COVID-19 Vaccine FAQs

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What is the COVID-19 vaccine?

The COVID-19 vaccine is a special type of drug designed to stimulate your immune system to recognize, attack and neutralize the SARS-CoV-2 virus, which is responsible for causing COVID-19.

Why are there different types of COVID-19 vaccines?

As part of the national effort to produce a vaccine capable of preventing COVID-19, vaccine developers tested many vaccine types to identify the most effective ones. Currently, three types of COVID-19 vaccines are in U.S. clinical trials. These include:

  • Protein subunit vaccines, which use a distinctive fragment—the spike, or S protein—of SARS-CoV-2 to trigger an immune response. Two vaccine developers using this technology include Novavax and Sanofi (in partnership with GlaxoSmithKline).
  • Viral vector vaccines, which are harmless viruses carrying the S protein gene. Viral vector vaccines mimic SARS-CoV-2 infection by producing the S protein, triggering the immune system to make antibodies against it. Two vaccine developers using this technology include Janssen Pharmaceuticals (a Johnson & Johnson company) and AstraZeneca-University of Oxford.
  • Nucleic acid vaccines, which give your body a message, or recipe to make the S protein. Your immune system reacts to the S protein and creates antibodies to it. Nucleic acid is DNA or RNA. The first two authorized vaccines—Pfizer-BioNTech and Moderna—are messenger RNA (mRNA) vaccines.

A fourth type of vaccine in production in other countries is an inactivated form of SARS-CoV-2. Flu and measles vaccines are examples of inactivated vaccines. There are no inactivated COVID-19 vaccines in U.S. clinical trials.

How effective are the COVID-19 vaccines?

The Pfizer-BioNTech and Moderna vaccines appear to be equally effective. In clinical trials, the Pfizer-BioNTech vaccine was 95% effective at preventing symptomatic COVID-19, across different races and age groups (16 and older). The Moderna vaccine was 94% effective at preventing symptomatic COVID-19, across different races. Moderna’s trial, in participants 18 and older, indicated the vaccine was less effective in people 65 and older, but this may be because there were fewer cases of COVID-19 in that age group compared to other age groups.

The third vaccine authorized for use is a viral vector vaccine from Janssen Pharmaceuticals, part of Johnson & Johnson. It is 66% effective, overall, at preventing moderate to severe COVID-19, based on clinical trials in several countries, including the United States. It is 85% effective at preventing severe COVID-19, and 100% effective in preventing COVID hospitalization and death. The Janssen vaccine trial was conducted during the emergence of new COVID-19 virus strains, including those discovered in South Africa and Latin America. The vaccine was 72% effective in the U.S., 66% effective in Latin America, and 57% effective in South Africa, at preventing moderate to severe COVID-19.

Who is eligible to receive the COVID-19 vaccine?

The Pfizer-BioNTech COVID-19 vaccine is authorized for people ages 16 and older. The Moderna and J&J vaccines are authorized for people ages 18 and older.

Most states are employing a phased approach to COVID-19 vaccination, with healthcare workers, essential public health and safety workers, the elderly, and other high-risk populations receiving the vaccine first. However, every state sets its own policies for who can be vaccinated—and when. Vaccine eligibility will change over time, as more people get vaccinated and more vaccine is available.

Can I be forced to get to the COVID-19 vaccine?

No. However, each state, municipality or corporation may be able to set rules regarding whether vaccines are mandated for certain categories of citizens and workers. As of January 2021, no court has heard challenges to mandatory COVID-19 vaccinations.

When will a vaccine be available for children?

Moderna and Pfizer-BioNTech are conducting additional trials in participants ages 12 to 15 (Pfizer) and ages 12 to 17 (Moderna). The AstraZeneca-Oxford vaccine, authorized in the U.K. and other countries, is also conducting a vaccine trial with teenagers. J&J is also conducting a trial with younger participants. Results should be available by the start of the 2021-22 school year this fall. Vaccine trials in children usually follow a step-down approach, so trials will study even younger children with time.

Why should I get vaccinated when I’m eligible?

COVID-19 is a public health and life-threatening emergency. Getting vaccinated will help you avoid getting sick and dying from COVID-19.

The COVID-19 vaccine works well to prevent development of the disease if you’re exposed to the SARS-CoV-2 virus, and to reduce the severity of symptoms if you do develop COVID-19, so they won’t become life threatening.

Now researchers are studying how well the vaccines keep you from being infected by the virus in the first place, and whether vaccination keeps an asymptomatic person from spreading the virus to others. Early results from the vaccine clinical trials and other data are promising and show that vaccination can also help prevent SARS-CoV-2 infection. If you do become infected after vaccination, being vaccinated will likely hamper the ability of the virus to multiply and spread to those around you, which will help end the pandemic.

If I already had COVID-19, should I still get a vaccine?

Yes. Natural SARS-CoV-2 antibodies (immunity) last for a few months; a recent U.K. study indicates natural immunity lasts at least six months, but the upper limit is still not known. This means it might be possible to become infected more than once.

Where do I get the COVID-19 vaccine?

Your state’s public health department can provide information about where to get a COVID-19 vaccine and when you might be eligible to receive one. In general, people have been receiving the vaccination at pharmacies, doctor’s offices, hospitals, specially designated mass vaccination sites at sports stadiums and similar venues, and many other locations. You may also select your state from the Centers for Disease Control and Prevention (CDC) vaccine center to see when and where you may be vaccinated, including specific pharmacy and supermarket chains.

