use authorized COVID-19 vaccines

  • Are the vaccines safe?

    We will not recommend any vaccine that we do not feel is safe and effective. The COVID-19 vaccines have been tested using large-scale clinical trials with many thousands of people from different races, ages, and backgrounds. Every vaccine goes through a strict regulatory review process. We continually monitor any clinical or safety concerns for all vaccines. 

  • Are there concerns about serious side effects from the Johnson & Johnson (Janssen) vaccine?

    The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) amended information about the Johnson & Johnson (Janssen) COVID-19 vaccine because of a potential safety concern. There have been very rare reports of a type of blood clot called cerebral venous sinus thrombosis among patients that have received the Johnson & Johnson vaccine. Though very rare, the risk of certain blood clots appears to be highest in women aged 18-49.  

    The FDA and CDC have confidence that this vaccine is safe and effective in preventing COVID-19. The FDA has determined that the vaccine’s known and potential benefits outweigh its known and potential risks in individuals 18 years of age and older. At this time, the available data suggests that the chance of blood clots occurring is very low, but the FDA and CDC will remain vigilant in continuing to investigate this risk.

    Learn more on the FDA website

  • How does the Johnson & Johnson vaccine work?

    The Johnson & Johnson vaccine is not an mRNA vaccine. It is an adenovirus vector vaccine. It uses a modified version of the common cold virus called adenovirus 26 to deliver directions to your body to make the spike protein found on the surface of the coronavirus. Your immune system can then make antibodies to these proteins to protect you against COVID-19. You cannot get the cold from the vaccine.

  • The Pfizer and Moderna COVID-19 vaccines are mRNA vaccines. What does that mean?

    Though mRNA vaccines are a new kind of vaccine, researchers have been studying and working on them for many years. They do not contain live virus and cannot cause COVID-19. Instead, they give our cells directions on how to make the COVID-19 proteins found on the outside layer of the coronavirus. Our immune system can then make antibodies to these proteins and protect us from being infected with COVID-19. The mRNA from the vaccine never enters the nucleus of our cells or gets into our DNA. The CDC has information about mRNA vaccines.

  • Can I get COVID-19 from a vaccine?

    No. The vaccines (Pfizer, Moderna, or Johnson & Johnson) do not contain the whole or live virus and therefore cannot cause COVID-19.

  • How do we know the vaccines work? Is the Johnson & Johnson vaccine as effective at protecting against COVID-19 as the other vaccine options?

    All COVID-19 vaccines have proven to be extremely effective. According to Phase 3 trials, the Pfizer vaccine is 95% effective 7 days after the second dose. The Moderna vaccine is 94% effective 14 days after the second dose. These results were consistent across gender, age, race, and ethnicity.

    According to clinical trials, the Janssen (Johnson & Johnson) vaccine is 85% effective against severe COVID-19 disease. It also provides 100% protection against hospitalization and death from COVID-19. See information on the CDC website, as well.

  • How long will immunity last after I get vaccinated? Will I need to be vaccinated every year?

    We do not know this yet. The clinical trials will continue to monitor participants to see how long protection lasts. We will provide updated information as it becomes available.

  • Do I need a booster?

    At this time, there is no recommendation for a booster for any of the current FDA-approved COVID-19 vaccines (Pfizer, Moderna, or Johnson and Johnson). It is not yet known if boosters will be needed later. There are ongoing studies to see if boosters may be necessary.

    It is important, however, to make sure you get the first and second dose if you got the Pfizer or Moderna COVID vaccines.

  • I already had COVID-19. Should I get vaccinated?

    Yes, you can still get vaccinated if you have had COVID-19 and have recovered.

    However, you should not get vaccinated if:

  • What are the common side effects of a COVID-19 vaccine?

    Some people do get side effects after receiving the vaccine. For most people, mild side effects resolve within a day or so.

    • The most commonly reported symptoms from the Pfizer vaccine are pain at the site of vaccination, fatigue, headache, muscle pain, joint pain, and chills. 
    • The most commonly reported symptoms from the Moderna vaccine are pain at the injection site, tiredness, headache, muscle pain, chills, joint pain, swollen lymph nodes in the same arm as the injection, nausea and vomiting, and fever.
    • The most commonly reported symptoms from the Johnson & Johnson vaccine are pain at the injection site, headache, fatigue, muscle aches and nausea. 

    Read more about potential side effects

  • When am I fully vaccinated?

    You are considered fully vaccinated if it has been:

    • 2 weeks since getting the single-dose Johnson & Johnson vaccine or 
    • 2 weeks since getting the second dose of the Pfizer or Moderna vaccine

    If it’s been less than 2 weeks, you are not fully vaccinated. 

  • Do I need a COVID antibody test before or after I get a COVID-19 vaccine?

