COVID-19 vaccines provide protection against COVID-19, the infection caused by the SARS-CoV-2 virus. Vaccination remains the most effective strategy to prevent severe illness and death from SARS-CoV-2 infection.
There are multiple COVID-19 vaccines currently in use worldwide.
(See also Overview of Immunization and COVID-19.)
Preparations of COVID-19 Vaccine
There are 2 SARS-CoV-2 virus (COVID-19) mRNA vaccines for COVID-19 used in the United States.There are 2 SARS-CoV-2 virus (COVID-19) mRNA vaccines for COVID-19 used in the United States.
The mRNA vaccines do not contain viral antigen but rather deliver a small, synthetic piece of mRNA that encodes for the desired target antigen (the spike protein). After being taken up by cells of the immune system, the vaccine mRNA degrades after instructing the cell to produce viral antigen. The antigen is then released and triggers the desired immune response to prevent severe infection upon subsequent exposure to the actual virus.
There is 1 SARS-CoV-2 virus (COVID-19) recombinant spike protein nanoparticle vaccine for COVID-19 used in the United States.There is 1 SARS-CoV-2 virus (COVID-19) recombinant spike protein nanoparticle vaccine for COVID-19 used in the United States.
The spike protein vaccine contains a recombinant form of the SARS-CoV-2 spike protein, which then triggers the desired immune response.
Indications for COVID-19 Vaccine
The mRNACOVID-19 vaccines are indicated for the prevention of infection caused by SARS-CoV-2 virus. Guidance on COVID-19 vaccination has evolved over time; various expert bodies have issued differing recommendations. See Centers for Disease Control and Prevention (CDC), American Academy of Pediatrics (AAP), and American Academy of Family Physicians (AAFP) for specific recommendations and further information.
Contraindications and Precautions for COVID-19 Vaccine
Contraindications for COVID-19 vaccines are the following:
Severe allergic reaction after a previous dose of any vaccine
Severe allergic reaction to a vaccine component
Precautions for COVID-19 vaccines include the following:
Acute anaphylactic reaction immediately after a dose
Immunocompromise, including due to immunosuppressant therapy
Moderate or severe illness, with or without fever
History of multisystem inflammatory syndrome in children (MIS-C) or multisystem inflammatory syndrome in adults (MIS-A)
History of myocarditis or pericarditis within 3 weeks after a dose of any COVID-19 vaccine
Appropriate medical treatment to manage immediate allergic reactions must be immediately available in the event an acute anaphylactic reaction occurs after any COVID-19 vaccine is administered. COVID-19 vaccine recipients should be monitored for immediate adverse reactions.
Immunocompromised people, including those receiving immunosuppressant therapy, may have a diminished immune response to these vaccines.
The U.S. Food and Drug Administration (FDA) has issued a warning regarding reports of myocarditis and pericarditis after administration of COVID-19 vaccines, suggesting there may be an increased risk of these events after vaccination (1). The observed risk is highest in young males. Vaccine recipients should seek medical attention right away if they have chest pain, dyspnea, tachycardia, or palpitations after vaccination. Although some people have required intensive care, data from short-term follow-up studies suggest that symptoms usually resolved with conservative management.
Contraindications and precautions reference
1. CDC. Clinical Considerations: Myocarditis and Pericarditis after Receipt of COVID-19 Vaccines Among Adolescents and Young Adults. October 2023.
Dose and Administration of COVID-19 Vaccine
For COVID-19 vaccinations available for use in the United States, all dose and administration information for all age groups and people with special conditions is available from the CDC, AAP, and AAFP (1–3).
COVID-19 vaccine doses should be administered by the intramuscular route.
Dose and administration references
1. Centers for Disease Control and Prevention (CDC). Advisory Committee on Immunization Practices (ACIP) Recommendations. Accessed September 23, 2025.
2. American Academy of Pediatrics (AAP). AAP Immunization Schedule. Accessed September 23, 2025.
3. American Academy of Family Physicians (AAFP). COVID-19 Vaccine: Fall 2025-26 Immunization Recommendations. Accessed September 23, 2025.
Adverse Effects of COVID-19 Vaccine
The COVID-19 vaccines all have similar adverse effects.
Rare, severe allergic reactions, including anaphylaxis, have been reported.
Other adverse effects are common and may include:
Injection site pain, swelling, and erythema
Fatigue
Headache
Muscle and joint pains
Fever and chills
Nausea and vomiting
Malaise
Lymphadenopathy
Adverse effects tend to last for several days.
Reactive lymphadenopathy may occur after COVID-19 vaccination and may result in a false-positive reading on mammography (1). Multiple studies have been performed, and routine screening mammography should not be delayed after COVID vaccination (2, 3).
For more information about adverse effects of these vaccines, refer to the prescribing information.
Adverse effects references
1. Lamb LR, Mercaldo SF, Carney A, Leyva A, D'Alessandro HA, Lehman CD. Incidence, Timing, and Long-Term Outcomes of COVID-19 Vaccine-Related Lymphadenopathy on Screening Mammography. J Am Coll Radiol. 2024;21(9):1477-1488. doi:10.1016/j.jacr.2024.02.032
2. Hao M, Edmonds CE, Nachiappan AC, Conant EF, Zuckerman SP. Management Strategies for Patients Presenting With Symptomatic Lymphadenopathy and Breast Edema After Recent COVID-19 Vaccination. AJR Am J Roentgenol. 2022;218(6):970-976. doi:10.2214/AJR.21.27118
3. Zhang M, Ahn RW, Hayes JC, Seiler SJ, Mootz AR, Porembka JH. Axillary Lymphadenopathy in the COVID-19 Era: What the Radiologist Needs to Know. Radiographics. 2022;42(7):1897-1911. doi:10.1148/rg.220045
More Information
The following English-language resources may be useful. Please note that The Manual is not responsible for the content of these resources.
Advisory Committee on Immunization Practices (ACIP): ACIP Recommendations: COVID-19 Vaccine
Centers for Disease Control and Prevention (CDC): Coronavirus Disease 2019 (COVID-19) Vaccine Safety
American Academy of Pediatrics (AAP): Recommended Child and Adolescent Immunization Schedule for Ages 18 Years or Younger
American Academy of Family Physicians (AAFP): COVID-19 Vaccine: Fall 2025-26 Immunization Recommendations
European Centre for Disease Prevention and Control (ECDC): Coronavirus Disease (COVID-19): Recommended vaccinations
