Frequently Asked Questions (FAQs) About the COVID-19 Vaccines

Based on research, it is likely that COVID-19 vaccines will prevent people from getting and spreading the virus.

Both the Pfizer-BioNtech and Moderna vaccines are showing about 95 percent efficacy in their preliminary reviews. This means people who received these vaccines in clinical trials had a 95 percent lower risk of getting COVID than people in the trial’s control group who did not receive a vaccine. The Johnson & Johnson vaccine showed 72 percent efficacy in U.S. clinical trials.

The clinical trials showed that all three vaccines were 100 percent effective at preventing hospitalizations and deaths from COVID.

The research so far shows that the vaccines are safe and effective.

We think that having COVID-19 may protect you from getting it again, but we are unsure how long. Some patients have had COVID more than once. It is recommended that people who have had COVID still get the vaccine.

It is too soon to know how long a vaccine will last. It is currently being researched. Of the people who have received the vaccine, we know that they have been protected from COVID-19 for at least 4 months.

It is impossible for the Pfizer-BioNTech, Moderna or Johnson & Johnson vaccines to give you COVID-19. None of the vaccines contain any live virus. Vaccines prime your immune system to recognize and fight off a disease, but they don’t actually cause an infection.

Learn about the types of COVID vaccines that are available or are in development

No, the COVID vaccines do not change or interact with your DNA in any way. The mRNA never goes into the nucleus – the part of the cell contains all of your own DNA and instructions – so it is impossible for it to alter your DNA.

Read more myths and facts about the COVID vaccine

The Moderna and Pfizer-BioNTech are mRNA vaccines that use tiny parts called messenger RNA (mRNA) carried in very tiny lipid particles. The Moderna and Pfizer-BioNTech vaccines differ in the way the mRNA is built or the way the lipids are used. The two vaccines are also stored in different ways, but each requires two doses.

The Johnson & Johnson vaccine is a vector vaccine, which places genetic material from the COVID-19 virus inside a weakened version of the adenovirus that cannot cause illness. Adenoviruses are very common viruses that usually cause colds. The Johnson & Johnson vaccine requires a single dose.

Learn more about the types of COVID vaccines that are available or are in development

The COVID vaccines prevent or lessen illness from the coronavirus. Both the Pfizer-BioNTech and Moderna vaccines have mRNA, which make the virus’ spike protein. This protein lets the virus attach to cells in our body. When we get the vaccine, we develop antibodies to the spike protein. This stops the virus from attaching to cells when exposed to the virus. Other parts of the body that prevent infection are made active by the vaccines to protect against future COVID-19 infection.

The Johnson & Johnson COVID-19 vaccine is a vector vaccine. Vector vaccines use genetic material from the COVID-19 virus that is placed inside a weakened version of another virus, such as the virus that causes the common cold.

The weakened virus is then injected into your body, delivering information from the COVID virus. That information instructs your cells to copy the spike protein that is unique to COVID-19 and create antibodies against the virus.

Vaccines for COVID-19 will start out being used under an Emergency Use Authorization (EUA) by the FDA. An EUA makes the vaccine available for public health emergencies. It means that the vaccine is available outside of a research study but is not yet approved. This is the usual first step for a new vaccine. The vaccine can continue to be used as long as people benefit from it. The research continues as it moves toward full approval.

The studies of vaccines included people ages 18 through 85 years old. It worked well for all ages. Studies are needed for people younger than 18 and pregnant women. More studies are going on or being planned. 

Yes, it is especially important for older adults to get the vaccine because they have the highest risk of being very sick or dying from COVID-19. 

Studies show that COVID vaccines are likely safe and will work for almost everyone. However, they cannot yet be used for children because those studies are not done.

If you are planning to become pregnant, you can receive the vaccine. The FDA also allows pregnant women to receive the vaccine. However, pregnant women were not studied in the vaccine trials, so there is not much information about the use of the vaccine among this group. If you are pregnant, we and the Society for Maternal-Fetal Medicine (SMFM) recommend that you discuss getting the vaccines with your provider. If you are breastfeeding, you can still get the vaccine and do not need to stop breastfeeding.

