What to know about the COVID-19 vaccine

Gloved hands holding COVID-19 vaccine

Each year, vaccines protect us from at least 20 diseases and save up to 3 million lives. When we get vaccinated, we aren’t just protecting ourselves, but also those around us. Some people are not able to get certain vaccines. They depend on the rest of us to get vaccinated to help protect them and reduce the spread of disease.

Thanks to emergency use authorization and approval from the U.S. Food and Drug Administration, we now have vaccines to protect us from COVID-19. Here is what you need to know about the COVID-19 vaccines, including how safe and effective they are, who should and should not receive them and when it will be your turn.

How was the COVID-19 vaccine developed so quickly?

Typically, it takes years to develop vaccines, assure their safety and effectiveness (known as efficacy), and then manufacture them on a mass scale. However, to quickly address the COVID-19 pandemic, the timeline was accelerated through national and international programs supporting the work of scientists around the globe, including teams here at the University of Chicago Medicine. The accelerated research and development process allowed scientists to perform many steps simultaneously rather than sequentially. The federal effort also provided funding to support the work of pharmaceutical companies to begin manufacturing vaccines before they are approved — allowing for quick distribution if a vaccine earns FDA authorization.

Additionally, the technology used to create this mRNA vaccine has been in development for decades. The COVID-19 pandemic provided an opportunity to put years of scientific study into practice. And, because of this technology, the virus did not have to be grown in a lab, which further accelerated the vaccine’s creation.

Who was included in the vaccine trials?

Scientists tested the vaccines during clinical trials to make sure each immunization met or exceeded established safety and efficacy thresholds. Trials began with small groups of people before expanding to include much larger numbers — tens of thousands — making sure to include a wide range of people from across the country and around the world. This includes people of different ages, races, sexes, and health conditions, including HIV, diabetes and lung disease. Scientists studied how well the vaccines worked when compared to a control group, which received a placebo version of the vaccine. Pharmaceutical companies will track clinical trial participants for up to two years after they received a vaccine to make sure they remain healthy.

How effective is the COVID-19 vaccine?

Vaccines developed by Pfizer/BioNTech and Moderna have had an independent interim analysis performed on their vaccines. The Pfizer/BioNTech vaccine was reported to be 95% effective after two doses, and 52% effective after the first dose alone. The Moderna vaccine was reported to be 94.1% effective after two doses. This is true for all groups of participants who were evaluated, regardless of age, weight or race.

How do scientists know the COVID-19 vaccine is effective?

During the COVID-19 clinical trials, scientists gave participants either the COVID-19 vaccine or a placebo, a harmless treatment that has no impact on the body, to compare the results. Scientists checked the participants to see if they had made antibodies that protected them from COVID-19. The researchers also measured the infection rates and compared them between the vaccine group and the placebo group. The participants who received the vaccine were significantly more likely to have antibodies and were significantly less likely to contract COVID-19 or get seriously ill from it than those who received the placebo.

How safe is the COVID-19 vaccine?

Only vaccines that meet standards for safety and efficacy are approved for emergency use by the FDA. Vaccines are assessed to see whether and how well they can protect people from SARS-CoV-2, the virus that causes COVID-19. Any approved COVID-19 vaccine is tested in a trial of at least 30,000 volunteers and reviewed to make sure it is safe. Like any medical therapy, getting vaccinated is accompanied by some degree of risk. However, the reported potential risks and side effects of a COVID-19 vaccine are substantially lower than the risks and side effects associated with contracting COVID-19.

What are the potential vaccine side effects?

All medical treatments have some degree of risk. For vaccines, that risk is typically small. Many vaccines have mild side effects, which usually range from soreness at the site of injection to a slight fever, body aches and a headache; some people have no reactions at all. However, it’s important to know that risks reported in connection with the COVID-19 vaccine are significantly lower — and less severe — than the risks associated with contracting COVID-19 itself.

After receiving the Pfizer/BioNTech vaccine, trial participants commonly felt injection site pain. That was followed by fatigue and a mild to moderate headache. Other reported side effects included fever, chills, muscle pain, joint pain and swollen lymph nodes. Side effects were more commonly seen in people between the ages of 18-55 than those who were 65-85. Side effects were also slightly more likely to occur after the second dose. They typically peaked within two days and were completely over within seven days.

