On December 11, 2020, the US Food and Drug Administration (FDA) issued an emergency use authorization (EUA) for the first vaccine against COVID-19, the Pfizer-BioNTech COVID-19 vaccine.1 This announcement was quickly followed by EUAs of the Moderna COVID-19 vaccine on December 18, 2020, and the Johnson & Johnson COVID-19 vaccine on February 27, 2021.2,3

Most mass vaccination sites and clinics offer 1 to 2 types of COVID-19 vaccines and give adult patients the choice of which vaccine they prefer to receive. In mid-December 2021, the Centers for Disease Control and Prevention (CDC) endorsed the updated recommendation by the Advisory Committee on Immunization Practices (ACIP) that individuals receive a messenger RNA (mRNA) COVID-19 vaccine over the Johnson & Johnson COVID-19 vaccine, citing the latest evidence on vaccine effectiveness, vaccine safety, and rare adverse events.4,5

When counseling patients on vaccine decisions, factors to consider include patient age, underlying medical conditions, contraindications, and vaccine availability.6,7 Health care providers should be informed about all available vaccines to help guide individualized treatment decisions. The bottom line is that receiving any vaccine is better than not being vaccinated; the best vaccine for an individual is the one that the patient will accept and has no contraindications to.

mRNA Vaccines

Pfizer-BioNTech and Moderna vaccines are mRNA vaccines. The Pfizer-BioNTech vaccine (Comirnaty®) received full FDA approval on August 23, 2021, for persons aged 16 years and older and is authorized under EUA for persons 5 to 15 years of age8; it is the only vaccine that is authorized for use for children and adolescents.9 The FDA is awaiting further immunogenicity and safety data before granting Pfizer-BioNTech full approval for this younger age group.10

The Pfizer-BioNTech vaccine dose for patients aged 5 to 11 years is lower than the standard dose for those aged 12 years and older (10 µg vs 30 µg). The EUA formulation of the Pfizer-BioNTech COVID-19 vaccine is the same as the fully licensed Comirnaty vaccine, and both formulations can be used interchangeably for persons aged 16 years and older.11

Moderna received EUA in the US for adults aged 18 years and older. The dose is the same for persons of all ages for whom the vaccine is indicated.

Both mRNA vaccines are highly effective in preventing serious outcomes of COVID-19, including severe disease, hospitalization, and death. In clinical trials, the 2-dose Moderna vaccine series was 94.1% effective at preventing COVID-19 disease in patients aged 18 years and older.12 The 2-dose Pfizer-BioNTech series was 95% effective at preventing COVID-19 disease in people aged 16 years and older and greater than 90% effective in children aged 5 to 15 years.13

A large observational study comparing the effectiveness of the mRNA vaccines in a real-world setting found slightly higher COVID-19 outcomes (ie, infection, hospital or intensive care unit [ICU] admission, and death) with the Pfizer-BioNTech vaccine than with the Moderna vaccine during periods when the Alpha or Delta variants were predominantly found. The study authors noted that the risk for these outcomes was low regardless of the vaccine received and that safety was not assessed in this study.14

Adenovirus Vector Vaccine

The Johnson & Johnson COVID-19 vaccine is an adenovirus vector vaccine. Although it is authorized under EUA for persons aged 18 years and older, the CDC now recommends initial vaccination with an mRNA COVID-19 vaccine. The recommendation is based on a rare but increased incidence of thrombosis with thrombocytopenia (TTS) in patients given the Johnson & Johnson COVID-19 vaccine.4,5 This serious adverse event occurs at a rate of approximately 3.83 cases per million Johnson & Johnson COVID-19 vaccine doses.5 The Johnson & Johnson COVID-19 vaccine is also associated with an increased risk for immune thrombocytopenia (ITP) during the first 42 days following vaccination. Patients with a history of ITP may require platelet monitoring following vaccination.5

