Recommendations vary based on age, first vaccination received, and time since the last dose.
Coronaviruses are enveloped, nonsegmented, positive-stranded RNA viruses named for their electron microscopic image, which resembles a crown. These viruses typically circulate among animals, such as camels, cats, and bats, but there have been 6 strains that infect humans. Four are responsible for approximately one-third of common colds.1,2
In December 2019, a group of patients with pneumonia of unknown etiology was observed in Wuhan, China, and reported to the World Health Organization (WHO). By the beginning of January 2020, the full genome of a new coronavirus had been sequenced by an expert at the Wuhan Institute of Virology. The virus was initially referred to as “novel coronavirus 2019” (2019-nCoV) by WHO.3 However, on February 11, 2020, it was given the official name of SARS-CoV-2 by the International Committee on Taxonomy of Viruses.4
Coronavirus transmission occurs through person-to person droplets produced by coughing or sneezing, via personal contact, and by touching contaminated surfaces. Since the beginning of the COVID-19 pandemic, efforts have been made to develop and provide acquired immunity against the virus. The first COVID-19 vaccines (produced by Moderna, Inc, and Pfizer Inc) were made available in the United States through emergency use authorization (EUA) in December 2020, then were later granted FDA approval. Currently, there are 4 COVID-19 vaccines in the United States. These vaccines include primary series and boosters. In this article, we will focus primarily on adult indications, efficacy, and safety.
COVID-19 Vaccination Guide
The vaccines available in the United States are effective and reduce the risk of COVID-19, especially severe disease, and they have been associated with substantial reductions in deaths and hospitalizations associated with COVID-19, even in the presence of variants. Hospitalization and mortality rates for COVID-19 have been consistently higher among unvaccinated individuals than vaccinated individuals, with or without booster doses.5
Vaccine recommendations are based on age, the first vaccine received, and the time since the last dose. COVID-19 vaccination is recommended for everyone 6 months of age and older in the United States for the prevention of COVID-19.6,7 There is no FDA-approved or -authorized COVID-19 vaccine for children younger than 6 months of age. Individuals are considered up-to-date with vaccination if they have completed a primary series and received the most recent booster dose recommended for them by the CDC.8
For individuals who are moderately or severely immunocompromised, the recommendations vary and may include a third dose to complete their primary series, as well as 2 booster doses for eligible patients. Specific guidelines for this popu-lation are available on the CDC website.
COVID-19 Vaccine Guidelines
There are 4 different COVID-19 vaccines currently on the market, with 3 different mechanisms of action. Current evidence suggests a preference for messenger RNA (mRNA) vaccines due to their more favorable risk benefit profile, as well as some evidence showing that they may be slightly more efficacious.
mRNA contains instructions that direct cells on how to make proteins and travels into cells through a lipid nanoparticle. Once safely inside, cells read the instruc tions and build antigens against parts of the pathogens. The immune system recognizes these antigens as invaders and responds by producing antibodies and T cells. For COVID-19, mRNA vaccines use genetically engineered mRNA to give cells instructions on how to make the spike protein of the coronavirus, which then works to protect the body from future exposures.
Pfizer-BioNTech has produced a 2-vaccine series called Comirnaty. This monovalent vaccine is approved by the FDA for individuals aged 12 years and older and is available under EUA for children 6 months to 11 years of age.9,10
Moderna has also released a 2-vaccine series and monovalent vaccine (Spikevax). This vaccine is approved by the FDA for individuals aged 18 years and older and is available under EUA for children 6 months to 17 years of age.11,12
Protein Subunit Vaccines
Protein subunit vaccines contain a specific product of the virus to elicit an immune response. A distinguishing feature of coronaviruses is their spikelike proteins on the surface of the molecule, which is what the COVID-19 protein subunit vaccine targets. When patients receive the vaccine, their body recognizes these spike proteins as foreign and exhibits an immune response. Antibodies are then present in the body in case of exposure.
Novavax has produced a 2-vaccine series (Nuvaxovid) that is FDA authorized and available under EUA for individuals aged 12 years or older. This vaccine is not authorized as a primary series for individuals with immunocompromising conditions.13
Viral vector vaccines use a modified version of the virus, or vector, to deliver genetic instructions to cells. The cells then produce antigens, which produces an immune response in the body. The COVID-19 viral vector vaccine targets the spike proteins of coronaviruses.
