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Photo ofdoctor in gloves holding syringe and making injection to senior patient in medical mask. Covid-19 or coronavirus vaccine

We will update this post as news comes out about COVID-19 vaccines. This post was last updated on May 18, 2022. Many questions and answers below come from our “COVID-19 Vaccine: Allergy, Anaphylaxis and Answers” webinar.

Are vaccines effective?

Absolutely! Vaccines save lives. They are one of the greatest public health achievements of the 20th century.

What are the benefits to the COVID-19 vaccine?

COVID-19 can be a very serious illness. The vaccines have been shown to be highly effective in preventing the virus. They allow your body to develop immunity to the virus without getting sick. If someone who is vaccinated does get diagnosed with COVID-19, they are much less likely to experience severe illness. It is also believed that getting vaccinated protects people around you as well. Getting sick with COVID-19 provides a level of immunity, but how long is unknown. And the illness brings risk of severe symptoms or death. Thus, developing immunity through vaccination is the safest choice.

Photo of COVID SDM Graphic

How many COVID-19 vaccines are available?

There are three COVID-19 vaccines available in the United States:

  1. Pfizer/BioNTech (two doses three weeks apart)
  2. Moderna (two doses four weeks apart)
  3. Johnson & Johnson (one dose)

The Pfizer/BioNTech vaccine for teenagers 16 and older and adults has received full approval from FDA. It is marketed under the brand name Comirnaty. The Moderna vaccine for adults 18 years of age and older has also received full approval from FDA. It is marketed under the brand name Spikevax. Johnson & Johnson is available for adults 18 years of age and older under an Emergency Use Authorization from the U.S. Food and Drug Administration (FDA). However, FDA has restricted its use to people who are unable to get either of the other two vaccines. FDA says the Johnson & Johnson vaccine is linked to a rare but potentially life-threatening blood clot condition called thrombosis with thrombocytopenia syndrome. The Pfizer/BioNTech vaccine for children ages 5-11 and 12-15 is approved under an Emergency Use Authorization. The dosage of the Pfizer/BioNTech vaccine for the 5-11 age group is 10 mcg, or one-third of what is given to people ages 12 and older (30 mcg).

What types of COVID-19 vaccines are there?

Messenger RNA (mRNA) vaccines

The mRNA vaccines do not contain the live virus, but rather a synthetic material that mimics the virus. This sends your body a message to produce antibodies and t-cells that build up an immune system defense. It protects people from getting infected when exposed to the real virus. The Pfizer/BioNTech and Moderna vaccines are mRNA vaccines.

Viral vector vaccines

Viral vector vaccines use a common cold virus as a vector with genetic code from COVID-19 introduced into it. The vaccine delivers the genetic code to our cells and trains our immune system to protect itself from future infections. The vaccine does not contain a live virus. It cannot cause an infection from either COVID-19 or the vector virus. The Johnson & Johnson vaccine is a viral vector vaccine.

How effective are the COVID-19 vaccines?

The Pfizer/BioNTech vaccine is reported to be 95% effective in preventing symptomatic COVID-19 illness in older teens and adults. A clinical trial involving children ages 12-15 showed the vaccine was 100% effective in children ages 12-15. Nearly 2,300 adolescents participated in the clinical trial. Half were given the vaccine and half were given a placebo. None of the children who received the vaccine got COVID-19, while 16 in the placebo group did get it. In addition, researchers said the vaccine’s antibody buildup was stronger in the 12-15 age group than for older teens and adults. A clinical trial of the 5-11 age group, conducted by Pfizer/BioNTech and presented to FDA, showed the vaccine was 90.7% effective against symptomatic COVID-19. The antibody response to the vaccine was comparable to what is seen in people 16-25 years old. The Moderna vaccine is reported to be 94.5% effective in preventing symptomatic COVID-19 illness. This vaccine is only available for people ages 16 and older at this time. The Johnson & Johnson vaccine is reported to be 85% effective in preventing severe or critical COVID-19 illness and 66% effective in preventing moderate COVID-19 illness.

Who gets the vaccine and when?

Everyone 5 years of age and older is eligible to get a COVID-19 vaccination, according to CDC. Check the websites of your state and local departments of health for information about vaccine availability in your area, or visit

What is the COVID-19 vaccine booster shot?