Initially, only 1 dose of this vaccine was indicated to be considered fully vaccinated against COVID-19. Recent studies revealed that the immune response (66%) was not as robust as that seen in earlier data following 1 dose.4,5 Currently, CDC recommendations call for a booster with either mRNA vaccine rather than another dose of the Johnson & Johnson COVID-19 vaccine because of the risk for TSS.5

Counseling Before COVID-19 Vaccines and Boosters

It is important that clinicians advise patients and parents regarding expected side effects of any of the COVID-19 vaccines.  Side effects include swelling, redness, and pain at the injection site; fever; headache; tiredness; muscle pain; chills; and nausea. Vaccinated individuals may experience any or all of the expected side effects or they may experience no side effects. Informing individuals of the potential for side effects helps decrease anxiety should these expected side effects occur.

Patients should also be counseled to take either ibuprofen or acetaminophen for any discomfort following immunization and to contact their health care provider if any symptoms do not resolve in a few days or if redness and swelling at the injection site worsen. According to the CDC, ibuprofen or acetaminophen should not be taken before vaccination because it is not known how these medications may affect how well the vaccine works. Antihistamines should not be taken before a COVID-19 vaccine to prevent allergic reactions.15

Comfort measures such as cold compresses to the injection site and encouraging fluids should be discussed. Patients and parents should also be advised to seek immediate medical care by calling 911 if they are having or think they might be having a severe allergic reaction after leaving the vaccination site.15

Additionally, COVID-19 and influenza vaccines (as well as routine childhood immunizations) can be administered at the same time. The CDC recommends separating injection sites by 1 inch or more or administering the vaccines in different limbs.

Safety Profile of mRNA Vaccines

The Pfizer-BioNTech and Moderna vaccines have excellent safety profiles. However, rare events — including myocarditis and pericarditis — have been noted with both vaccines. The CDC continues to keep track of rare side effects related to the COVID-19 vaccines through several monitoring systems, including the Vaccine Adverse Event Reporting System (VAERS), Vaccine Safety Datalink (VSD), Clinical Immunization Safety Assessment (CISA) Project, and v-safe after vaccine health checker.

In a study by Witberg et al, 54 cases of myocarditis were diagnosed among more than 2.5 million persons who received at least 1 dose of the Pfizer-BioNTech vaccine.16 The authors noted that myocarditis was a rare side effect with an estimated incidence of 2.13 cases per 100,000 persons who received at least 1 dose of vaccine. The highest incidence of myocarditis was 10.69 cases per 100,000 persons reported in male patients aged 16 to 29 years. Most cases of myocarditis were mild or moderate in severity.16 In a second study of more than 5 million people who had received the Pfizer-BioNTech COVID-19 vaccine, 136 developed myocarditis.17

Myocarditis has been identified as a possible side effect of the Moderna vaccine as well. Although several large US surveillance studies indicate comparable rates of myocarditis after either mRNA vaccine, an analysis of data from the VSD showed an excess of 9.7 cases per million doses of the Moderna vs the Pfizer-BioNTech vaccine among a subgroup of patients aged 18 to 39 years.18 These data were based on 14 myocarditis cases that occurred within 7 days of dose 2 of the Moderna vaccine and 12 cases with the Pfizer-BioNTech vaccine; none of the patients required ICU admission. In another study, a total of 1439 cases of myocarditis/myopericarditis among approximately 151.1 million mRNA-1273 vaccine recipients were reported to the Moderna global safety database. The overall reporting rate among all vaccine recipients was 0.95 cases per 100,000 vaccine recipients; the observed rate was highest — 7.40 cases per 100,000 recipients — among men aged 18 to 24 years.19

In general, reported cases of myocarditis or pericarditis after COVID-19 vaccination are mild, self-limiting, and resolve with conservative treatment.16,19 The important take-home message is that there is a greater chance of developing myocarditis from COVID-19 than from the vaccine. Approximately 150 cases of myocarditis occur per 100,000 patients infected with COVID-19 disease.20

