Frequently Asked Questions About COVID-19 Vaccines

Only one year after the novel coronavirus (SARS-CoV-2) first emerged, the US has begun a national COVID-19 vaccination program. The following information addresses frequently asked questions by both the public as well as healthcare professionals.

Note: Information about COVID-19 is changing rapidly. View the latest information from the Centers for Disease Control and Prevention (CDC) and information specific to COVID-19 vaccination.

About the Vaccines

What is an mRNA vaccine? Do mRNA vaccines affect DNA?

Messenger RNA (mRNA) is found in all living cells. mRNA vaccines work by teaching cells how to make a protein or a piece of a protein that triggers an immune response inside the body. That immune response, which produces antibodies, is what protects against infection if an individual is exposed to the virus.

mRNA is not the same as DNA, and it cannot combine with our DNA to change our genetic code. It is also relatively fragile, and will only hang around inside a cell for about 72 hours, before being degraded. mRNA vaccines do not affect or interact with DNA in any way. mRNA never enters the nucleus of the cell, which is where DNA (genetic material) is stored.

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What is the timeframe between the two doses? Do you have to get both doses from the same company?

With both vaccines, two doses are recommended, and both doses must come from the same manufacturer. When you are vaccinated, you should receive a card as a record indicating which vaccine you received.

The second dose of the Pfizer-BioNTech vaccine is given at 21 days. The second dose of the Moderna vaccine is given at 28 days. Do not get the second dose sooner than recommended, but if the second dose is delayed, get the second dose as soon as possible.

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When will vaccines be available for the general public?

Initially, COVID-19 vaccines will be given to healthcare professionals and long-term care residents (individuals who work or live in nursing homes). As supply increases, vaccines may be given to adults age 75 and older and frontline essential workers who are at risk for exposure. Next, vaccines may be offered to adults who have high-risk medical conditions and other individuals who are at high risk of being exposed to COVID-19 or having severe health outcomes.

This process will take months. It is important to continue wearing masks, social distancing, avoiding crowds, washing hands, and taking recommended steps to help stop the spread of the virus.

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When will vaccines be available for children?

Because children were not included in the first set of clinical trials, the vaccines are not currently recommended for children under the age of 16 years. Clinical trials in younger children are underway, and presuming the trials are successful, vaccine recommendations for children will be made once the trials are completed.

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For how long are the vaccines effective? Will individuals need to be revaccinated each year?

Scientists do not yet know how long the protection from the COVID-19 vaccines will last. These are new vaccines for a disease that emerged only recently, which means there are not yet long-term data. Vaccine researchers and public health experts are closely monitoring vaccine effectiveness and safety, and new information will be shared by the Centers for Disease Control and Prevention (CDC) as it becomes available.

Some vaccines provide life-long protection, such as the measles vaccine. Others require booster doses. For influenza (flu), everyone age 6 months and older should get vaccinated each year.

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Vaccine Safety

How do we know that the vaccines are safe?

All vaccines used in the US are required to go through extensive safety testing before they are licensed by the US Food and Drug Administration (FDA) or recommended for widespread use.

The new COVID-19 vaccines have been studied in multiple clinical trials, each of which has included thousands of individuals who were followed for a minimum of two months. Decades of experience with other vaccines indicate that the vast majority of adverse reactions occur within the first two months of vaccination.

Vaccinated individuals may have a sore arm, fatigue, headache, and even low-grade fever that lasts one or two days. This is to be expected, and it indicates that the vaccine is working.

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Are COVID-19 vaccines safe for people with allergies?

Individuals who have had severe allergic reactions to other vaccines or injectable therapies should not get vaccinated against COVID-19. People who have other allergies (e.g., allergies to food, animals, venom, environmental, or latex) may be vaccinated but should remain at the vaccination site for 15-30 minutes for observation. Individuals who carry epinephrine (EpiPen©) should bring it with them as a precaution.

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Is it safe to get a COVID-19 vaccine while pregnant or breastfeeding? Do COVID-19 vaccines affect fertility?

Pregnant individuals who are eligible to receive a COVID-19 vaccine may choose to be vaccinated. Breastfeeding is rarely a safety concern with vaccines. There is no evidence that COVID-19 vaccines can reduce fertility. Talk with a healthcare professional if you have questions about getting vaccinated.

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How long after receiving a COVID-19 vaccine are you able to take an antibiotic safely?

There is no influence or interaction between antibiotics and COVID-19 vaccines, so when indicated, antibiotics may be taken at any time relative to COVID-19 vaccine administration.

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Is it possible to get COVID-19 after receiving the vaccine? What side effects should people expect from the vaccines?

None of the new vaccines contain the live virus that causes COVID-19, so it is not possible to get the disease from the vaccine. Some individuals who are vaccinated may have a sore arm, fever, or other symptoms. These symptoms are normal and are a sign that the body is building immunity.

It typically takes a few weeks for the body to build immunity after vaccination. That means it is possible for an individual to be infected with the virus that causes COVID-19 just before or just after vaccination, as the vaccine has not had enough time to provide protection.

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Getting Vaccinated

Does someone who has already had COVID-19 need to get vaccinated?

CDC recommends that COVID-19 vaccine be given to individuals regardless of whether or not they were previously infected.

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Will individuals be required to show proof of vaccination to return to work or school?

Vaccine mandates cannot be imposed federally, but some employers may require proof of vaccination.

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Will COVID-19 vaccines work against new mutations of COVID-19?

Viruses constantly mutate, and public health experts expect new variants of a virus to occur. Multiple variants of SARS-CoV-2 (the virus that causes COVID-19) have been documented in the US and globally, including B117, which first emerged in the United Kingdom, and 501Y.V2, which emerged in South Africa.

Scientists are monitoring changes in the virus, and information about these variants is rapidly emerging. The new variants seem to spread more easily and quickly, but at this time, there is no evidence that the variants cause more severe illness or increased risk of death, or make COVID-19 vaccines less effective. Existing vaccines are expected to be effective against the variants and others that may emerge in the short term.

View current CDC information about emerging SARS-CoV-2 variants

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Can I get a COVID-19 vaccine at the same time as another vaccine?

The Centers for Disease Control and Prevention recommends waiting at least 14 days between getting a COVID-19 vaccine and getting any other vaccine, including a shingles vaccine or influenza (flu) vaccine.

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When can we expect to return to normal?

Recommended public health measures (including social distancing, face masks, and handwashing) will still be necessary to help slow or stop the spread of COVID-19:

  • While the vaccines appear to be highly effective at preventing disease, they may not prevent asymptomatic infection, meaning that those who have been vaccinated might still be able to get infected without experiencing any symptoms, and, therefore, unknowingly spread the virus.
  • Scientists estimate that to control COVID-19, about 70-80 percent will need to be immune (~250 million individuals in the US). Between March and November 2020, more than 250,000 people died and almost 12 million people in the US were infected, although estimates from antibody studies suggest that the number of those infected might be 3-7 times greater. Despite this, the virus continues to spread, demonstrating just how many more people need to become immune before we can expect to control the spread of COVID-19. To rely on infections alone to stop the spread of COVID-19, between 1 million and 5.4 million people would die before 250 million become immune.


Updated February 2021

Sources: Centers for Disease Control and Prevention, Food and Drug Administration

Learn more about coronaviruses at

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