Research shows COVID-19 vaccines decline in effectiveness against severe illness, hospitalization and death over time. The COVID-19 booster shot can bolster protection against COVID-19, including against variants. The booster shot may be particularly beneficial for people with moderate to severe asthma, COPD and other respiratory diseases. Studies show that people who are immunocompromised may not develop enough COVID-19 vaccine-induced antibodies to fend off severe illness. COVID-19 booster shots have been approved for children ages 5-17 and adults 18 years of age or older. Booster shots are available for Pfizer/BioNTech, Moderna and Johnson & Johnson vaccines. Children are only eligible to get the Pfizer/BioNTech vaccine and booster at this time. It is recommended people receive the same vaccine dose as their initial series. However, people may receive a booster shot of a different vaccine than the one they received as their original dose, according to FDA. The booster dose for Pfizer/BioNTech and Moderna vaccines would be administered six months after a person received the second dose of the vaccine. The booster dose for Johnson & Johnson would be given two months after a person received their dose. Side effects to the vaccine booster shot are similar to side effects of the initial vaccine dose. The booster dose, just like the initial dose series, is safe for pregnant women and has not been linked to any fertility concerns.

Will people who are immunocompromised need a third dose of the COVID-19 vaccine?

CDC says people who are moderately or severely immunocompromised should receive a third dose of the mRNA COVID-19 vaccine. (This is not a booster shot, CDC notes.) People who are moderately or severely immunocompromised are especially vulnerable to COVID-19 because they are more at risk for serious, prolonged illness. They may not be able to build the same level of immunity to two doses compared to people who are not immunocompromised. This third dose is approved for adults and children between the ages of 5 and 17 who are immunocompromised. People who are immunocompromised include those who…

  • are receiving cancer treatment
  • have moderate or severe primary immunodeficiency disease
  • take high doses of corticosteroids (20mg or more of prednisone or equivalent per day) or other drugs that may suppress the immune system
  • received an organ or stem cell transplant

If you have a medical condition that makes you immunocompromised, or you are prescribed high doses or long-term doses of corticosteroids, talk with your doctor about whether getting an additional dose of COVID-19 vaccine if necessary. CDC recommends people who are moderately or severely immunocompromised get their third dose at least four weeks after the second dose of a mRNA vaccine. Research is ongoing whether another dose of the Johnson & Johnson vector vaccine is necessary for immunocompromised people.

What should I know about the Pfizer/BioNTech vaccine?

  • First vaccine to be fully approved for ages 5 and older by FDA
  • Vaccine will be marketed under the brand name Comirnaty
  • Vaccine is approved for 5-11 and 12-15 age groups as an Emergency Use Authorization
  • mRNA vaccine
  • Only vaccine currently available for 5-11 and 12-15 age groups
  • 2 doses, 3 weeks apart
  • Only vaccine in which a booster shot is available (for people 65 years of age or older and adults at risk of severe illness)
  • Ingredients
  • Potential for side effects:
    • Pain at injection site
    • Flu-like symptoms
  • Must be stored very cold (-70 degrees F), making it less accessible for smaller facilities

What should I know about the Moderna vaccine?

  • Fully approved by FDA for ages 18 and older
  • Vaccine will be marketed under the brand name Spikevax.
  • mRNA vaccine
  • 2 doses, 4 weeks apart
  • Ingredients
  • Slightly more effective in younger people than older people
  • Potential for side effects
    • Pain at injection site
    • Flu-like symptoms
  • Can be stored at 36 degrees F to 46 degrees F, making it more accessible

What should I know about the Johnson & Johnson vaccine?

  • Vector vaccine
  • Approved as a single dose
  • Approved as an emergency use authorization by FDA
  • As of May 2022, FDA has restricted its use to people who are unable to receive either the Pfizer/BioNTech or Moderna vaccines. This is due to a rare but life-threatening blood clotting syndrome linked to the vaccine.
  • Ingredients
  • May be more effective against COVID-19 variants that have surfaced around the world
  • Potential for side effects
    • Pain at injection site
    • Flu-like symptoms
  • Can be stored in refrigerated temperatures and not in a freezer, making it more accessible and easier to transport

Are there other COVID-19 vaccines likely to be available soon?


  • Vector vaccine
  • 90% effective when half dose is given.
  • 2 doses, 1 month apart
  • Does not require special cooling.

What are the side effects of the COVID-19 vaccines?

The COVID-19 vaccine may cause:

  • Pain and/or swelling at the injection site.
  • Fever
  • Chills
  • Fatigue
  • Headache

These symptoms are normal as the body works to build immunity to the virus.

How can COVID-19 vaccine side effects be managed?

Not everyone will develop side effects from the COVID-19 vaccine. If you do have side effects, there are things you can do to minimize the symptoms including:

  • Using a cool, wet and clean towel over the injection site
  • Moving the affected arm
  • For fever – drink lots of fluids and wear light clothing
  • Even if you have side effects from the Pfizer/BioNTech and Moderna vaccines, it is important you get the second dose unless your doctor advises against it due to the risk of an allergic reaction to the vaccine ingredients.

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Should you take pain relief medications such as Tylenol or Motrin before getting the COVID-19 vaccination?

The U.S. Centers for Disease Control and Prevention (CDC) does not recommend taking pain relief medication before vaccination. It is unknown if those medications will decrease the effectiveness of the vaccine. For pain, discomfort or fever after the vaccine, you may take these medicines as long as you have no medical reason to avoid them.