    Antibody testing is not currently recommended to assess for immunity to COVID-19 following COVID-19 vaccination or to assess the need to vaccination in an unvaccinated person.

Masks and social distancing

  • What about masking and social distancing?

    COVID-19 in the community is currently decreasing. You can find more information on: the CDC website, the Massachusetts state website, and the New Hampshire state website. Note that state and local guidelines may vary for masking and indoor/outdoor gathering. Your local town may have different guidelines so it is important for you to check your local guidelines. 

    Patients with solid organ transplants or who are immunocompromised should speak with their care team to discuss recommendations about masking and social distancing. 

    If you have symptoms, you should talk to your health care provider. You may need to be tested for COVID-19. See more information on the CDC website

    Please note: Patients and visitors to Mass General Brigham hospitals and health care facilities must continue to wear a facility-issued mask at all times when you are at our facilities. Employees will continue to do so, as well. This is for the health and safety of everyone in our care. View our mask policy.


  • Does the COVID-19 vaccines cause allergic reactions?

    There have been some reports of people having allergic reactions after getting vaccinated. A small number of people had a severe allergic reaction called anaphylaxis. Based on this, the U.S. Food and Drug Administration and the Centers for Disease Control and Prevention (CDC) recommend that people with a history of anaphylaxis to any of the ingredients in a COVID-19 vaccine should not get that vaccine. People with other food or medication allergies can be vaccinated.

    In general, most patients allergic to one vaccine can receive the other vaccines safely. If you have a history of severe allergic reactions to vaccines, injectable therapies, or any component of the COVID-19 vaccine you are going to receive, you should talk to your primary care provider or allergist (if you have one). Your provider can help you decide if it is safe to get vaccinated.  

    Read more about potential side effects

  • Can I get the COVID-19 vaccines if I have a food or drug allergy?

    You can receive a COVID-19 vaccine if you have a food or drug allergy. The Pfizer, Moderna, and Johnson & Johnson COVID-19 vaccines do not contain gelatin, egg, or latex. Nevertheless, if you have a history of anaphylaxis due to any cause (food, oral medications, venom, latex), you might be observed for 30 minutes after receiving the vaccine.

  • What are the ingredients in the COVID-19 vaccines?

    The Pfizer,  Moderna, and Johnson & Johnson COVID-19 vaccines do not contain gelatin, egg, or latex. Also, the vial stoppers are not made with natural rubber latex. Patients who have latex allergies can receive the Pfizer, Moderna, and Johnson & Johnson COVID-19 vaccines. 

    Both the Pfizer and Moderna COVID-19 vaccines contain polyethylene glycol. Reactions to polyethylene glycol are very rare. Patients with a history of having an allergic reaction to polyethylene glycol should talk to their provider before receiving either the Pfizer or Moderna vaccine. 

    Ingredients of the COVID-19 vaccines

    Scroll to the right to view the full table below.

      Pfzier-BioNTech Moderna Janssen (Johnson & Johnson)
    Active Nucleoside-modified messenger RNA (modRNA) encoding the viral spike (S) glycoprotein of SARS-CoV-2. Nucleoside-modified mRNA encoding the viral spike (S) glycoprotein of SARS-CoV-2 Recombinant, replication-incompetent adenovirus type 26 expressing the SARS-CoV-2 spike protein
    Inactive - lipids
    • (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate)
    • 2[(polyethylene glycol [PEG])-2000]-N,N-ditetradecylacetamide
    • 1,2-distearoyl-sn-glycero-3-phosphocholine
    • Cholesterol
    • SM-102 (Proprietary to Moderna) 
    • Polyethylene glycol (PEG) 2000 dimyristoyl glycerol (DMG)
    • 1,2-distearoyl-sn-glycero-3-phosphocholine
    • Cholesterol 
    • 2-hydroxypropyl-β-cyclodextrin (HBCD)
    • Polysorbate-80
    Inactive – salts, sugars, buffers 
    • Potassium chloride, monobasic potassium phosphate, sodium chloride, dibasic sodium phosphate dihydrate
    • Sugar (sucrose)
    • The diluent, added to the vaccine for administration, is saline (sodium chloride)
    • Tromethamine, tromethamine hydrochloride, acetic acid, sodium acetate
    • Sugar (sucrose)
    • No diluent needed
    • Citric acid monohydrate, trisodium citrate dihydrate
    • Ethanol
    • Sodium chloride
  • What is a vaccine allergy?

    Similar to medication or food allergies, people can be allergic to an ingredient in a vaccine. About half of allergic reactions to vaccines happen in the first 15 minutes after receiving vaccination, and 90% occur within the first 30 minutes. Most vaccine allergic reactions are mild, such as hives.