Yes, some people can get COVID again. It is also not known how long someone is protected from getting the virus again.

Yes, you should continue wearing masks, handwashing, and social distancing after getting the vaccine. This will help bring the pandemic under control. 

We know that the great majority of people, even those with severe allergies, have tolerated the COVID vaccine. People with allergies to environmental allergens (such as pollen), foods, latex, oral medications and stinging insects can receive the COVID vaccine. The vaccine does not contain egg, gelatin or latex.

CDC recommends not to receive a COVID vaccine if you had a severe or immediate allergic reaction to any of the ingredients in the vaccine or anaphylaxis (a severe allergic reaction) to the first dose of an mRNA vaccine. If you have a history of an immediate allergic reaction to polyethylene glycol (also known as PEG), or to polysorbate, you should not receive the vaccine.

If you have questions about if you should receive the vaccine, please talk to your health care provider.

Polyethylene glycol (PEG) is a common ingredient in a wide variety of vaccines and FDA-approved medications. It is found in the colonoscopy preparation, Golytely, in the constipation treatment, MiraLax, as well as in IV medications such as PEGylated medications. It is also in a steroid injection, Depo Medrol (methylprednisolone acetate). Reactions to PEG are rare, but anaphylaxis has been reported. Polysorbate is not an ingredient in either of the mRNA COVID-19 vaccines (Pfizer and Moderna), but it is closely related to PEG. The Johnson & Johnson vaccine contains polysorbate.

According to CDC guidelines, you may not be eligible to get the mRNA vaccine (or a second dose of the vaccine) if you have experienced any of the following allergic reactions.

• Severe allergic reaction (e.g., anaphylaxis) after a previous dose of an mRNA COVID-19 vaccine or any of its components
• Immediate allergic reaction of any severity to a previous dose of an mRNA COVID-19 vaccine or any of its components
• Immediate allergic reaction of any severity to polysorbate
• A history of an allergic reaction to an injectable medication

If you have experienced any of these reactions, please talk to your health care provider before getting a first or second dose of the vaccine.

If you decide to get the vaccine at a Penn Medicine vaccination site, you will be asked some questions about your allergy history before the vaccination. If you have had anaphylaxis (a severe allergic reaction) due to any cause, the vaccination team will decide if you need longer monitoring, or if you need to see your primary provider or allergy doctor before vaccination particularly if you report a history of an allergy to an injectable medication.

There are safeguards in place at Penn Medicine in case anyone experiences an allergic reaction to the vaccine. Everyone is monitored immediately after they receive the shot:

• At least 30 minutes for people who have a history of severe allergic reactions
• At least 15 minutes for all other individuals

We have a virtual urgent care service, called Penn Medicine OnDemand, which you can use as a resource at any time if you develop a reaction that concerns you.

If you received the COVID vaccine and developed a reaction within 4 hours of being vaccinated, you should call Penn Medicine OnDemand at 215-615-2222. Not all reactions are truly allergic reactions; a provider will first get information about your reaction and decide how to best manage it.

If you have severe symptoms with wheezing, throat tightness, nausea and hives, seek emergency care.

It is common to experience a reaction (or, side effect that is not considered allergic) to the vaccine. Side effects include fever, chills, muscle aches, headache and soreness at the injection site. These symptoms commonly begin happening at any time point after receiving the shot and typically last 2 to 3 days. If symptoms persist longer or you develop a high fever, please call Penn Medicine OnDemand.

It is common for people to have mild symptoms – such as tiredness, headache, muscle pain, chills, fever, nausea, and redness or soreness around the injection site – between 24 and 48 hours after receiving the Johnson & Johnson COVID vaccine.

If you recently received the J&J vaccine, you will most likely not experience any serious, adverse effects. If you develop severe headache, abdominal pain, leg pain or shortness of breath within three weeks of being vaccinated with the J&J vaccine, you should contact your doctor immediately or go to the nearest hospital emergency department. Make sure you tell the health care provider that you received the J&J vaccine.

Health care providers are asked to report adverse events to the Vaccine Adverse Event Reporting System.