Contraindications to COVID-19 Vaccines

All patients who are candidates for COVID-19 vaccines should be screened for possible contraindications. Contraindications to the Pfizer-BioNTech and Moderna vaccines include anaphylaxis, angioedema affecting the airway, and Stevens-Johnsons syndrome after a previous dose or to a component of the COVID-19 vaccine or known diagnosed allergy to a component of the COVID-19 vaccine. If a patient has an allergy to polyethylene glycol, mRNA vaccines should not be administered. If a patient has an allergy to polysorbate, the Johnson & Johnson COVID-19 vaccine should not be administered. However, people with contraindications to mRNA COVID-19 vaccines may be able to receive the Johnson & Johnson COVID-19 vaccine and vice versa, provided certain measures are taken such as a thorough risk assessment for TTS and allergic reactions and the presence of appropriate medical care if anaphylaxis occurs.21 

In addition, patients who developed TTS following receipt of the Johnson & Johnson COVID-19 vaccine (or other COVID-19 vaccines not currently authorized in the US that are based on adenovirus vectors) should not receive this vaccine as a booster dose.21 Should the Johnson & Johnson COVID-19 vaccine be the vaccine of choice, recipients must be informed of the risks and benefits of this vaccine.5

Underlying Conditions

Although everyone 5 years of age and older should receive a COVID-19 vaccine primary series as soon as possible, vaccination is extremely important for patients with medical conditions that increase the risk for severe illness from COVID-19 infection. These conditions include cancer, chronic kidney disease, chronic lung diseases, dementia or other neurologic diseases, diabetes (type 1 or type 2), Down syndrome, heart disease, HIV, immunocompromised conditions, mental health conditions, obesity, pregnancy, sickle cell disease or thalassemia, smoking (current or former), solid organ or blood stem cell transplant, stroke or cerebrovascular disease, substance use disorders, and tuberculosis.6

The following is a list of immunocompromising conditions that constitute an increased risk for COVID-19 disease complications7:

  • Active treatment for solid tumor and hematologic malignancies
  • Receipt of solid-organ transplant and taking immunosuppressive therapy
  • Receipt of CAR-T-cell or hematopoietic stem cell transplant (within 2 years of transplantation or taking immunosuppressive therapy)
  • Moderate or severe primary immunodeficiency (eg, DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced or untreated HIV infection
  • Active treatment with high-dose corticosteroids (ie, ≥20 mg/d prednisone or equivalent), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor-necrosis factor (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory

Individuals who are moderately or severely immunocompromised may not mount a robust immune response to vaccines and need a third primary dose if they received either of the mRNA vaccines. For the Pfizer-BioNTech vaccine, the third dose is indicated 28 days after the second shot for individuals 5 years of age and older. For the Moderna vaccine, the third dose is indicated 28 days after the second dose in adults 18 years of age and older.6,7

Receipt of Non-FDA-Approved COVID-19 Vaccines Outside of the US

Patients who were vaccinated outside of the US and completed all of the recommended doses of a COVID-19 vaccine listed for emergency use by the World Health Organization that is not FDA approved or authorized are considered fully vaccinated 2 weeks after completion of the series.21 Individuals who received only 1 such vaccine do not need to restart their primary vaccination series and should receive a single dose of the Pfizer-BioNTech COVID-19 vaccine at least 28 days after their first dose to be considered fully vaccinated.

Individuals vaccinated outside of the US who received a COVID-19 vaccine that is not listed for emergency use by the WHO should restart their primary vaccination series with an FDA-approved or FDA-authorized COVID-19 vaccine, preferably an mRNA COVID-19 vaccine, after a minimum interval of at least 28 days following receipt of the last dose of the original vaccine.21

All of these patients should receive booster shots at CDC-recommended intervals.

