COVID-19 Vaccine, 2023-2024 Formula (Comirnaty, Spikevax)
By William Elliott, MD, FACP, and James Chan, PharmD, PhD
Dr. Elliott is Assistant Clinical Professor of Medicine, University of California, San Francisco.
Dr. Chan is Associate Clinical Professor, School of Pharmacy, University of California, San Francisco.
The FDA has authorized for emergency use (EUA) the updated COVID-19 vaccine for 2023-2024.1 These monovalent vaccines are formulated to more closely target currently circulating variants.1 The vaccines are Comirnaty and Spikevax.
The latest vaccines are active immunizations to prevent COVID-19. The vaccines are approved for patients age 12 years and older. The EUA allows injections for patients age 6 months to 11 years.
Administer a single intramuscular dose of 0.5 mL (Spikevax) or 0.3 mL (Comirnaty).1 Patients age 5 years and older, regardless of previous vaccination, are eligible to receive a single dose. Patients age 6 months to 4 years who have been vaccinated can receive one or two doses (timing and number of doses to administer depends on the previous COVID-19 vaccine received. Unvaccinated patients age 6 months through 4 years are eligible to receive three doses of Comirnaty or two doses of Spikevax. For patients who have been vaccinated, administer the 2023-2024 formulation at least two months after the last dose. Vaccines are available as single-dose vials. Each contains 50 mcg (Comirnaty) or 30 mcg (Spikevax) of a nucleoside-modified messenger RNA (mRNA) encoding the viral spike glycoprotein of SARS-CoV-2 omicron variant linage XBB.1.5.2,3 Those who have recently contracted a COVID-19 infection should delay vaccination for at least three months.4
Vaccines are formulated to closely target circulating variants to provide protection against serious disease leading to hospitalization and death.1 The newest vaccines target XBB.1.5, which is no longer the dominant circulating variant, but they offer protection against XBB.1.16 and more distant variants (e.g., EG.5.1, FL.1.1.1, and BA.2.86).5
Common adverse reactions are pain at injection site, fatigue, headache, chills, muscle pain, joint pain, and fever.2,3 Post-marketing data with authorized or approved mRNA COVID-19 vaccines indicates patients can be at higher risks of developing myocarditis and pericarditis, particularly within the first week following vaccination. For Spikevax, the observed risk is highest in men age 18 to 24 years.3 For Comirnaty, the observed risk is highest in men age 12 to 17 years.2 Some of these cases may require intensive care support; however, most patients seem to resolve symptoms with conservative management.2,3
The latest vaccines elicit an immune response to the spike glycoprotein of SARS-CoV-2. The previously approved bivalent vaccine elicited neutralizing antibody responses against omicron (including BA.4 and BA.5) and the original Wuhan strain. The updated formulation targets the currently circulating and more distant variants.
The 2023-2024 vaccine is no longer referred to as a “booster.” The bivalent COVID-19 vaccines are no longer authorized for use in the United States. Scientists anticipate the composition of COVID-19 may need to be updated annually, similar to the seasonal influenza vaccine.1
1. U.S. Food & Drug Administration. FDA takes action on updated mRNA COVID-19 vaccines to better protect against currently circulating variants. Sept. 11, 2023.
2. Pfizer-BioNTech. Comirnaty prescribing information. September 2023.
3. Moderna. Spikevax prescribing information. September 2023.
4. Centers for Disease Control & Prevention. Interim clinical considerations for use of COVID-19 vaccines in the United States. COVID-19 vaccination and SARS-CoV-2 infection. Page last reviewed Sept. 15, 2023.
5. Tin A, Moniuszko S. FDA and CDC sign off on new COVID vaccines. Here’s what to know about the updated shots for fall 2023. CBS News. Sept. 15, 2023.
The newest vaccines target XBB.1.5, which is no longer the dominant circulating variant, but they offer protection against XBB.1.16 and more distant variants (e.g., EG.5.1, FL.1.1.1, and BA.2.86).
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