Updated August 23, 2021
How do COVID-19 vaccines work?
Two COVID-19 vaccines use messenger RNA (mRNA), which is a set of instructions that tells a cell to make a specific protein. For SARS-CoV-2 (COVID-19), this is the spike protein that is found on the surface of the viral envelope. The mRNA used in the vaccines don’t enter the cell’s nucleus and has no interaction with a cell’s DNA. It is also not a full virus and cannot replicate itself. The mRNA is rapidly broken down by the cell once the instructions have been transmitted, so it doesn’t cause mutations or cellular defects, and has not been associated with infertility.
The other vaccine uses a modified adenovirus that contains DNA for the spike protein. The adenovirus is able to enter a cell and cause the spike protein to be made. Adenoviruses are a source of the common cold, but this particular virus can’t replicate so it won’t cause disease.
Once the spike protein is made, it is put on the surface of the cell, where it is seen by the immune cells and causes them to become activated and respond. The result is the production of neutralizing antibodies. If a person who is immunized becomes infected with the virus, the neutralizing antibodies will bind to the virus and prevent it from entering cells and causing disease.
Can the vaccines cause COVID-19?
No. An mRNA vaccine is not a virus and can’t cause disease. Because it activates the immune system, it can cause mild symptoms in some people (e.g., fatigue, achiness, fever). Based on data from the clinical trials, the most common reactions to the vaccine are pain at the injection site, fatigue, headache, and muscle aches. These symptoms are very common with other vaccines, including the flu shot, and are a sign that the body is responding to the vaccine.
The other authorized vaccine uses a modified virus that can’t replicate and does not cause any disease, including COVID-19.
What vaccines are available?
There are currently three vaccines in the U.S. against COVID-19. The Pfizer-BioNTech mRNA vaccine, Comirnaty, was given full approval by the FDA for individuals 16 years and older. It is still is under emergency use authorization for individuals aged 12-15. The Moderna mRNA vaccine and Janssen (Johnson & Johnson) adenovirus vaccine were authorized for individuals 18 years and older. All three vaccines were recommended by the CDC’s Advisory Committee on Immunization Practices (ACIP).
Additionally, the mRNA vaccines have been authorized for an additional dose following the primary series for individuals who are moderately to severely immunosuppressed. Booster doses for other individuals have not been authorized or recommended at this time. Vaccines are available in doctor offices, pharmacies, and community locations. Find out where to get the vaccine at vaccines.gov.
What is the difference between the emergency use authorization and licensure (approval) by the FDA?
Emergency use authorization (EUA) is a process by which the FDA can authorize use of a medication or vaccine with less data if the benefit of the vaccine has been shown to outweigh the risk. EUAs can be issued only during a declared emergency, such as the COVID-19 pandemic. Vaccines issued an EUA will continue to be studied to ensure they meet the high standards for safety, effectiveness, and manufacturing quality the FDA requires of an approved product.
The FDA has approved the first COVID-19 vaccine, Pfizer/BioNTech, for individuals 16 years of age and older.
What are the differences between the COVID-19 vaccines?
Two of the vaccines are mRNA vaccines that have a piece of mRNA specific for the SARS-CoV-2 spike protein. They have similar efficacy and safety profiles. The third vaccine uses a non-replicating adenovirus to deliver the spike protein into nearby cells. None of the vaccines use live viruses so there is no risk of infection. The main differences between the vaccines include the ages of individuals eligible to get the vaccines, the length of time between doses, the number of doses, the cold chain requirements for storage, and the preparation of the vaccine.
Approved for 16 and older
EUA for ages 12-15;
|EUA for ages 18 and older;
an additional dose for
|EUA for ages 18 and older|
|Ages eligible for vaccine||12 and older||18 and older||18 and older|
|Length of time between doses||21 days||28 days||n/a single dose|
|Storage requirements||-80 C; stable at -20 C for 2 weeks and at 4 C
for 30 days once mixed
|-20 C; stable at 4 C for 30 days||-20 C; stable at 4 C for 90 days|
|Preparation of vaccine||Reconstitution of lyophilized powder—
5 doses per vial
|No dilution needed—
10 doses per vial
|No dilution needed—
5 doses per vial
Why should I get a vaccine?