The Johnson & Johnson (J&J)/Janssen vaccine (Jcovden) is available under EUA for individuals aged 18 years or older, who cannot or elect not to use an mRNA vaccine.14
The efficacy of the COVID-19 vaccines in preventing symptomatic COVID-19 has been shown in several large-scale phase 3 trials. Efficacy varies by manufacturer and age group.
Evidence shows that the Pfizer vaccine is 91% effec-tive at preventing severe disease in individuals aged 16 years and older and 89% effective in preventing symptomatic COVID-19 in individuals with health conditions such as diabetes or obesity.9,10 The Moderna vaccine is 94% effective at preventing severe disease in adults and up to 90% effective in preventing individuals with health conditions from developing symptomatic COVID-19.11,12 The Novavax vaccine is 90% effective at preventing mild, moderate, and severe disease in indi-viduals older than 18 years of age and 79% effective in individuals aged 65 years and older.13 The J&J/Janssen vaccine is 66% effective at preventing severe disease in adults and 85% at preventing the COVID-19 virus with severe illness.14 All 4 vaccines appear to protect against COVID-19 caused by variants.
More than 655 million doses of COVID-19 vaccines have been given in the United States as of November 30, 2022.15 Although COVID-19 vaccine development has been accelerated, each vaccine that has received emergency use listing by WHO (including those that have been authorized or approved in the United States) has gone through the standard preclinical and clinical stages of development.
Adverse effects after COVID-19 vaccination tend to be mild and temporary. In general, the most frequently reported adverse effects after each of the 4 vaccines are injection site pain, fatigue, headache, muscle pain, chills, joint pain, fever, nausea, feeling unwell, and swollen lymph nodes.8,15 Severe allergic reactions after receiving an mRNA COVID-19 vaccine are rare and account for 1 case in 10 million.15 Anaphylaxis data are not available for the J&J/Janssen and Novavax vaccines.
Cardiac complications are rare adverse effects associated with the mRNA vaccines, and patients should be counseled to seek medical attention immediately if they experience chest pain, shortness of breath, or a rapid heart rate.15 Extending the time between the primary series from 3 to 8 weeks may be preferred for young and healthy adults, as that is associated with a lower risk of vaccine-associated myocarditis.15
The viral vector vaccine may potentially increase the risk of thrombosis with thrombocytopenia. Nearly all those affected by this have been women of ages 18 to 49.15 Rarely, some viral vector vaccine recipients may develop Guillain-Barré syndrome, and a potential associ-ation is currently being investigated.16
Contraindications to the COVID-19 vaccine include previous anaphylaxis to a COVID-19 vaccine or to a component of the vaccine.15
The nature of viruses is to evolve over time. Booster doses are subsequent vaccines that are administered to enhance or restore protection that may have waned since primary series vaccination. Bivalent vaccines are updated vaccines that contain the original (ancestral) strain of SARS-CoV-2 and the Omicron BA.4 and BA.5 variants. In the United States, monovalent booster doses are no longer recommended. The bivalent mRNA vaccines are recommended for booster doses.17
The bivalent formulation from Pfizer-BioNTech is authorized as a booster dose for individuals aged 12 years or older. The bivalent formulation from Moderna is authorized as a booster dose for individuals aged 18 years or older.17
An individual is considered up-to-date on their COVID-19 vaccines if they have completed a COVID-19 primary series and received the most recent booster dose recommended by the CDC.
Individuals ages 5 years and older are recommended to receive 1 bivalent mRNA booster dose after completion of any FDA-approved or FDA-authorized monovalent primary series or previously received monovalent booster dose(s).18 This booster recommendation replaces all prior booster recommendations for this age group.
A monovalent Novavax booster dose may be used in limited situations in individuals aged 18 years and older who completed any FDA-approved or FDA-authorized monovalent primary series, have not received any previous booster dose(s), and are unable (ie, contraindicated or not available) or unwilling to receive an mRNA vaccine and would otherwise not receive a booster dose.
COVID-19 vaccines are an important way to keep the body up-to-date with its immune response. Guidance for specific cases or patient populations can be found on the CDC website.