Early data from Moderna’s clinical trial also showed typical mild to moderate side effects, such as headaches, fatigue, muscle aches, chills and injection site pain. Severe side effects included fatigue in 9.7% of participants, muscle pain in 8.9%, joint pain in 5.2%, and headache in 4.5%. Reactions typically occurred within one to two days of receiving the vaccine and were all resolved within seven days.

Does the COVID-19 vaccine cause Bell’s palsy?

Throughout the Moderna and Pfizer/BioNTech clinical trials, eight cases of Bell’s palsy — a type of rare, sudden muscle weakness in the face — were reported in total. Four of the cases were in the Pfizer vaccine group, three in the Moderna vaccine group, and one in the Moderna placebo group. The rate of Bell’s palsy incidence in the vaccine clinical trials was less than or equal to the rate of developing the condition in general. While there’s no evidence the cases were caused by the vaccine, they are considered an adverse event and will continue to be reported and monitored as a special interest adverse effect. 

Can the COVID-19 vaccine cause infertility or miscarriages?

No, the COVID-19 vaccine cannot cause infertility or miscarriages. Antibodies to COVID-19 spike protein – those developed both from getting the virus and from getting the vaccine – have not been linked to infertility. There has also been no increase in the risk of miscarriage in women who have had COVID-19 during pregnancy. The virus’ spike protein does not attach to the placenta and cause miscarriage. If you’re pregnant, trying to become pregnant, or breastfeeding, you can learn more about the COVID-19 vaccine and reproductive health in our Q&A with UChicago Medicine obstetricians and gynecologists.

Can you get a COVID-19 vaccine if you’re pregnant, planning to become pregnant, or breastfeeding?

The CDC has indicated that the vaccine may be administered to pregnant women and several professional societies have advocated for these individuals to be vaccinated. However, if you have questions or concerns, you should discuss with your healthcare provider. The CDC says those who are pregnant should weigh the following when deciding whether to get the vaccine:

  • Your individual risk of acquiring the virus (both to community transmission and occupation)
  • The potential damaging health outcomes of contracting COVID-19 while you’re pregnant
  • The side effects that you may experience after receiving the vaccine
  • The safety and efficacy data currently available

Learn more about what our panel of obstetrics and gynecology experts recommends to those pregnant, trying to get pregnant, or breastfeeding.

Can you get COVID-19 from the vaccine? Can it cause a false-positive test result?

No, it is not possible to get COVID-19 from this vaccine, and it won’t produce a positive COVID-19 test result. You may feel unwell after getting vaccinated, but this is a sign of your immune system starting to activate to protect you. However, you could still catch the virus after being immunized and before your body’s immune system has reached its full ability to fight the virus. In addition, much like the flu vaccine, COVID-19 vaccines are not 100% effective, which means there is a chance you could contract COVID-19. However, researchers believe you may be less likely to get as sick as you would if you were unvaccinated. If you have been vaccinated and test positive, you should self-isolate, monitor your symptoms and contact your physician.

Will the COVID-19 vaccine alter my DNA? What is an mRNA vaccine?

No, the COVID-19 vaccine will not alter your DNA. It also does not enter the nucleus of your cells. The COVID-19 vaccine is an mRNA vaccine. While this is the first mRNA vaccine, it uses a technology that scientists have been perfecting for decades. (Learn about other types of vaccines.)

In our bodies, our naturally created mRNA – or messenger RNA – deliver recipes to our cells on how to make specific proteins. An mRNA vaccine capitalizes on that process using laboratory-developed mRNA with information on how to defeat a virus. In this case, the COVID-19 vaccine delivers a blueprint to your cells on how to make the spike protein, an essential piece of the COVID-19 virus. This blueprint serves as a wanted ad, telling your body to be on the lookout for the spike protein and to develop an immune response to defeat it.

Then, your natural cell processes take over. After receiving both doses of the vaccine, your body will be prepared to identify and attack the SARS-CoV-2 virus, if it ever enters your system. And, within a matter of days, the mRNA from the vaccine is destroyed by our cells, leaving no permanent mark on our bodies.

Can I still get COVID-19 after being vaccinated?

Yes, it’s still possible for you to contract COVID-19, even after receiving the vaccine. No vaccine is 100% effective. However, your chances are much lower, and researchers believe you may be less likely to get as sick as you would if you were unvaccinated.

I’ve already had COVID-19. Should I still get the COVID-19 vaccine?