All COVID-19 vaccines are effective at preventing COVID-19, hospitalizations and death. By getting vaccinated, you are reducing your risk of disease, hospitalization, severe complications, and even death. Reducing the risk of disease also prevents the health care system from being overwhelmed.
While it is still possible to pass the virus to others if you are vaccinated, the risk is significantly lower. However, to prevent the spread of the highly contagious Delta, vaccinated individuals should wear masks in indoor public areas (schools, businesses, etc).
What does it cost to get the vaccine?
COVID-19 vaccines available at no cost to individuals, and clinicians administering the vaccine will be reimbursed for vaccine administration. See guidance on coding and payment.
Should I take any pain medications before getting the vaccine?
No. It is not recommended for people to take pain relievers before getting the vaccine as it is not known how these medications may affect how well the vaccine works. Get tips on relieving pain and discomfort AFTER the vaccine.
How many doses are needed?
The mRNA vaccines require two doses; the Pfizer-BioNTech vaccine should be given 21 days apart and the Moderna vaccine doses should be spaced 28 days apart for an effective immune response. Recipients should get the second dose from the same manufacturer as their first dose. However, if they get a dose of a different vaccine, no additional doses are needed, and the series is considered complete. The Johnson & Johnson vaccine is a single dose.
Individuals with moderate to severe immunosuppression may receive an additional dose 28 days after to conclusion of their the primary series of either of the mRNA COVID-19 vaccines. At this time individuals who received the Johnson & Johnson vaccine are not currently eligible to receive an additional dose. The FDA and CDC are working to obtain data to support additional doses in this group.
What are the side effects of the vaccine?
Data from the clinical trials of all three candidates indicate that the most common reactions were pain at the injection site, fatigue, headache, and muscle aches. These symptoms are commonly seen with other vaccines. A few people also reported fever and nausea. These symptoms were observed in adolescents as well as adults.
No serious side effects were seen in the data reported in the trials. However, the CDC and the FDA are monitoring the adverse events or side effects as the vaccines are distributed to the public.
There have been reports of a few cases of severe allergic reaction to one of the components of mRNA vaccines and one component in the Johnson & Johnson vaccine. Individuals receiving any of the vaccines should be monitored for 15-30 minutes after injection. If a person has an allergic reaction following the first dose of an mRNA vaccine, they can get the Johnson & Johnson vaccine for their second dose. Additionally, there have been a few reports of blood clots along with low platelet counts after receiving the Johnson & Johnson vaccine. These reports were studied thoroughly. It was determined that these events were rare, and millions of people have been vaccinated without any major issues. Read more on the CDC website.
Should I be worried about experiencing Myocarditis?
Myocarditis, inflammation of the heart, has also been observed in some individuals following receipt of one of the mRNA COVID-19 vaccines. However, these have been rare events—only around 700 out of almost 200 million people who have received at least one dose of the vaccine. Most cases were mild and resolved within a few days after vaccination. Myocarditis is fairly common after viral infections, and the risk of myocarditis is much higher with COVID-19.
How long does immunity last?
It is not known how long immunity will last from the COVID-19 vaccine. In the clinical trials that have been conducted to date, the median length of follow-up was two months for vaccine recipients.
It’s also not known how long immunity from natural infection lasts; there are reports of waning antibody levels around three months after infection, and a few cases of reinfection have been reported. We do know that seasonal coronaviruses (a source for the common cold) do not induce a robust immune response, which leads to limited immunity to these viruses. Research is ongoing, but so far studies have demonstrated real world effectiveness against hospitalization and severe disease with all three authorized vaccines including against the variants. Studies are also underway to look at booster doses, but booster doses for most individuals are not authorized or recommended at this time.
