COVID-19 Vaccine Frequently Asked Questions

The following responses were provided by University of Wisconsin-Madison public health experts Ajay Sethi, Ph.D., MHS, Associate Professor in Population Health Sciences and Faculty Director of the Master of Public Health Program and Devlin Cole, MD, MPH, Preventative Medicine Resident, School of Medicine and Public Health.

Last updated Nov. 9, 2021.

Vaccine Technology and Development

How can the vaccine be safe if it was made so quickly?

The U.S. Food and Drug Administration (FDA) has in place a process that manufacturers and researchers must follow to assure that vaccines and treatments authorized for use in people are safe. In the development and testing of COVID-19 vaccines, none of these steps were skipped and included animal studies prior to Phase I, II, and III clinical trials in human beings. Since December 2020, tens of millions of doses have been administered to Americans. The nation’s Vaccine Adverse Events Reporting System (VAERS) is used to monitor the safety of COVID-19 vaccines as they are rolled out across the country. To date the Pfizer and Moderna vaccines have been found to be safe, and the risk of severe reaction is outweighed by the protection it offers against the virus that causes COVID-19. For further reading about the safety of COVID-19 vaccines, this news article in Nature is helpful.

Who was included in the trials?

For the Pfizer vaccine trial, adults 16 years of age or older who were healthy or had stable chronic medical conditions, including but not limited to human immunodeficiency virus (HIV), hepatitis B virus, or hepatitis C virus infection, were eligible for participation in the trial. Individuals with a medical history of COVID-19, treatment with immunosuppressive therapy, or diagnosis with an immunocompromising condition were excluded. More details can be found in the New England Journal of Medicine article here.

For the Moderna vaccine trial, eligible participants were persons 18 years of age or older with no known history of SARS-CoV-2 infection and with locations or circumstances that put them at an appreciable risk of SARS-CoV-2 infection, a high risk of severe Covid-19, or both. More details can be found in the New England Journal of Medicine here.

Were participants in the trials exposed to COVID-19? If not, how were the vaccines challenged?

No, participants were not intentionally exposed (i.e., challenged) to SARS-CoV-2 in the trial. After participants were given at random either the vaccine or placebo, they were followed over time for development of COVID-19 symptoms. Anyone who developed symptoms were tested for SARS-CoV-2.

Manufacturers claim that their vaccines are 90% or 95% efficacious. What do these numbers mean in terms of vaccine effectiveness?

How well the vaccines work in the “real-world” (i.e., effectiveness) will be determined in 2021. There is hope that they will greatly reduce the occurrence of COVID-19 illness, hospitalizations, and deaths in our society as the high-level efficacy estimated from the clinical trials indicate, but that is to be determined.

How long are the vaccines effective? Will people need to get the vaccine annually like the flu shot?

It is unknown right now when immunity induced by the vaccines wanes to a level that a booster is indicated. The need to protect people against any new variants and/or waning immunity will be reasons for re-immunizing or boosting individuals.

Are the vaccines effective against the new variants? How concerned should we be about these mutations?

The new variants are concerning because they are more infectious. Fortunately, individuals can employ the same mitigation strategies to protect themselves against them (mask use, physical distance, hand washing, avoiding crowded environments), but practicing these precautions will need to be adopted by even more people in order to keep the new variants from becoming the dominant strains circulating. Studies show that both the Pfizer and Moderna vaccines are effective at protecting immunized individuals against the new variants.

Can mRNA vaccines change or mutate our own DNA?

No, this concern is a product of misinformation that spreads online and not reflective of how the mRNA vaccines actually work. mRNA is rather fragile and degrades quickly; hence, the need to store vaccine vials at very cold temperatures. Once injected into the arm, the mRNA finds ribosomes in the cell is translated into the spike protein. The mRNA degrades and one’s immune system begins to learn how to develop antibodies and other types of immunity to the spike protein. That immunity is what gives one protection against the SARS-CoV-2 virus if infected at a later time.

What are examples of mRNA-based vaccinations/therapies used in the past?

Since 2013, Moderna and Curevac are two companies that have been testing, with FDA approval, mRNA vaccines. They have been working on vaccines for influenza, metapneumovirus, parainfluenza virus, zika, and others.

 Vaccine Distribution

How are decisions being made about who is eligible to be vaccinated at both a national and state level?

