Vaccine Safety FAQ


Is the vaccine safe?

The data from clinical trials indicate that the Janssen, Moderna, Novavax, and Pfizer-BioNTech vaccines are safe. All vaccines have undergone extensive clinical trials that tested for safety and efficacy before being submitted to the FDA for Emergency Use Authorization or approval. In addition, a significant body of real-world evidence has been collected and evaluated. To learn more about each vaccine, please see the vaccine fact sheets.

What are the common side effects?

For the most up-to-date information about side effects, please see the vaccine fact sheets ​​​​​.

Does the COVID vaccine cause inflammation in the heart?

Rare cases of inflammation of the heart muscle (myocarditis) and inflammation of the lining surrounding the heart (pericarditis) have been reported with the Pfizer-BioNTech and Moderna vaccines. These have typically occurred in males aged 12 to 29 years within a few days after receiving the second dose of vaccine. Most patients have required hospitalization with resolution of their acute symptoms. Patients have returned to their normal daily activities after receiving treatment for their acute symptoms. The benefits of the vaccine in preventing severe COVID-19 and hospitalizations outweigh the rare risk of myocarditis or pericarditis.

Does the COVID vaccine cause Guillain-Barré syndrome?

Rare cases of Guillain-Barré syndrome (GBS) have been reported in patients who received Johnson & Johnson's Janssen vaccine. GBS is an neurologic disorder in which the immune system damages nerve cells, which can result in muscle weakness or paralysis. Symptoms of GBS typically develop within 42 days of vaccination. The first symptom is often numbness of tingling of the hands and feet.

Most patients fully recover from GBS. To date, only 100 cases have been identified among 12.5 million vaccine recipients. Of those cases, 95 were considered serious and required hospitalization; 1 case resulted in death. Each year in the U.S., an estimated 3,000 to 6,000 people will develop GBS that was triggered by a viral or bacterial infection such as COVID-19. The benefits of the vaccine in preventing severe COVID-19 and hospitalizations outweigh the rare risk of GBS.

To date, the FDA has not seen a statistical increase in GBS inpatients who have received the Moderna or Pfizer-BioNTech vaccines.

Does the COVID vaccine cause blood clots?

On April 13, 2021, the FDA issued a pause on the Janssen vaccine to investigate reports of rare blood clotting disorders occurring after vaccination in women ages 18 to 48. The safety of the Janssen vaccine was affirmed and use resumed on April 23, 2021. The occurrence of blood clots was found to be extremely rare, with a slightly increased risk in women younger than 50 years of age. According to the Centers for Disease Control and Prevention (CDC), the likelihood of developing a blood clot after the Janssen COVID-19 vaccine is 4 cases per million doses. Blood clots have not been associated with the Pfizer-BioNTech or Moderna vaccines.

It is also important to note that COVID-19 itself can cause the body to develop blood clots in the brain 8 to 10 times more than receiving a COVID-19 vaccine. Approximately 20% of ICU patients who are admitted with COVID-19 have developed blood clots.

The cause of blood clots appears to be similar to a disorder called heparin-induced thrombocytopenia (HIT), an immune reaction to a blood thinner, heparin, commonly used in hospitalized patients. HIT decreases platelet levels and may cause blood clots. Patients who have a HIT within the past 30 days or other immune conditions that causes low platelets should receive either the Pfizer-BioNTech or Moderna vaccine instead. Patients with a history of blood clots or other conditions that may cause blood clotting that is not triggered by heparin or the immune system may receive any FDA-authorized COVID-19 vaccine, including the Janssen vaccine.

For more information, read the Center for Disease Control and Prevention's (CDC's) Interim Clinical Considerations for Use of COVID-10 Vaccines.

What if I have a reaction, side effect, or an adverse event?

If you experience any of the following severe allergic reactions, call 911 or go to your nearest hospital.

  • Difficulty breathing or wheezing
  • Drop in blood pressure
  • Swelling of the tongue or throat
  • Generalized rash or hives

If you believe you are having an adverse reaction, you should contact your healthcare provider and seek medical attention immediately. Adverse events following vaccination should be reported through the Vaccine Adverse Event Reporting System (VAERS) (1-800-822-7967 or through their website).

Please note: Dartmouth Hitchcock Medical Center and Clinics employees should follow the guidance outlined in the employee frequently asked questions found on the employee intranet.

The CDC has a new smartphone-based tool called v-safe to check in with people about side effects after they receive a COVID-19 vaccine. When you receive your vaccine, you should also receive a v-safe information sheet telling you how to enroll in v-safe. If you enroll, you will receive regular text messages directing you to surveys where you can report any problems or adverse reactions you have after receiving a COVID-19 vaccine.

Is the COVID-19 vaccine a live vaccine?

No, the Janssen, Moderna, Novavax, and Pfizer-BioNTech COVID-19 vaccines do not contain any live virus.

  • The Janssen vaccine uses a small piece of DNA protected by a harmless adenovirus to deliver the instructions for making a protein from the COVID-19 virus.
  • The Modern and Pfizer-BioNTech vaccines contain a very small piece of mRNA that gives your body instructions on how to make the "spike protein" located on the COVID-19 surface. Once this protein is made, it tells the body to make antibodies to fight the COVID-19 virus.
  • The Novavax vaccine uses harmless pieces of proteins of the virus that causes COVID-19. These proteins are pieces of what is often called the "spike protein." After vaccination, the body creates an immune response to these protein pieces. This response helps protect you from getting sick with COVID-19 in the future.