Do I still need to wear a mask and physically distance if I have the vaccine?
Yes! While the vaccines provide protection against COVID-19 disease, it is still possible to become infected and transmit the virus. This means that fully vaccinated individuals may still get COVID-19, although they will be protected against severe disease, hospitalization, and death. In areas with substantial and high transmission, fully vaccinated individuals should wear a mask in public indoor settings to help prevent spread of Delta and protect others. Universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status, is also recommended to allow for full-time in-person learning with proper prevention strategies in place.
If I am vaccinated against COVID-19, can I still spread the virus to others?
Yes! The vaccines are very effective at preventing illness, hospitalizations, and death in those receiving the vaccine. However, data are showing that with the increase in the circulation of the Delta variant, it is possible for people who have been fully vaccinated to get and spread COVID-19. It is extremely important for all individuals to wear masks and distance when in public spaces (schools, work, businesses) in order to prevent spread of the virus to people who have not been vaccinated, most importantly children under age 12.
Can I get the vaccine if I’ve already had COVID-19?
Yes! Data from the clinical trials showed that the vaccines are safe for individuals who were previously infected with SARS-CoV-2.
Who can’t get the vaccine?
Children under age 12 are not eligible to receive the Pfizer-BioNTech vaccine. Those under age 18 are not eligible to receive the Moderna or Johnson & Johnson. Clinical trials have begun to determine safety and efficacy in younger individuals. patients who are pregnant, lactating, or immunocompromised are encouraged to receive the vaccine. No safety issues have been observed in individuals who were pregnant or lactating who also received the vaccine. These patients are recommended to receive the vaccine. There is no evidence that the COVID-19 vaccines interfere with fertility, so individuals interested in having children should get vaccinated.
As with other vaccines, anyone who has a fever or other symptoms may not be able to get the vaccine until their symptoms resolve. This includes those who have symptoms or have tested positive for COVID-19. There is also caution for people with documented anaphylactic reactions to vaccines or who had an allergic reaction to the first dose of COVID-19 vaccine.
Can I get other vaccines, like the flu shot, at the same time as the COVID-19 vaccine?
Yes! Substantial data have shown that the COVID-19 vaccines are safe. The CDC updated its clinical considerations so that COVID-19 vaccines can be given at the same time as other recommended vaccines. This covers both adolescent and adult immunizations. Individuals who are behind in receiving recommended immunizations are encouraged to get caught up on their vaccines to protect themselves from preventable diseases.
If I have allergies, can I get the COVID-19 vaccine?
Yes! Seasonal allergies and even food allergies, including allergies to shellfish and peanuts, do not exclude you from getting the COVID-19 vaccine. Some individuals who have known allergies to any components of the vaccine or a reaction to a first dose of the vaccine should talk to their family doctor as to which vaccine is right for them.
Can I get the COVID-19 vaccine if I am pregnant or breastfeeding?
Individuals who are pregnant or lactating are strongly recommended to get vaccinated against COVID-19. Data have demonstrated that the vaccines are effective and safe for people who are considering pregnancy, are pregnant, or recently pregnant. Vaccination provides protection for both the parent and baby against major issues seen after infection with COVID-19.
How do I report symptoms after the vaccine?
Vaccine recipients should report side effects (called adverse events) to the Vaccine Adverse Event Reporting System (VAERS). This nationwide program collects data to use as signals of unexpected events from a vaccine. If you have a question on what might be considered a side effect related to the vaccine, talk with your family physician.
In addition to VAERS, the CDC implemented a new, smartphone-based tool called v-safe that sends text messages to encourage adverse event reports or impact to quality of life. This system requires a smartphone, and recipients must opt into the system. Information on v-safe is provided to anyone who gets the vaccine, along with a card indicating which vaccine and dose was given, and the EUA fact sheet. Parents will be able to sign up for v-safe on behalf of their child who receives the vaccine.