COVID-19 Booster Shots

Booster shots are a recent update to the CDC vaccination paradigm. Data indicate that although COVID-19 vaccines are highly effective, vaccine effectiveness wanes over time. Booster and additional primary vaccine doses increase protection against COVID-19. It is essential to advise patients and parents that boosters are a vital part of the continued protection against COVID-19 disease for individuals 12 years of age and older.

For adults, the recommended timing of the booster dose for both the Pfizer-BioNTech and Moderna vaccines has been reduced from 6 months to 5 months after receiving the final dose in the primary vaccine series.22,23 Pfizer-BioNTech is the only booster shot authorized for children aged 12 to 17 years.24 Individuals 18 years of age and older can receive either the Pfizer-BioNTech or the Moderna booster. In adults, either mRNA vaccine may be given as a booster regardless of which vaccine was given for the primary series.25

A booster is also recommended for all patients who received the Johnson & Johnson COVID-19 vaccine 2 months after the first shot. Either the Pfizer-BioNTech or the Moderna booster dose is recommended over a second dose of the Johnson & Johnson COVID-19 vaccine in most patients because of a rare but increased risk for TTS.5

Booster doses of the Pfizer-BioNTech and the Johnson & Johnson vaccines are the same as the initial vaccine doses; the Moderna booster dose (50 µg) is half that used in the initial vaccine series (100 µg).


Vaccines are the most effective tool available to prevent hospitalization and death from COVID-19. As patients and parents trust the advice provided by their health care providers, educating them on the most current evidence-based information on available COVID-19 vaccines can affect their decisions to accept or reject immunization.26 Health care providers should encourage every patient who is medically able to be vaccinated.

Mary Koslap-Petraco, DNP, PPCNP-BC, CPNP, FAANP, is clinical assistant professor at Stony Brook School of Nursing in Stony Brook, NY, and pediatric nurse practitioner and owner of Pediatric Nurse Practitioner House Calls.


1. Ernst D. Pfizer. BioNTech COVID-19 vaccine gets EUA; first doses shipped. MPR. December 14, 2020. Accessed January 5, 2022.

2. Ernst D. FDA panel recommends EUA for Moderna’s COVID-19 vaccine. MPR. December 18, 2020. Accessed January 5, 2022.

3. Fortner A, Schumacher D. First COVID-19 vaccines receiving the US FDA and EMA emergency use authorization. Discoveries. 2021;9(1):e122. doi:10.15190/d.2021.1

4. CDC endorses ACIP’s updated COVID-19 vaccine recommendations. News release. Centers for Disease Control and Prevention; December 16, 2021. Accessed January 5, 2022. https://www.cdc.gov/media/releases/2021/s1216-covid-19-vaccines.html

5. Johnson & Johnson’s Janssen COVID-19. Vaccine overview and safety. Centers for Disease Control and Prevention. December 28, 2021. Accessed January 5, 2022.  https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/janssen.html

6. People with certain medical conditions. Centers for Disease Control and Prevention. December 14, 2021. Accessed January 5, 2022. https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/people-with-medical-conditions.html

7. COVID-19 vaccines for moderately or severely immunocompromised people. Centers for Disease Control and Prevention. December 14, 2021. Accessed January 5, 2022. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/immuno.html

8. FDA approves first COVID-19 vaccine. News release. US Food and Drug Administration; August 23, 2021. Accessed January 5, 2022. https://www.fda.gov/news-events/press-announcements/fda-approves-first-covid-19-vaccine 

9. Ernst D. FDA panel votes in favor of Pfizer-BioNTech COVID-19 vaccine for 5 to 11 year-olds. MPR. October 26, 2021. Accessed January 5, 2022.