If you’ve had COVID-19 in the past 90 days, you can postpone getting your vaccine until that 90-day window has elapsed. If you are still symptomatic and infectious, you should postpone your vaccine until you are well and no longer contagious. Also, if you’ve been treated for COVID-19 with monoclonal antibodies or convalescent therapy in the past 90 days, you should postpone your vaccine until after the three-month window has passed. Otherwise, yes, you should still get the COVID-19 vaccine, even if you’ve had COVID-19.

Who should not get the COVID-19 vaccine?

At this time, you should not get the Pfizer/BioNTech COVID-19 vaccine if you have had a severe allergic reaction after a previous dose of this vaccine or if you’ve had a severe allergic reaction to any ingredient of this vaccine. You can see the ingredient list here. You can still get a vaccine if you have a food allergy. If you've ever had a severe allergic reaction, you will need to be monitored for 30 minutes after your vaccine. Consult your physician if you have any concerns about potential allergic reactions.

Patients with autoimmune disorders, such as Hashimoto’s thyroiditis, and those at a higher risk for contracting COVID-19 are encouraged to get the vaccine. In fact, many patients with heart and lung diseases were recruited for the COVID-19 clinical trials. Autoimmune disorders have been associated with vaccine adjuvants, which are agents added in vaccines to enhance immune responses, but there are no adjuvants in the mRNA vaccines.

Can children be vaccinated?

Yes, children can get vaccinated against COVID-19. The Pfizer vaccine has been approved for use in people ages 12 and up. 

How long will it take for the vaccine to start protecting me?

The vaccine immediately begins teaching your immune system what to look for to protect you against COVID-19. However, the amount of time it takes to gain full immunity to the virus will depend on what vaccine you receive. Generally, you should be protected about 14 days after you receive your second dose of the vaccine. Remember, skipping your second dose could leave you unprotected. The vaccine is not 100% effective, which means there is still a chance you could contract COVID-19. However, researchers believe you may be less likely to get as sick as you would if you were unvaccinated.

How many doses of the COVID-19 will be needed?

The Pfizer vaccine requires two doses, which are given three weeks apart (19–23 days after initial vaccination). The Moderna vaccine also requires two doses, which are given four weeks apart. Not taking the second injection could leave you unprotected.

How long will I be protected by the vaccine? Will I need to get vaccinated multiple times over my lifetime?

We don’t know how long immunity to COVID-19 will last. Some vaccines produce a lifetime of immunity but others — like the annual flu shot — require regular immunizations to provide continued protection. Clinical trials will continue even after the vaccines are authorized to keep studying the long-term safety and effectiveness of the vaccines. Currently, booster and third doses of the Pfizer vaccine are available to a limited group of people.

Will the current COVID-19 vaccines protect against the new virus strain?

Scientists believe the current vaccines will also protect against the mutated strain of COVID-19 that was first reported in England. However, similar to flu viruses, coronaviruses have a high rate of mutation, meaning they change slightly over time. It’s possible we may need an annual COVID-19 vaccine, in addition to our annual flu shot, to stay protected against mutations. However, because of the way mRNA vaccines are created, scientists can quickly isolate the part of the virus that needs to be recognized by our bodies and produce an effective vaccine.

How much does the COVID-19 vaccine cost?

The COVID-19 vaccine is free of charge to all Americans, regardless of insurance coverage, through 2021 as part of the federal government’s pandemic response. However, providers may be able to charge a small administrative fee for giving the shot, and this fee is reimbursable through insurance or the Health Resources and Services Administration’s Provider Relief Fund for the uninsured. Check with your provider to verify any fees.

Will I need to wear a mask and follow other restrictions after I get vaccinated? Can I still transmit COVID-19 to others after getting the vaccine?

You will still need to wear a mask after you’re vaccinated. It will take months for the majority of people to be vaccinated. We also do not know if the vaccine will reduce virus transmission. It is possible for people who have been vaccinated to still act as carriers for the virus and spread it to others, whether or not they show symptoms. People will need to wear masks, practice social distancing, wash their hands, and take other precautions for the foreseeable future, until we’ve reached herd immunity. Herd immunity occurs when a large portion of the population is vaccinated, making it difficult for infectious diseases to spread, because there are not many people who can be infected. Herd immunity works only if most people are vaccinated.

Stephen Weber, MD

Stephen Weber, MD

Stephen Weber, MD, has expertise in the management of a wide variety of infections. He serves as Chief Medical Officer and vice president for Clinical Effectiveness at UChicago Medicine.

Read more about Dr. Weber