    A severe allergic reaction is called anaphylaxis, which are very rare, occurring in one in a million people for most vaccines. Symptoms of anaphylaxis almost always occur within 4 hours of vaccination, most often within minutes. Symptoms usually include multiple parts of the body: hives on the skin; swelling of mouth, lips, tongue or throat; shortness of breath, wheezing, or chest tightness; or low blood pressure or loss of consciousness.

  • What happens if I have a reaction to the COVID-19 vaccine?

    Because most allergic reactions happen within the first 15–30 minutes, all patients are observed for 15 minutes after getting vaccinated to watch for an allergic reaction. If you have a history of anaphylaxis, you may have a 30-minute observation period after getting vaccinated. If you do have an allergic reaction, medical staff will treat you immediately. All vaccine locations can diagnose and manage allergic reactions and have medications, including epinephrine (“Epi-Pen”), available.

Immunocompromised patients

  • I am immunocompromised. Should I get a COVID-19 vaccine?

    The CDC says that people who are immunocompromised may be vaccinated against COVID-19, as long as they have had no issues with getting vaccines in the past. For questions about allergies related to COVID-19 vaccination, please see the allergy frequently asked questions.

    Please note, the COVID-19 vaccines are not live vaccines; live vaccines are often not recommended for immunocompromised patients. 

    Patients who are immunocompromised include people:  

    • Living with HIV
    • On immunosuppressive therapies like steroids (prednisone) for a long time
    • On immunosuppressive therapies for prevention of organ transplant rejection
    • On immune altering medications like biologic therapies (often injectable). These are used for treatment of autoimmune diseases such as Crohn’s disease, rheumatoid arthritis, lupus, and others.

    We do not yet know how effective the COVID-19 vaccines will be for you. You may have less of an immune response when you get vaccinated. Even if you get vaccinated, you should still wear a mask, practice social distancing, and wash your hands. Please see the frequently asked questions about masks and social distancing. This is true for everyone getting vaccinated now. Infection control experts will let us know when it is safe to change or stop these safety measures. See below for more information.

    For now, we do not know if you may need long-term boosters or revaccination. Mass General Brigham may not start repeat vaccination until everyone is vaccinated.

  • Should I change my immunosuppression medications when I get the vaccine?

    In general, we do not recommend altering the immunosuppression before or after vaccination. In specific cases, your provider may recommend changes. If you have questions, discuss this during your next medical visit.

  • Can I get a COVID-19 vaccine if I have had an organ transplant?

    You can get vaccinated. It’s possible that a COVID-19 vaccination may be less effective for you. It may be best to wait to get vaccinated at least 3 months after your transplant, if possible, to improve the immune response to the vaccine you receive (when you are on less immune suppression). There is no preference for a specific COVID-19 vaccine if you are a transplant patient. Your transplant provider will tell you if you need transplant labs after vaccination.

  • If I’ve had a solid organ transplant, can I stop wearing a mask if I’ve been vaccinated?

    Solid organ transplant patients should remain vigilant in following COVID-19 precautions even if you have been vaccinated. We are still learning more about the level of protection after vaccination in organ transplant patients. 

    While the CDC has updated its guidelines for fully vaccinated people, your doctor may advise that you continue avoid gathering with individuals who are not in your household, even after you are vaccinated. We recommend that you:

    • Not gather with family/friends who do not live in your household, unmasked and less than 6 feet apart, despite their vaccination status. Vaccinated individuals might be able to spread the virus to others.
    • Wear a well-fitting mask when outside your home. 
    • Wash your hands frequently, especially before eating. 
    • Stay at least 6 feet (2 arms lengths) apart from others that don't live with you.
    • Avoid crowds and poorly ventilated spaces. The more people you are in contact with, the more likely you are to be exposed to COVID-19.
    • Do not travel at this time.

    Per CDC guidelines, we are not recommending antibody testing at this time. We are still testing the best methods to determine immunity. We do not know what level of antibodies would provide protection in transplant patients. We hope to have more information soon. 

  • I am waiting for organ transplantation. Should I get vaccinated?

    In general, vaccines work better before organ transplant, before the immunosuppression has started. If possible, we would recommend that you get vaccinated before transplant.

Pregnancy and breastfeeding

Mass General Brigham Maternal-Fetal Medicine Specialist Dr. Ilona Goldfarb answers your questions about pregnancy, fertility, and COVID-19 vaccination.

  • I am pregnant. Should I get vaccinated?

    Vaccinations are considered a safe and routine part of prenatal care. For example, the flu shot is not only offered during pregnancy but recommended.

    In line with recommendations from the Centers for Disease Control and Prevention (CDC), COVID-19 vaccines are available for patients who are pregnant. However, it is recommended that you speak with your OB provider about whether or not you should get vaccinated. Both the virus and the vaccines are new. As pregnant people were not included in the trials of the COVID-19 vaccines, safety data is limited. 