10. Pfizer and BioNTech provide update on ongoing studies of COVID-19 vaccine. News release. Pfizer; December 17, 2021. https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-provide-update-ongoing-studies-covid-19

11. Pfizer and BioNTech initiate rolling submission of supplemental biologics license application to U.S. FDA for booster dose of COMIRNATY® in individuals 16 and older. News release. Pfizer; August 21, 2021. https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-initiate-rolling-submission

12. Moderna COVID-19 vaccine overview and safety. Centers for Disease Control and Prevention. December 14, 2021. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Moderna.html

13. Pfizer-BioNTech COVID-19 vaccine (also known as Comirnaty) overview and safety. Centers for Disease Control and Prevention. January 6, 2022. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Pfizer-BioNTech.html

14. Dickerman BA, Gerlovin H, Madenci AL, et al. Comparative effectiveness of BNT162b2 and mRNA-1273 vaccines in U.S. veterans. N Engl J Med. 2021:NEJMoa2115463. doi:10.1056/NEJMoa2115463

15. When to call the doctor. Centers for Disease Control and Prevention. December 1, 2021. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/expect/after.html

16. Witberg G, Barda N, Hoss S, et al. Myocarditis after Covid-19 vaccination in a large health care organization. N Engl J Med, 2021;385(23):2132-2139. doi:10.1056/NEJMoa2110737

17. Mevorach D, Anis E, Cedar N, et al. Myocarditis after BNT162b2 mRNA vaccine against Covid-19 in Israel. N Engl J Med. 2021;385(23):2140-2149. doi:10.1056/NEJMoa2109730

18. Klein N. Myocarditis analyses in the Vaccine Safety Datalink: rapid cycle analyses and “head-to-head” product comparisons. October 20, 2021. Accessed January 5, 2022. https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2021-10-20-21/08-COVID-Klein-508.pdf

19. Straus W, Urdaneta V, Esposito DB, et al. Myocarditis after mRNA-1273 vaccination: a population-based analysis of 151 million vaccine recipients worldwide. medRxiv preprint. 2021.11.11.21265536; doi:10.1101/2021.11.11.21265536

20. Boehmer TK, Kompaniyets L, Lavery AM, et al. Association between COVID-19 and myocarditis using hospital-based administrative data — United States, March 2020–January 2021. MMWR Morb Mortal Wkly Rep. 2021;70:1228-1232. doi:10.15585/mmwr.mm7035e5

21. Interim clinical considerations for use of COVID-19 vaccines currently approved or authorized in the United States. Centers for Disease Control and Prevention. December 23, 2021. Accessed January 5, 2022. https://www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html#Contraindications

22. CDC recommends Pfizer booster at 5 months, additional primary dose for certain immunocompromised children. News release. Centers for Disease Control and Prevention; January 4, 2022. Accessed January 5, 2022. https://www.cdc.gov/media/releases/2022/s0104-Pfizer-Booster.html

23. FDA shortens interval for booster dose of Moderna COVID-19 vaccine to five months. News release. US Food and Drug Administration; January 7, 2022. Accessed January 8, 2022. https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-shortens-interval-booster-dose-moderna-covid-19-vaccine-five-months

24. Aboulenein A, Banerjee A. US FDA authorizes Pfizer’s COVID-19 booster for 12- to 15-year olds. News release. Reuters; January 3, 2022. https://www.reuters.com/business/healthcare-pharmaceuticals/us-fda-clears-pfizers-covid-19-booster-shot-12-15-year-olds-2022-01-03/

25. Fast HE, Zell E, Murthy BP, et al. Booster and additional primary dose COVID-19 vaccinations among adults aged ≥ 65 years — United States, August 13, 2021–November 19, 2021. MMWR Morb Mortal Wkly Rep. 2021;70(50):1735-1739. doi:10.15585/mmwr.mm7050e2

26. Nguyen KH, Yankey D, Lu P, et al. Report of health care provider recommendation for COVID-19 vaccination among adults, by recipient COVID-19 vaccination status and attitudes — United States, April–September 2021. MMWR Morb Mortal Wkly Rep. 2021;70(50):1723-1730. doi:10.15585/mmwr.mm7050a1