How much does the COVID-19 vaccine cost?

The COVID-19 vaccine is free for all Americans. The U.S. Department of Health and Human Services is partnering with many major pharmacies and health networks to provide the vaccine with no out-of-pocket costs. Healthcare providers outside of a partnership may assess a fee for administering the injection.

How is COVID-19 vaccination performed?

A healthcare provider injects the vaccine into the upper arm muscle—the same place you receive a flu shot. Someone will monitor you for up to 30 minutes after receiving the injection to make sure you don’t experience a serious reaction. The vast majority of people tolerate the vaccine without serious symptoms.

What are the known COVID-19 vaccine side effects?

The vaccine should cause some side effects. These signs tell you your immune system is responding to the vaccine. Most people do not experience any serious or life-threatening reactions to the three approved COVID-19 vaccines. The most common side effects of the vaccines include:

  • Fatigue
  • Feeling ill, like you have the flu
  • Pain, redness or swelling at the injection site

How will I feel after I get the COVID-19 vaccine?

Most people experience mild discomfort at the injection site for a few days. Some people report feeling somewhat ill with flu-like symptoms within 24 hours of receiving either of the approved COVID-19 vaccines. Some people report that these symptoms occur more strongly after the second dose of the Pfizer-BioNTech vaccine. This is normal, and you should feel better within 48 hours. Acetaminophen (Tylenol) can help relieve pain, but take it after your vaccination appointment.

What are the potential risks and complications of the COVID-19 vaccine?

The Pfizer-BioNTech and Moderna COVID-19 vaccines have proven very safe for most people and did not cause any “serious, adverse events” in the thousands of clinical trial participants. However, since vaccination began in healthcare workers and other eligible groups in December 2020, there have been reports of allergic reactions—some severe—to both the Pfizer-BioNTech and Moderna vaccines. In an analysis of 1.8 million doses of the Pfizer-BioNTech vaccine administered, anaphylaxis occurred at a rate of 1 in 100,000 people. There have also been reports of allergic reactions to the Moderna COVID-19 vaccine.

Anaphylaxis following COVID-19 vaccine administration is rare, according to the CDC. Experts are currently assessing the risk of anaphylaxis with the COVID-19 vaccines compared to non-COVID-19 vaccines.

Anaphylaxis symptoms include:

  • Difficulty breathing
  • Loss of consciousness
  • Swelling of the lips, tongue, or throat

If these symptoms occur after receiving a vaccine, call 911 for emergency medical attention.

The Janssen COVID-19 vaccine uses a different technology and ingredients than the other two authorized vaccines. An information and fact sheet for recipients of the Janssen (J&J) vaccine states "there is a remote chance that the Janssen COVID-19 Vaccine could cause a severe allergic reaction." If a reaction occurred, it would likely occur within a few minutes to an hour after receiving the injection. The most common side effects are injection site pain, headache, fatigue, and muscle pain.

Once I receive the vaccine, how long does immunity to COVID-19 last?

No one yet knows how long the vaccine’s protection will last. It takes years of study to determine how long antibodies persist in the human body after receiving a vaccine. No one expects vaccination to deliver lifelong immunity to COVID-19, but it may protect you for a year or two. It’s likely people will need a booster vaccination to keep immunity strong. It’s also possible a new vaccine is necessary to protect against future variants of SARS-CoV-2, similar to an annual flu shot.

Clinical trial conductors are following the participants of the COVID-19 vaccine clinical trials for two years to analyze the long-term safety of the vaccines and determine how long immunity lasts. Available research data forecasts that immunity gained with the current vaccines will last at least a year if not longer.

How many people have to get vaccinated to reach herd immunity?

Herd immunity is when enough people are immune that more vulnerable groups are indirectly protected from the disease. A vaccine is a faster and much safer way to reach herd immunity than exposing people to a life-threatening infection. Experts estimate 75 to 90% of the population needs to be vaccinated before achieving herd immunity. For the United States, with a population of about 330 million, more than 200 million people would need to be vaccinated to reach herd immunity.

How long will it take for the general public to be vaccinated?

Estimates vary on how long vaccination will take. Each state currently sets its own guidelines regarding who can be vaccinated and when. An early estimate is summer 2021.

Can I stop wearing a face mask and see my friends again after we’re all vaccinated?

No. It takes several days after the injection for the body to begin manufacturing protective antibodies against SARS-CoV-2. With the Pfizer and Moderna vaccines, achieving full immunity requires two doses of the vaccine, spaced weeks apart. You can be vaccinated but still become infected while your body builds immunity. It will be safe to congregate again and stop wearing masks in public when we are closer to herd immunity.

What happens if I miss the second dose of COVID-19 vaccine?

If you received a COVID-19 vaccine that requires two doses, and you miss the second dose, you should get it as soon as possible. The first dose of vaccine primes the immune system, but the second shot gives it a boost and is necessary to reach 94 to 95% effectiveness (with the mRNA vaccines) at preventing mild to severe COVID-19. Janssen's vaccine is a single-dose regimen.

There is some evidence from the clinical trials that the Pfizer vaccine is 82% effective after one dose and the Moderna vaccine 80% effective. More studies are necessary to support those percentages and to understand how long that level of immunity will last. However, the CDC issued a variation to the mRNA vaccine dosing schedule "if it is not feasible to adhere to the recommended interval": The second dose can be administered up to 4 days earlier and 6 weeks after the first dose. If the second dose is administered beyond these intervals, there is no need to restart the vaccination series.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 21
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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