At the Federal level, the Centers for Disease Control and Prevention (CDC) make allocation decisions based on recommendations from the Advisory Committee on Immunization Practices (ACIP). These ACIP meetings can be watched from the CDC website, and meeting materials are often posted after the meetings.

At the State level, the State Disaster Medical Advisory Committee (SDMAC) develops guidance and advises the Wisconsin Department of Health Services (DHS) Secretary.

Who is administering the vaccines?

Facilities with the capacity to vaccinate eligible populations can apply to the Wisconsin Department of Health Services for vaccinating entity approval. Currently, over 1,000 individual vaccinating entities have been authorized by the state. These range from individual doctor’s offices, to large hospitals, to local public health departments, pharmacies, employers, community-based vaccination clinics, and on-site vaccination clinics. You can visit to find a COVID-19 vaccine near you.

Will the vaccine be required or optional?

The COVID-19 vaccines available in the United States have an Emergency Use Authorization from the FDA. It is currently being explored in legal venues the ability of an employer to require this vaccination, when it is available. Even in the instance where the vaccine is available and required, employers will still have to navigate medical and personal belief exemptions (see the document below). These situations will likely become more frequent when the vaccines have full FDA approval.

For more information, please refer to section K of the EEOC document.

Is the vaccine safe and effective for pregnant, breastfeeding women and women of reproductive age?

There is no population level data on the safety of the COVID-19 vaccine in pregnant and breastfeeding women. Based on current knowledge, experts believe COVID-19 vaccines are safe for pregnant people, infants, and fetuses. Individual risk and benefit assessment needs to be performed by a woman’s primary care physician, but neither pregnancy nor breastfeeding status is a contraindication to getting this vaccine. View this factsheet from DHS for more information. (link:

This vaccine is safe for women of childbearing age. Women of childbearing age were included in the clinical trials and no effects on reproduction were seen. There is no evidence that the vaccine impacts fertility.

Is the COVID-19 vaccine available for children?

The CDC recommends that children and adolescents age 5 and older get a COVID-19 vaccine. The Pfizer COVID-19 vaccine is authorized for children and adolescents age 5 and up, as a 2-dose series taken 3 weeks apart. The dose for children aged 5-11 is one-third of the dosage of the vaccine for older adolescents and adults. For more information on vaccines for children and teens visit

Why should my child get the COVID-19 vaccine?

COVID-19 has become one of the top 10 causes of pediatric death, and tens of thousands of children and teens have been hospitalized with COVID-19. While children and adolescents are typically at lower risk than adults of becoming severely ill or hospitalized from COVID-19, it is still possible. Medical experts are also learning about the long-term effects of COVID-19 in children. Getting your child vaccinated helps to protect your child, your family, and your community. Find more COVID-19 resources for parents and guardians (

Is the COVID-19 vaccine safe for children?

Yes. Studies show that COVID-19 vaccines are safe and effective. Before being authorized for children, scientists and medical experts completed their review of safety and effectiveness data from clinical trials of thousands of children. The Pfizer COVID-19 vaccine was rigorously tested and reviewed, and over 11 million adolescents ages 12-17 have already safely received the COVID-19 vaccine. By getting vaccinated, your child will be protected from getting sick and reduce the chances of spreading the virus to others. Like adults, children may have some side effects after COVID-19 vaccination. These side effects may affect their ability to do daily activities, but they should go away in a few days. Learn more about the COVID-19 vaccine for kids ages 12 and older (

Receiving a Vaccine

Where and when can I get the vaccine?

DHS provides information about how to locate vaccine providers in your area. Visit to find a COVID-19 vaccine near you.

I have an underlying health condition, should I get the vaccine?

Consult with your primary doctor about your specific health condition and any concerns you have about receiving the vaccine. COVID-19 vaccines may be provided to people with underlying medical conditions as long as they have not had a severe or immediate allergic reaction to any of the ingredients in the vaccine. You can find more information about vaccine considerations for people with underlying medical conditions on the CDC’s website.

Can I choose which vaccine I receive?

You may be able to choose which vaccine you receive.  However, a vaccinating entity may only receive one type of vaccine. All currently authorized and recommended COVID-19 vaccines are safe and effective. The Pfizer COVID-19 vaccine is the only vaccine authorized for children 12-15 years.

What side effects should I expect? Are they worse after you receive your second dose?

