Coronavirus Information and Resources

COVID-19 Vaccine Frequently Asked Questions

Last revised 12/21/20


A vaccine is a chemical preparation that stimulates your body’s immune system to recognize and control of a virus, bacterium, or other microbe. After vaccination, your body will be better able to protect you against that microbe in the future. 

The Food and Drug Administration (FDA) has granted Emergency Use Authorization to three COVID-19 vaccines – Pfizer-BioNTech, Moderna, and J&J/Janssen. 

Pfizer-BioNTech and Moderna are messenger RNA (mRNA) vaccines. They are made in the lab using components of messenger RNA (mRNA). All living things make mRNA in order to make the proteins in the body. The vaccines use mRNA that can tell and give a message to our cells to make a virus protein, called Spike protein, that is essential for the novel coronavirus to invade our cells and make us sick. In order to help our cells do this, the mRNA is coated with tiny oil droplets that protect the mRNA until it does its job. Once this Spike protein is made and our immune system “sees” the protein, this triggers an immune response to the protein that prepares us to respond (respond by making “antibodies”) if our body sees the novel coronavirus at some point in the future. After the protein piece is made, the cell breaks down the message with the instructions and gets rid of it. mRNA vaccines do not use live virus. The mRNA never enters the nucleus of the cell, which is where DNA is confined. Cells break down and get rid of the mRNA soon after using the instructions.

The J&J/Janssen vaccine is based on a different technology to teach cells how to fight infection with SARS-Co-V-2, the virus that causes COVID. It uses a viral vector, a modified version of a different virus (the vector), to deliver the important instructions to our cells. The vector (not the virus that causes COVID-19, but a different, harmless virus) will enter a cell in our body and then use the cell’s machinery to produce a harmless piece of the virus that causes COVID-19. This piece is known as a spike protein, and it is only found on the surface of the virus that causes COVID-19. The cell displays the spike protein on its surface, and our immune system recognizes it doesn’t belong there. This triggers our immune system to begin producing antibodies and activating other immune cells to fight off what it thinks is an infection. At the end of the process, our bodies have learned how to protect us against future infection with the virus that causes COVID-19.

The Pfizer and Moderna vaccines require two shots, while the J&J/Janssen is a single shot. 

Antibodies are also proteins. They function as soldiers that protect the body against harmful particles like COVID-19.

According to the Centers for Disease Control and Prevention, all COVID-19 vaccines currently available in the United States are effective at preventing COVID-19, as seen in clinical trial settings.

Research provides growing evidence that mRNA COVID-19 vaccines offer similar protection in real-world conditions. Results of a recent real-world conditions study of health care personnel, first responders and essential personnel showed those who were fully vaccinated were 90% less likely to get infected.

The J&J/Janssen vaccine was 66.3% effective in clinical trials (efficacy) at preventing laboratory-confirmed COVID-19 illness in people who had no evidence of prior infection two weeks after receiving the vaccine. People had the most protection two weeks after getting vaccinated. The vaccine was very effective in preventing severe COVID-19 in these clinical trials.

Some people who are fully vaccinated against COVID-19 will still get sick because no vaccine is 100% effective. Experts continue to monitor and evaluate how often this occurs, how severe their illness is, and how likely a vaccinated person is to spread COVID-19 to others.

The FDA and CDC have authorized the use of the Pfizer vaccine for individuals 12 years and older. The FDA and CDC have authorized the use of the Moderna and J&J/Janssen vaccines for those age 18 and older. The vaccines are intended for the general public, with very few exceptions. People whose jobs exposed them to others on a regular basis should get the vaccine. People who are older and/or have underlying illnesses, such as diabetes, high blood pressure, and obesity, are especially encouraged to get vaccinated. Certain ethnic groups, particularly African-Americans, Latinx, Native Americans, have high rates of severe COVID-19 and death.

In the US, all eligible individuals are encouraged to get a COVID-19 vaccine unless there are medical reasons not to do so. Children may be added to this as well as we get more information on how vaccines work in them.

At the moment, children under age of 16 have not been studied and are therefore not part of this vaccination program. Studies are ongoing to evaluate safety and efficacy in children.

Those with a history of severe allergic reaction (e.g. anaphylaxis) to any component of the Pfizer-BioNTech vaccine should not get this vaccine. 

Persons with a history of severe allergic reaction to another type of vaccine or injectable medication have been cautioned to weigh risks and benefits, and if vaccinated, would require a longer observation period (30 minutes instead of 15 minutes) following their injection. 

