COVID-19 Vaccine Frequently Asked Questions

How do vaccines work?

Vaccines trigger the body’s natural response to fight illnesses.  Vaccines work by training the immune system to be ready to recognize viruses or bacteria when they enter the body. Then, if a person is exposed to that virus or bacteria, their immune system knows how to respond. The COVID-19 vaccines protect people from getting seriously ill and requiring hospitalization. If a vaccinated person gets COVID-19, they usually have mild symptoms.

Is the COVID-19 vaccine safe?

Yes. The Federal Drug and Administration (FDA) works to make sure that all vaccines are as safe as possible through careful testing. So far, the FDA has provided emergency use authorization for the Moderna and Johnson & Johnson COVID-19 vaccines and full approval for the Pfizer-BioNTech vaccine. Although the vaccines are new, the process for ensuring vaccine safety is not new. All vaccines must meet strict safety standards before being released to the public. Many thousands of adults of different ages and races volunteered for clinical trials to test the COVID-19 vaccines, and more than 170 million Americans are fully vaccinated. The FDA and others continue to track side effects and watch for any safety concerns.

How many shots are needed?

The Moderna and Pfizer-BioNtech vaccines require two doses, spaced several weeks apart, to be fully effective. The Johnson & Johnson vaccine works with just one dose instead of two. 

Is the COVID-19 vaccine effective against the Delta variant?

Yes. Even though the Delta variant spreads more easily and breakthrough cases can occur, the vaccines protect people from becoming very sick, being hospitalized, or dying from COVID-19. Delta is one example of a variant. The virus may change again over time creating new variants, and scientists will continue to monitor and study these variants. Vaccinating people is one of the best strategies to decrease the development of new variants.

What’s in the COVID-19 vaccine?

The Moderna and Pfizer-BioNTech vaccines have messenger RNA (mRNA), genetic material that our cells use to make spike proteins. Then our bodies respond by making antibodies. These COVID-19 vaccines do not have preservatives, which is why they must stay frozen until they are ready to use. The Johnson & Johnson vaccine does not use mRNA. Instead, it has a modified adenovirus that delivers instructions for the body to make antibodies to the coronavirus's spike protein. The vaccines also have lipids, salts, sugars, acids, and acid stabilizers to help keep them stable to deliver the active ingredient to our cells. The vaccines do not contain ingredients that are poisonous or harmful. There is no coronavirus in the vaccines, which means the vaccines cannot cause COVID-19.

Will mRNA change my DNA?

No. When the mRNA enters a cell it provides instructions to make a spike protein similar to that of the SARS-CoV-2 virus (the virus that causes COVID-19). Your body responds by making antibodies to recognize the spike protein. After you have the spike protein in your body, the mRNA is destroyed. It will not mix with your DNA.

Are there side effects?

Yes. The most common side effect is pain in the arm where you get the shot. Some people also have one or more of these symptoms: tiredness, headache, muscle pain, chills, joint pain, and fever. Another side effect is swollen lymph nodes in the neck or under the arm where the shot was given. These are all signs of the body’s immune system working! More people had these side effects after the second dose than after the first dose.

A very small number of the many people vaccinated have had more serious side effects such as a severe allergic reaction.  Talk to your health care provider if you have had a severe allergic reaction to other vaccines or any ingredients in the COVID-19 vaccines. Your health care provider can help you decide if it is safe for you to receive the COVID-19 vaccine.

Should people who have already had COVID-19 get the vaccine?

Yes. People who have had COVID-19 may have some immunity against the coronavirus, but this immunity can be weak and may not last long. Most people develop more antibodies to the coronavirus after they are fully vaccinated than after getting COVID-19. The vaccine will help your body have a stronger response if you get COVID-19 again. People with COVID-19 should wait until they are no longer infected, and check with their health care provider before getting the vaccine.

Am I protected as soon as I receive the vaccine?

No.  It takes time to build immunity in response to the vaccines. The Centers for Disease Control (CDC) considers people “fully vaccinated” against COVID-19 when at least 2 weeks have passed since their final dose. For the Pfizer and Moderna vaccines this is two weeks after the second dose, and for the Johnson & Johnson vaccine this is two weeks following the single dose.

Do I still need to wear a mask after I’ve had the vaccine?

Yes. The vaccine is an important way to stay safe, but for now, continue to follow all public health orders including wearing masks, maintaining physical distance, avoiding crowds, and washing your hands. The vaccine is not 100 percent effective, and we need to protect the young children we spend time with since they will not be fully vaccinated for a while. We are still learning about COVID-19 and its variants, and we don’t know when community spread of the virus will stabilize. Getting vaccinated is a very important step to protect against COVID-19 variants and severe illness, but wearing masks is one of the risk reduction strategies that we must continue.

Who can get the vaccine?

Anyone 12 years and older can get the vaccine. Californians can go to to sign up for an appointment and receive updates about new appointments and locations.

Where will I get the vaccine?

This will vary by county. It's best to check with your local public health department or primary care provider about where the vaccine will be available in your location.

What does the vaccine cost?

Most health care plans and county health departments provide the vaccine free of charge.

Is the vaccine required for child care workers?

Getting the COVID-19 vaccine is voluntary. But more and more employers, including California’s public and private K-12 schools and Head Start, are requiring vaccination for their workers. Some people are not eligible to get the vaccine because of their health status and may opt for regular COVID-19 testing instead.

Are young children eligible to get the COVID-19 vaccine?

No. At this point, the COVID-19 vaccine has not been approved for children younger than 12 years old, although the approval process is underway. Current vaccine laws for child care enrollment do not include the COVID-19 vaccine.

How long will immunity last after the vaccine?

It is not unusual for immunity to decrease over time after vaccination. A third dose of Pfizer or Moderna COVID-19 vaccines are now available for adults with moderately to severely compromised immune systems.  Boosters have been recommended for adults 65 years and older and adults who are at higher risk of severe disease. Adults who may be exposed to COVID-19 at work, including teachers and child care staff, may also choose to get a booster. U.S health officials will continue to monitor how long the vaccine protects against COVID-19.

Is the vaccine recommended for pregnant people?

Yes. The COVID-19 vaccination is recommended for pregnant people. The CDC recommends that all people who are pregnant, breastfeeding, trying to get pregnant, or might become pregnant in the future be vaccinated for COVID-19. Pregnant people are more likely to get severely ill if they get COVID-19 compared with non-pregnant people. People who contract COVID-19 while pregnant also face a higher risk of having a preterm birth. Getting a COVID-19 vaccine during pregnancy can protect you and your baby. Pregnant people should talk to their health care providers about getting the vaccine.

Once I’m vaccinated, do I need to quarantine if I’m exposed to someone with suspected or confirmed COVID-19?

No. Fully vaccinated people who have close contact with someone with suspected or confirmed COVID-19 should be tested 3-5 days after exposure, and wear a mask in public indoor settings for 14 days or until they receive a negative test. Isolate for 10 days if your test result is positive.

This collection of questions and answers was made possible with funding from the Heising-Simons Foundation.

updated 10/5/2021