Do I need to get vaccinated if I already had COVID-19?

People who already had COVID-19 should get the vaccine. Vaccination provides more robust and durable protection against COVID-19 that immunity from natural infection. Natural infection does provide some immunity, but it is unknown how long the immunity lasts.

How long should people wait to get the COVID-19 vaccine after having COVID-19?

There is no specific timeframe for vaccination after COVID-19. However, people should wait until they no longer have any symptoms. If someone is treated with monoclonal antibodies, then they should wait 90 days before getting the vaccine. People may also need to wait if they received a vaccine for another disease recently.

Is the COVID-19 vaccine effective against new variants or strains of the virus?

It is common for viruses to mutate over time leading to new variants. There are multiple COVID-19 variants that have emerged over the past several months, including the so-called Delta variant that has caused a rise in infections, hospitalizations and deaths in the United States. Thus far, the COVID-19 vaccines are effective in producing antibodies to the new variants. However, the vaccines and variants will require ongoing study.

Can you get sick with COVID-19 even after you have been vaccinated?

Yes, people can still catch the virus after getting vaccinated. CDC is calling these “vaccine breakthrough cases.” However, most people who do get COVID-19 post-vaccination develop mild symptoms and are less likely to get hospitalized or die from the virus. Remember, no vaccine is 100% effective. In clinical trials, the Pfizer/BioNTech vaccine was shown to be 95% effective in preventing symptomatic illness. The Moderna vaccine was shown to be 94.5% effective in preventing symptomatic illness. The Johnson & Johnson vaccine was 66% effective in preventing moderate to severe COVID-19, and 85% effective in preventing severe or critical disease.

What guidelines should be followed after you receive the COVID-19 vaccine?

First off, if you’re getting the Pfizer/BioNTech or Moderna vaccines, it is important that you get both doses of these vaccines. You are not fully protected until about two weeks after your second shot. When you are fully vaccinated with a COVID-19 vaccine, it’s important to continue to practice infection prevention measures. This is partly because the vaccines are not 100% effective. Also, it is unknown if people who are vaccinated can still carry and transmit the virus. So, until enough people are immune it is important that everyone follow guidelines including:

  • Social distancing — 6 feet separation from others
  • Frequent handwashing
  • Wear a mask

If you are fully vaccinated and exposed to someone with COVID-19, should you still self-quarantine?

People who are fully vaccinated and are exposed to COVID-19 do not need to self-quarantine if they meet conditions established by the CDC:

  • Fully vaccinated – 2 weeks or more since second dose of two-dose vaccine or since first dose of single-dose vaccine
  • Within 3 months of receiving last dose of COVID-19 vaccine
  • No symptoms of COVID-19 since exposure

Is it okay for people with a history of allergies to get the COVID-19 vaccine?

People with a history of allergies or allergic reactions can receive the vaccine. People who are allergic to any of the vaccine’s ingredients or had an allergic reaction to a first dose should not receive the vaccine. They should receive the vaccine at a medical facility where they can be monitored for 30 minutes post-vaccination. Learn more on our COVID-19 Vaccine Allergic Reactions page.

Is it okay for pregnant women to get vaccinated against COVID-19?

Yes. CDC recommends COVID-19 vaccination for women who are pregnant, recently pregnant (including those who are lactating), who are trying to become pregnant, and/or who might become pregnant in the future. It’s beneficial to both mother and baby. A recent study published in the American Journal of Obstetrics and Gynecology found that infants born to mothers who received the Pfizer/BioNTech vaccine or Moderna vaccine had high levels of protective antibodies. The study shows that antibodies the mother builds from the vaccine cross the placenta and go to the baby. This has the potential of protecting the baby in the first days of life from getting a COVID-19 infection. The study also found antibodies can be shared between a mother and a baby through breast milk in lactating women who received the Pfizer/BioNTech vaccine.

Will antihistamines reduce the antibody response to a vaccine?

There is no data indicating that antihistamines reduce antibody responses. Oral steroids, however, may reduce antibody response.

Are there any medical conditions that may exclude someone from getting the COVID-19 vaccine?

Not currently. People with underlying medical conditions such as asthma or COPD, weakened immune systems, autoimmune conditions, Guillain-Barre syndrome and Bell’s Palsy should get the mRNA vaccine.

Does taking Tylenol after the vaccine make it less likely to produce an immune response?

No. The only medication that could potentially interfere with the vaccine is oral corticosteroids, which may reduce the antibody response.

Reviewed by: Bradley Chipps, MD, FACAAI, is a board-certified allergist and pediatric pulmonologist with Capital Allergy and Respiratory Disease Center in Sacramento, California. He earned his medical degree from University of Texas Medical Branch in Galveston in 1972. He is Past President of the American College of Allergy, Asthma and Immunology (ACAAI).