There is not much data for people who are on immunosuppressive medications, have HIV, etc. These people are at higher risk of getting severe COVID19 virus infection. Since the Pfizer and Moderna vaccines do not have the virus, if there is no other contraindication, these vaccines can be administered. The J&J/Janssen vaccine does have a live virus, but there are no restrictions for immunocompromised patients. The J & J/Janssen vaccine does have a live virus, but there are no restrictions for immunocompromised patients.

Vaccine protection may be less for those with immunocompromising conditions or drugs. Therefore, you should still practice masking and physical distancing as before until there are more data.

We recommend that you discuss with your provider to make an informed decision.

Yes. No vaccine is 100% effective. However, even if you get COVID-19, studies have shown that you will have a milder case of it. According to the studies, these vaccines are highly effective.

A growing body of evidence suggests that fully vaccinated people are less likely to have asymptomatic infection and potentially less likely to transmit SARS-CoV-2 to others. However, further investigation is ongoing, and it is still very important that we continue to follow current prevention guidance – mask-wearing, handwashing, and social distancing—even after we have been vaccinated. 

mRNA technologies have been studied for more than a decade. The mRNA vaccines have gone through the same rigorous process that other vaccines. medicines, or devices must go through. No phases of this process have been skipped. The quick authorization for these vaccines has much more to do with the Federal government funding the mass production of these vaccines much earlier than usual. 

The mRNA vaccines have been quite safe as tested so far. To this moment, some people getting vaccinated have had fever, fatigue, and pain at injection site for a day or two after the injection. A few individuals with history of severe allergies have had allergic reactions to the Pfizer vaccine. No such reactions have been seen with the other vaccine so far.  

On April 13, 2021, the CDC and FDA recommended a pause in the use of the J & J COVID vaccine, which uses a different technology than the mRNA vaccines, due to a small number of cases of a rare type of blood clot in women reported after they received the J&J/Janssen COVID-19 vaccine. The FDA and the CDC Advisory Committee on Immunization Practices (ACIP) have reviewed available information on these cases.

The ACIP concluded that the benefits of this vaccine far outweigh the risk of this very rare complication. Following the ACIP recommendation, the CDC and FDA recommended that use of the J&J/Janssen COVID-19 vaccine resume in the United States, effective April 23, 2021. They have also provided guidance to health care providers in the identification and treatment of these rare complications.

In particular, women younger than 50 years old should be aware of the rare risk of blood clots with low platelets after vaccination, and that other COVID-19 vaccines are available where this risk has not been seen. If you received a J&J/Janssen vaccine, here is what you need to know. Read the CDC/FDA statement. Individuals who get this rare side effect will develop new onset of headaches, abdominal pain and/or chest pain between 6-21 days after vaccination. If you develop these, contact your provider for evaluation. 

The most common side effect is soreness in the arm you got the vaccine, as most people have a sore arm after getting the vaccine. Sometimes the arm can also get a little red and swollen where the vaccine was given. 

After that, feeling tired, having body aches, and headaches are the most common side effects of the vaccine. These side effects are more likely to happen after the second dose of the vaccine, although they can happen after the first dose. These most common side effects can happen with many vaccines, and are a sign they are working in our bodies to activate our immune system, which is why they happen more with the second dose of the vaccine.

Less commonly, some people who received the vaccine had stomachache, nausea, vomiting, and diarrhea, and a few people had chills and sometimes a fever. 

We do not expect that there will be long-term side effects from the vaccines, but at the moment we do not have long-term safety data. 

No. The technologies used to produce these vaccines do not contain COVID-19 virus. 

Based upon results of a study of the safety of mRNA vaccines in more than 35,000 pregnant women that reported no safety concerns were observed for women or their babies, the Centers for Disease Control and Prevention now recommends that pregnant women receive the COVID-19 vaccine.

The American College of Obstetricians and Gynecologists recommends that COVID-19 vaccines should not be withheld from pregnant individuals. Individuals considering a COVID-19 vaccine should have access to available information about the safety and efficacy of the vaccine, including information about data that are not available. A conversation between the patient and their clinical team may assist with decisions regarding the use of vaccines approved under EUA for the prevention of COVID-19 by pregnant patients.

The American College of Obstetricians and Gynecologists released the following statement after a pause in the use of the J & J/Janssen COVID vaccine was recommended due to rare blood clots reported in six women after receiving the J & J/Janssen vaccine. “At this time, there is no clear phenotype of women who are more or less likely to experience this rare complication. However, until there is a better understanding of the frequency and impact of this finding, it will be important to encourage pregnant and postpartum women who wish to be vaccinated to receive the mRNA vaccines: Pfizer or Moderna."  