    With the help of your OB provider, you can discuss what is the best option for you. Your decision to be vaccinated during pregnancy should be based on your risk for exposure to the virus, how sick you might get if you do get the virus, and the latest available data about the vaccines.

  • I know the COVID-19 vaccines are new. Is there safety data for pregnant people?

    Like many new medications and vaccines, the COVID-19 vaccines were studied in pregnant animals and these studies did not show any complications related to fertility or reproduction from the vaccine exposure.  

    More than 30,000 pregnant individuals have received the Pfizer/BioNTech or Moderna vaccines in the U.S. since December 2020 and so far, the CDC is reporting that there are no safety concerns.

    While the Johnson and Johnson vaccine is the newest to be approved by the FDA, this type of vaccine has been used against other viruses in studies around the world. Some of these studies included pregnant individuals. No complications from these vaccine exposures have been reported.

    Read more about vaccination considerations from the CDC

  • If I decide to get vaccinated during pregnancy, does it matter when I get vaccinated?

    The decision about when you get vaccinated should be made together with your OB provider. This decision should take into account your risk of exposure to the virus and what your chance of getting very sick might be if you do get the virus. There is no data to suggest that the COVID-19 vaccines cause miscarriage.

  • I heard that some people had reactions after vaccination. Are these dangerous in pregnancy?

    Symptoms including fever, muscle aches, joint pains, fatigue, and headache are common side effects of the COVID-19 vaccines. Most mild side effects resolve within a day or two and are not believed to be dangerous. If you are worried about side effects from the COVID-19 vaccines and your pregnancy, talk to your OB provider before getting the vaccine.

    Read more about potential side effects

  • I am breastfeeding. Should I get vaccinated?

    The COVID-19 vaccines are currently being offered to breastfeeding individuals. At this time, there is no data regarding the health impact on breastfed infants of mothers who were vaccinated. However, any vaccine that makes it into the breast milk is likely to be quickly inactivated when the milk is digested. In addition, some of your COVID-19 immunity can pass to the baby through the breast milk after you receive the vaccine. The Academy of Breastfeeding Medicine recommends that all breastfeeding individuals get a COVID-19 vaccine.

  • Will getting vaccinated affect my chance of getting pregnant in the future?

    There is no evidence that these vaccines affect future fertility.

    In a joint statement, the American College of Obstetricians and Gynecologists (ACOG), the American Society for Reproductive Medicine (ASRM) and the Society for Maternal-Fetal Medicine (SMFM) shared that "there is no evidence that the vaccines can lead to loss of fertility. While fertility was not specifically studied in the clinical trials of the vaccines, no loss of fertility has been reported among trial participants or among the millions who have received the vaccines since their authorization, and no signs of infertility appeared in animal studies. Loss of fertility is scientifically unlikely.”

  • If I receive either the Pfizer/BioNTech or the Moderna vaccine, what if I become pregnant between the first and second doses?

    You can choose to either get the second dose during pregnancy or wait to get the second dose until after you have had your baby. Many individuals who have already had the first dose may choose to get the second dose so they will become immune during pregnancy. The American College of Obstetricians and Gynecologists has convened an expert panel which recommends completing the vaccine course once it is initiated to receive the most effective and timely immunity.

  • I am planning pregnancy in the near future. Should I get vaccinated now or wait?

    The COVID-19 vaccines are not believed to affect your future fertility. Getting vaccinated before you get pregnant may prevent COVID-19 during pregnancy. It can also avoid the need for vaccination during pregnancy.


  • Can children get the vaccine?

    The Pfizer vaccine is approved for youth ages 12 and older. The Johnson & Johnson and Moderna vaccines are approved for people 18 years of age and older. The initial trials of these vaccines were limited to these age ranges and did not include younger individuals.

    Eligible patients 12–17 years old need a waiver signed by a parent to receive a Pfizer vaccine at a Mass General Brigham location.

  • When will children 11 and younger be able to get a COVID-19 vaccine?

    We do not know when one or more of the vaccines might be approved for this age group. 

    Children’s and adults’ immune systems are different and can produce different immune responses to vaccines. The vaccines need to be studied in children 11 and younger to make sure they are safe and that they work. There are currently several COVID-19 vaccine trials for pediatric patients. Once there is data, the vaccines will go through the same U.S. Food and Drug Administration (FDA) review process. The vaccines will be approved if the data shows they are safe and effective. It will likely take several months. 

  • Will children be vaccinated before the start of the 2021-22 school year?

    The Pfizer vaccine is currently approved for children age 12-17. As these vaccines are not yet approved for people younger than 12 years old, it is unlikely most young children will be vaccinated by the start of the coming school year. Teens and middle-grade children aged 12 -17 years may be vaccinated by the beginning of the school year. See more information on the CDC website.

Patients with cancer

Updated July 16, 2021