Over 3/4 of people experience pain in their arm starting a few hours after the vaccination was given. This arm pain may be accompanied by redness and mild swelling. Be sure to keep moving your arm to increase the blood flow! Only about ⅓ of people experience fatigue and headache after the vaccine. About 10-15% of people will experience more severe side effects like fever and chills. Some people report feeling stronger side effects after the first dose, and some after the second. It is very individual.

Please keep in mind that most doctors recommend NOT taking over the counter medications BEFORE vaccination, in anticipation of feeling symptoms. This can decrease the effectiveness of the vaccine. However, AFTER the vaccine, taking over the counter pain medications, using ice and heat on aching muscles, and other self-care is strongly recommended. These symptoms, however, are not contagious, and are not at all an indication that you got COVID-19. You cannot get COVID-19 from the vaccine, as there is no live virus in the vaccine at all.

Are there any known side effects for people with chronic diseases?

The term “chronic disease” is very broad. So, in general, you can expect similar side effects to those described for the general population.

Immunosuppressed individuals were not included in the clinical trials, so population level data is not available. In fact, they may have decreased side effects due to a diminished ability of the immune system to mount a response. However, the side-effect monitoring system, V-Safe, does not distinguish by chronic disease, so the rates of side effects are for the general population.

Talk with your doctor if you have more concerns.

How do you address the unknown long-term side effects question?

The federal government is constantly monitoring for adverse events after vaccination through a number of surveillance mechanisms, used to assess safety of all vaccines, including the VAERS website.  All safety concerns are taken seriously, and thoroughly investigated to determine whether there is possible causation rather than the more typical coincidental association.  Vaccine manufacturers are required by FDA to continue monitoring all vaccine study participants as well as all vaccine recipients once the vaccines are approved, in what are typically called Phase 4 trials.  Ongoing monitoring is an important part of any FDA authorized or approved vaccine.  Short-term side effects are generally found within 1-7 days of receiving a vaccine, and there has never been a ‘long-term’ vaccine side effect that emerged more than a few months after administration of a vaccine. Thousands of people were initially vaccinated over a year ago, and no new long-term side effects have been detected.

Response provided by Dr. James H Conway, MD FAAP

Is it possible to test positive for COVID-19 after having received the vaccine?

Yes. The maximal immune response occurs about 2 weeks after the second vaccine. A positive test after vaccination could represent an infection that started before the vaccine was received, or that even with the immune response to the vaccine, the illness was still contracted. A few people do still get COVID-19, even after full vaccination (both vaccine brands will lower rates of COVID-19 illness by 94-95% in a fully vaccinated population, but 5% of the original rate of infection will still be observed).

If someone already had COVID-19, do they need to get vaccinated?

Yes. We currently estimate that immune protection from having COVID-19 lasts about 3 months. And reinfection has been found, especially with new strains circulating. It is recommended that anyone who has COVID-19 should still get vaccinated when they are part of the eligible population.

How long after having COVID-19 should someone wait to get vaccinated? What if it was a serious case of COVID-19?

Because the current estimate for immune protection from having COVID-19 is about 3 months, an individual could delay getting the vaccine for 90 days from their first day of symptoms. However, this is not required. Anecdotally, people who have very recently had COVID-19 are having significant side effects with the vaccine, so a small delay might help with comfort, though it does not affect the vaccine efficacy.

What do we know about COVID-19 transmission among individuals who have been vaccinated?

COVID-19 vaccines reduce the risk of people spreading the virus that causes COVID-19. If you are fully vaccinated you can resume activities you did before the pandemic. The vaccines will likely not prevent transmission 100% of the time.

If a person is vaccinated, do they still need to wear a mask and social distance?

No. Fully vaccinated people can resume activities without wearing a mask or physically distancing, except where required by federal, state, local, tribal, or territorial laws, rules, and regulations, including local business and workplace guidance. If you are fully vaccinated, you can resume activities that you did before the pandemic. You can read additional recommendations for fully vaccinated people here:

If a person is vaccinated and exposed to COVID-19, do they still need to quarantine?

CDC guidance does not require a vaccinated individual to quarantine after exposure if the exposure occurs at least two weeks after the second dose of vaccine. However, they should still monitor for symptoms of COVID-19 for 14 days following an exposure.

Should a person get a vaccine if they are on medication that weakens the immune system, like medication for rheumatoid arthritis or other autoimmune diseases?

 First and foremost, consult with the physician prescribing these medications. However, immune modulating medications are not contraindications for the COVID-19 vaccine, so many individuals are still choosing to get vaccinated in this instance.

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