1. Healthcare workers: information on COVID-19. CDC. Updated December 27, 2021. Accessed June 19, 2022. https://www.cdc.gov/coronavirus/2019-nCoV/hcp/index.html
2. Perlman S. Another decade, another coronavirus. N Engl J Med. 2020;382(8):760-762. doi:10.1056/NEJMe2001126
3. WHO Director-General’s remarks at the media briefing on 2019-nCoV on 11 February 2020. News release. World Health Organization. February 11, 2020.Accessed June 19, 2022. https://www.who.int/director-general/speeches/detail/who-director-general-s-remarks-at-the-media-briefing-on-2019-ncov-on-11-february-2020
4. Gorbalenya AE, Baker SC, Baric RS, et al; Coronaviridae Study Group of the International Committee on Taxonomy of Viruses. The species severe acute respiratory syndrome–related coronavirus: classifying 2019-nCoV and naming it SARS-CoV-2. Nat Microbiol.2020;5(4):536-544. doi:10.1038/s41564-020-0695-z
5. Link-Gelles R. Updates on COVID-19 vaccine effectiveness during Omicron. CDC. September 1, 2022. Accessed December 2, 2022. https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2022-09-01/04-COVID-Link-Gelles-508.pdf
6. COVID-19 vaccines for specific groups of people. CDC. Updated June 19, 2022. Accessed December 7, 2022. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/specific-groups.html
7. Farhud DD, Zokaei S. A brief overview of COVID-19 vaccines. Iran J Public Health. 2021;50(7):i-vi. doi:10.18502/ijph.v50i7.6656
8. Overview of COVID-19 vaccines. CDC. Updated November 1, 2022. Accessed December 3, 2022. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/overview-COVID-19-vaccines.html
9. Pfizer-BioNTech COVID-19 vaccines. FDA. Updated December 13, 2022. Accessed November 30, 2022. https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/pfizer-biontech-covid-19-vaccines#additional
10. Fact sheet for healthcare providers administering vaccine (vaccination providers): Pfizer-BioN-Tech COVID-19 vaccine. FDA. Revised December 8, 2022. Accessed November 30, 2022. https://www.fda.gov/media/161327/download
11. Moderna COVID-19 vaccines. FDA. Updated December 15, 2022. Accessed November 30, 2022. https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/moderna-covid-19-vaccines
12. Fact sheet for healthcare providers administering vaccine (vaccination providers): Moderna COVID-19 vaccine. FDA. Revised December 8, 2022. Accessed November 30, 2022. https://www.fda.gov/media/161318/download
13. Fact sheet for healthcare providers administering vaccine (vaccination providers): emergency use authorization (EUA) of the Novavax COVID-19 vaccine, adjuvanted to prevent coronavirus disease 2019 (COVID-19). FDA. Revised October 19, 2022. Accessed December 1, 2022. https://www.fda.gov/media/159897/download
14. Fact sheet for healthcare providers administering vaccine (vaccination providers): emergency use authorization (EUA) of the Janssen COVID-19 vaccine to prevent coronavirus disease 2019 (COVID-19). FDA. Revised May 5, 2022. Accessed December 1, 2022. https://www.fda.gov/media/146304/download
15. Ensuring vaccine safety. CDC. Reviewed July 1, 2020. Accessed November 29, 2022. https://www.cdc.gov/vaccinesafety/ensuringsafety/index.html
16. Woo EJ, Mba-Jonas A, Dimova RB, Alimchandani M, Zinderman CE, Nair N. Association of receipt of the Ad26.COV2.S COVID-19 vaccine with presumptive Guillain-Barré syndrome, February-July 2021. JAMA. 2021;326(16):1606-1613. doi:10.1001/jama.2021.16496
17. CDC statement on ACIP booster recommendations. News release. CDC. September 24, 2021. Accessed December 2, 2022. https://www.cdc.gov/media/releases/2021/p0924-booster-recommendations-.html
18. Stay up to date with COVID-19 vaccines including boosters. CDC. Updated December 9, 2022. Accessed November 30, 2022. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/stay-up-to-date.html
About the Author
Joanna Lewis, PharmD, MBA, is the 340B compliance coordinator at Baptist Health in Jacksonville, Florida.