Can I receive the COVID-19 vaccine if I am pregnant or breastfeeding?

Pregnant and recently pregnant people with COVID-19 are at increased risk of severe illness, hospitalization, or death. Additionally, pregnancies affected by COVID-19 are at increased risk for preterm birth and stillbirths as well as other complications.

An analysis of VAERS and v-safe registry data has not identified any vaccine safety concerns with pregnant people or their infants. Additional safety research is underway. Available data show the vaccines are effective in pregnant people and indicate the benefits of the vaccine outweigh the risks of COVID-19.

Recent studies have also shown that antibodies produced after COVID-19 vaccination during pregnancy are transferred to the newborn, and COVID-19 vaccination of people who are pregnant reduces the risk of COVID-19 hospitalization in infants younger than 6 months.

We recommend that you refer to the vaccine fact sheets and recommendations from the American College of Obstetricians and Gynecologists (ACOG). Pregnant and lactating women may also contact their health care provider to discuss the current information available and each women's individual circumstance before making a decision about receiving the vaccination.

Please note: Women who are vaccinated with the Moderna COVID-19 vaccine during pregnancy are encouraged to enroll in the Moderna registry by calling 1-866-663-3762.

For more information, please see our Pregnancy and Breastfeeding FAQ

Can I receive the COVID-19 vaccine if I have had a severe allergic reaction to another vaccine?

If you have had a severe allergic reaction after a previous dose of this vaccine, or if you have had a severe allergic reaction to any ingredient in the vaccine, the Emergency Use Authorization Fact Sheet states that you should not receive a vaccine of the same type that you initially received.

We recommend that individuals with a history of anaphylaxis (severe, potentially life-threatening allergic reaction) consult their healthcare provider on making the decision as to whether or not to be vaccinated. Individuals who reacted to an initial dose of a COVID-19 vaccine should consult an allergist as they may still be eligible for a COVID-19 vaccine of a different type.

For more information about allergic reactions, please see the vaccine fact sheets.

Does the COVID-19 vaccine interfere with mammogram screenings?

Any recent vaccination—including those that you may receive, or have received, in the past for the flu, shingles and now for COVID-19—can cause the lymph nodes in the armpit on the injected side to become temporarily enlarged as part of the normal immune response to the vaccine. This lymph node enlargement may show up as an abnormality on the mammogram. If that were to happen, we would then recommend additional imaging. Most of the time, however, there is no observable change noted on the mammogram. At your mammogram appointment, the technologist will ask you if you received a vaccine in the arm in the last 2 months.

Please do not delay your mammogram screening. The Society of Breast Imaging does not recommend a delay between scheduling your vaccine and mammogram screening.

As always, if you have a sign or symptom of breast cancer you should not delay seeking treatment under any circumstances.

Can I get my flu shot at the same time as my COVID-19 vaccine?

The CDC has said that COVID-19 vaccines and other vaccines can be administered at the same time. This includes receiving both the COVID-19 vaccine and other vaccines, like the flu shot, on the same day. However, if you have a history of reaction to the flu shot, talk to your provider first.

Should children be getting the COVID-19 vaccine?

The CDC's advisory committee has advised that the Moderna and Pfizer-BioNTech COVID-19 vaccines are safe and effective for people aged 6 months and older.

Despite the fact that many children experience less severe illness from COVID-19, some children suffer serious complications. There is also growing evidence that as many as 25% of children suffer from symptoms such as respiratory issues, fatigue, and stomach problems, for weeks or months (sometimes referred to as “long haul” disease). And, just like adults, children who have few or no symptoms can still transmit the virus to others.

The surest way to protect children and our communities from the harmful effects of COVID-19 is to get the vaccination.

For more information, please see our Pediatric and Adolescent COVID-19 Vaccine FAQ

Is it safe to get a COVID-19 vaccine if I have an underlying medical condition?

Yes. COVID-19 vaccination is especially important for people with underlying health conditions like immune system issues, heart disease, lung disease, diabetes, and obesity, as these increase the risks and severity if you were to get COVID-19.

Patients with a history of myocarditis (inflammation of the heart muscle) or pericarditis (inflammation of the lining surrounding the heart) may receive the COVID-19 vaccine after the episode has completely resolved (no symptoms and no evidence of ongoing heart inflammation).

Should I get a COVID-19 vaccine if I've had multisystem inflammatory syndrome in children (MIS-C) or adults (MIS-A)?

It is unknown whether patients with MIS-C or MIS-A are at risk of developing the syndrome again following reinfection or in response to vaccination. Patients with MIS-C or MIS-A may choose to be vaccinated after considering clinical recovery, personal risk for severe COVID-19, and the unknown safety data for using vaccines in this population. A conversation with your health care provider may assist in your decision, but it is not required. Patients may also opt to defer up to 90 days from the date of diagnosis with MIS-C or MIS-A.

For more information, please visit the CDC's Multisystem Inflammatory Syndrome (MIS-C) page.

I recently received a dermal filler. Is it safe to get the COVID-19 vaccine?

Infrequently, people who have received dermal fillers might experience swelling at or near the site of filler injection (usually face or lips) following the administration of a dose of an mRNA COVID-19 vaccine. FDA-authorized COVID-19 vaccines can be administered to people who have received injectable dermal fillers who have no contraindications or precautions for vaccination; however, these people should contact their health care provider for evaluation if they experience swelling at or near a dermal filler site following vaccination. The swelling is usually temporary and resolves with medication such as corticosteroid.

Where can I learn more about the vaccines?

You can find additional information about effectiveness on the vaccine fact sheets: