The 2023–2024 COVID-19 Vaccines: What ACIP Recommended and Why

On September 12, 2023, the CDC's Advisory Committee on Immunization Practices (ACIP) voted 13 to 1 to recommend an updated COVID-19 vaccine for everyone aged 6 months and older. This page summarizes the MMWR report of that decision (later corrected by an erratum, whose figures are used here), written by Joanna J. Regan, Megan Wallace and colleagues.

This describes the recommendation for the 2023–2024 season. The report itself said it would be reviewed as new evidence or new vaccines arrived; check CDC for current guidance.

Why a new vaccine

COVID-19 vaccines had prevented an estimated 18.5 million hospitalizations and 3.2 million deaths in the United States by the end of 2022. But the virus kept evolving and protection waned. The bivalent mRNA vaccines recommended since September 2022 targeted variants no longer circulating widely; by September 2, 2023, XBB-sublineage variants made up more than 99% of sequenced U.S. samples.

The updated vaccines are monovalent, built on the Omicron XBB.1.5 variant, to broaden immunity against the XBB variants then circulating, including against severe illness and death.

Who was still at risk

• Oldest and youngest. Adults 65 and older and infants under 6 months had the highest hospitalization rates. From January 1 to August 26, 2023, adults 75 and older were hospitalized at two to three times the rate of those 65–74; infants under 6 months at about the rate of 65–74-year-olds.
• Healthy children too. Among children hospitalized with COVID-19 from January to June 2023, 23% of those aged 5–11 and 34% of those aged 12–17 had no underlying condition. From January 2022 to June 2023, half of those 17 and under who died during a COVID-19 hospitalization had none.
• Long COVID. Symptoms lasting 3 months or more ranged from under 1% of people under 18 to 5% of those aged 35–49. In June 7–19, 2023, about one in four adults with post-COVID conditions reported significant limits on their activities.
• Unequal burden. Racial and ethnic minority groups remained disproportionately hospitalized. As of May 10, 2023, only 17% of Americans had had a bivalent dose, with lower coverage in some minority groups.

Hospitalizations had begun rising again in mid-July 2023, with more expected over fall and winter.

Deaths with COVID-19 as the underlying cause on the death certificate.

The evidence

ACIP has held 37 public meetings on COVID-19 vaccines since June 2020, supported by a work group that met weekly. It graded the evidence on the bivalent vaccine used from September 2022 to April 2023 with the GRADE method — the closest guide to what the new vaccine could be expected to do — and weighed it in its Evidence to Recommendations framework, along with cost, values, acceptability, feasibility and equity.

Effectiveness in adolescents and adults (bivalent vaccine, pooled observational data):

For children there were too few data, so benefits were inferred from older age groups, with very low certainty.

Waning. In adults 65 and older without immune compromise, effectiveness against hospitalization fell from 67% at 7–59 days after a bivalent dose to 28% at 120–179 days. Against emergency and urgent care visits, it fell from 59%–63% to 36%–47% by 60–119 days across ages 5–17, 18–64 and 65 and older. Protection against the most severe outcomes — ventilation, intensive care, death — held up better. Effectiveness has historically been lower and waned faster in people with weakened immune systems.

Safety. Anaphylaxis ran at about 4.8 per million Pfizer-BioNTech doses and 5.1 per million Moderna doses. Myocarditis and pericarditis occur mainly in adolescent and young adult males — up to 188 per million after a Pfizer-BioNTech monovalent booster in males aged 16–17 — and are less common after boosters than after the initial series, and with longer gaps between doses. Severe short-term reactions were more common with vaccine than placebo in trials.

Manufacturers' data showed the XBB vaccines from Moderna, Novavax and Pfizer-BioNTech raised immune responses against the circulating variants.

Cost. At an assumed $120 a dose, vaccination saves money in adults 65 and older. It cost an estimated $25,787 per quality-adjusted life year at ages 50–64 and $115,588 at ages 18–49, where the estimate was more sensitive to assumptions. There were no estimates yet for children.

The recommendations

The recommendation covered the updated Moderna, Novavax and Pfizer-BioNTech vaccines, used within their FDA licensing or EUA. It was interim for children 6 months–11 years and for Novavax, since those were under EUA.

Ages 5 and older, not immunocompromised: one updated mRNA dose, whatever the earlier history. With Novavax (12 and older), two doses 3–8 weeks apart if never vaccinated, otherwise one. Anyone previously vaccinated waits at least 8 weeks after the last dose.

Ages 6 months–4 years, not immunocompromised:

Moderately or severely immunocompromised:

• Unvaccinated, 6 months–11 years: three doses of the same updated mRNA vaccine.
• Unvaccinated, 12 and older: three mRNA doses of the same brand, or two Novavax.
• One or two earlier mRNA doses: one or two more, depending on how many.
• Three or more earlier mRNA doses: one.
• Earlier Novavax or Janssen (Johnson & Johnson), 12 and older: one updated dose of any brand.
• Additional doses at a provider's discretion, at least 2 months apart.

Paying for it

The vaccines moved from federal purchase to the commercial market in fall 2023. Under the Affordable Care Act and the CARES Act, most insurers must cover them without cost sharing; Medicare Part B covers them, nearly all Medicaid enrollees pay nothing, and the Vaccines for Children Program, serving about half of Americans under 19, provides them free. The temporary Bridge Access Program served uninsured and underinsured adults through health clinics and pharmacies. Providers give the EUA fact sheet or package insert and explain expected side effects before vaccinating.

Any clinically significant reaction should be reported to the Vaccine Adverse Event Reporting System at vaers.hhs.gov or 1-800-822-7967, even when it is unclear the vaccine caused it.

Sources

Based on Regan JJ, Moulia DL, Link-Gelles R, et al., "Use of Updated COVID-19 Vaccines 2023–2024 Formula for Persons Aged ≥6 Months: Recommendations of the Advisory Committee on Immunization Practices — United States, September 2023," MMWR, Centers for Disease Control and Prevention (with its erratum); a work of the United States government in the public domain.