The American College of Obstetricians and Gynecologists advises that COVID-19 vaccines should be offered to lactating individuals similar to non-lactating individuals. 

The current vaccine is not approved for children under 16 years of age. Studies to evaluate safety and efficacy are ongoing in children.

Pfizer has requested that its Emergency Use Authorization be expanded to include 12-15-year-olds. 

The Pfizer-BioNTech and Moderna vaccines both include a two-injection series. It is important to complete the two doses in order to maximize your chances of protection. For the Pfizer vaccine, the second dose should be administered 3 weeks (21 days with a grace period of 4 days, 17-21 days) after the first. If more than three weeks pass since the first vaccine is received, the second dose should be given at the earliest opportunity. There is no need to repeat any doses. The Moderna vaccine’s second dose should be administered 28 days after the first.

The J & J/Janssen vaccine is a one-dose vaccine.

Yes. If you are currently not infected and your quarantine period is over, you can get the vaccine. According to studies, having COVID-19 infection does not give you lifelong protection against COVID-19.

No. If you actively have COVID-19 or are currently sick, it is recommended to delay taking the vaccine until your symptoms resolve and the recommended quarantine/isolation period is completed. Studies have shown that someone who gets infected, does not get reinfected for 3 months/90 days. If desired, vaccine can be deferred for 3 months.

Individuals who recover from COVID-19 will have antibodies against a number of viral proteins, including the spike protein.

These vaccines are causing the body to make antibodies against the spike protein. If you have had COVID-19, these vaccines will boost your antibodies to the spike protein but not to other viral proteins.

COVID-19 antibody tests detect a number of antibodies against COVID-19. Some tests only detect antibodies to the spike protein. If you had COVID-19 or if you got the vaccine, you would be positive for these antibodies. Some tests detect antibodies to other COVID-19 proteins. If you have had COVID-19, you could be positive for these antibodies. If you just had the vaccine without infection, you would test negative for these antibodies. We currently do not routinely test for antibodies.

Since the vaccines do not have the COVID-19 virus, they should not interfere with the PCR testing.

Absolutely yes, at this time. Although the evolving data are promising, we do not know yet for how long these vaccines will be protective and will produce protective antibodies. In addition, we do not know if you can still get infected without symptoms and pass the virus to others who are susceptible. Until we have more data and more people get vaccinated, we all should continue practicing the public health recommendations:

  • wearing a mask
  • physical distancing - staying 6 feet away as much as possible
  • handwashing
  • avoid crowds unless you know that everyone is vaccinated

According to the clinical studies, it may take up to 1 to 2 weeks after receiving the second dose for your body to produce an effective immune response.

According to CDC, you are maximally protected two weeks after completing the vaccination series.

If you had a high-risk exposure to someone with COVID-19 (close together without masks for >15 minutes) in the 14 days prior to getting your vaccine, and you develop symptoms, you should consider getting tested for COVID-19. 

If you have symptoms that both the vaccine and COVID-19 cause (muscle aches, fatigue), and you received the vaccine in the last 2-3 days, it can be hard to tell if these are coming from a potential COVID-19 infection or the vaccine. If you feel overall well, don’t have any other concerning symptoms, and don’t have a fever, you likely do not need to be tested for COVID-19.

However, if you start to feel worse or develop other symptoms (i.e. cough, difficulty breathing, runny nose, sore throat, loss of taste or smell) you should likely be tested as these are not common side effects of the vaccine. If you have a fever, you should also consider getting a COVID-19 test.

Since the vaccines have not been around for very long, we do not know how long they will protect people. Research is ongoing, and Pfizer’s most recent results show that its vaccine is still going strong. On April 1, Pfizer announced the results of an analysis of six months’ worth of data on its vaccine against COVID-19. The study found that the vaccine remains 91.3% effective against COVID-19. The vaccine was 100% effective against severe disease as defined by the U.S. Centers for Disease Control and Prevention (CDC), and 95.3% effective against severe COVID-19 as defined by the U.S. Food and Drug Administration (FDA). Pfizer began the phase 3 clinical trial on its vaccine on July 27, 2020, and will continue to follow participants for the next two years following their second dose.

An interim study of the Moderna vaccine published April 6, showed similar results. Protection persisted through six months, and ongoing studies are monitoring immune responses beyond 6 months.


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