2023-2024 Flu Season

Key information

Updates to the Advisory Committee on Immunization Practices (ACIP) Flu Vaccine Recommendations for the 2023-2024 season

A couple of things are different for the 2023-2024 influenza (flu) season.

The composition of flu vaccines has been updated. Flu vaccines for the U.S. 2023-2024 season will contain the following:

Egg-based vaccines

• an A/Victoria/4897/2022 (H1N1)pdm09-like virus; (Updated)
• an A/Darwin/9/2021 (H3N2)-like virus;
• a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
• a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Cell- or recombinant-based vaccines

• an A/Wisconsin/67/2022 (H1N1)pdm09-like virus; (Updated)
• an A/Darwin/6/2021 (H3N2)-like virus;
• a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
• a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
• These recommendations include one update compared to the 2022-2023 U.S. flu vaccine composition. The influenza A(H1N1)pdm09 vaccine virus component was updated for egg-based and cell- or recombinant-based flu vaccines.

People with egg allergy may get any vaccine (egg-based or non-egg-based) that is otherwise appropriate for their age and health status. Previously, it was recommended that people with severe allergy to egg (those who have had any symptom other than hives with egg exposure) be vaccinated in an inpatient or outpatient medical setting. Beginning with the 2023-2024 season, additional safety measures are no longer recommended for flu vaccination of people with an egg allergy beyond those recommended for receipt of any vaccine, regardless of the severity of previous reaction to egg. All vaccines should be given in settings where allergic reactions can be recognized and treated quickly.

Projected U.S. flu vaccine supply for the 2023-2024 season

• Vaccine manufacturers have projected that they will supply the United States with as many as 156.2 million to 170 million doses of influenza vaccines for the 2023-2024 season. These projections may change as the season progresses.
  • All flu vaccines for the 2023-2024 season will be quadrivalent (four-component).
  • Most will be thimerosal-free or thimerosal-reduced vaccines (91%), and about 21% of flu vaccines will be egg-free.
• The latest information on total distribution of influenza vaccine doses for the 2023-2024 season is available.

Updates to U.S. flu surveillance methods for the 2023-2024 season

Starting with the 2023-2024 influenza season, the percentage of deaths with influenza listed on the death certificate will be displayed in FluView. P&I (pneumonia and/or influenza) no longer measures the impact of influenza in the same way it had prior to the COVID-19 pandemic, and the PIC (pneumonia, influenza and/or COVID) measure is largely being driven COVID-19 activity making it difficult to monitor the impact of influenza using that measure. Although monitoring influenza-only coded deaths will underestimate the full impact of influenza mortality, this measure allows for tracking trends in the impact of influenza on mortality and is not as influenced by COVID-19 as the other two measures.

Getting your flu vaccine for free or at low cost

Most health care insurance plans cover the annual flu shot as preventive care. Flu vaccination is often available at no or low cost to people who do not have insurance.

For Children

• If your child is insured, most health care insurance plans cover flu vaccination at no cost to you. Check that your provider takes your child's insurance.
• Flu vaccine is also available at no costA to you through CDC's Vaccines for Children (VFC) Program. A child must qualify for this program.
• The VFC program serves children through 18 years of age who meet at least one of the following criteria:
  • American Indian or Alaska Native (AI/AN)
  • Medicaid-eligible
  • Uninsured
  • Underinsured
• If your child is not insured, ask your child's doctor if they are a VFC provider or you can contact your state or local health department to find a VFC provider.

For Adults

• If you have insurance, your flu vaccine will be at no cost to you. Check that your provider takes your insurance.
• If the insurance does not cover flu vaccine or it has a fixed dollar limit or cap for vaccines, there may be options for no-cost or low-cost flu vaccination.
• If you don't have insurance, there may be options for no-cost or low-cost flu vaccination.

Where can you go for no-cost or low-cost vaccines:

• Your health provider
• Pharmacies
• Health Resources & Services Administration (HRSA) supported health centers
• Employers, schools, and community organizations

B/Yamagata and flu vaccines summary

Quadrivalent flu vaccines protect against four different influenza viruses: one H1N1 virus, one H3N2 virus, one B/Victoria virus and one B/Yamagata virus. All current flu vaccines in the United States are quadrivalent vaccines. For many years, these four kinds of viruses circulated most commonly among people. However, CDC and global surveillance data show that B/Yamagata lineage viruses have not been detected since March 2020. Because these B/Yamagata viruses are not actively circulating in people, the risk of infection with B/Yamagata lineage viruses is considered to be low at this time.

These surveillance data were reviewed by the World Health Organization Influenza Vaccine Composition Advisory Committee (September 29, 2023) and the U.S. FDA Vaccines and Related Biological Products Advisory Committee (VRBPAC) (October 5, 2023). Based on these data, these committees recommended that B/Yamagata lineage antigens be removed from flu vaccines for use in the United States and internationally as soon as reasonably possible.

The same data was presented to the CDC Advisory Committee on Immunization Practice (ACIP) on October 26, 2023. CDC is not involved in regulatory decision-making, including for flu vaccines, but will make a recommendation on the use of flu vaccine for 2024-2025 season once VRBPAC has selected the viruses for inclusion in U.S. 2024-2025 flu vaccines. In the meantime, CDC will continue to conduct surveillance to track circulating influenza viruses, including whether any B/Yamagata viruses are detected.

U.S. quadrivalent flu vaccines for the 2023-2024 (current) season include B/Yamagata lineage viruses. The exact timing for removal of B/Yamagata lineage components from flu vaccines has not yet been decided.

Trivalent versus quadrivalent vaccines

Trivalent flu vaccines are formulated to protect against three flu viruses (an A(H1N1) virus, an A(H3N2) virus, and a B/Victoria virus). Trivalent flu vaccines are approved for use in many countries. Both trivalent and quadrivalent flu vaccines are expected to offer similar protection against the flu viruses they protect against. B/Yamagata flu viruses have not circulated in the population since March 2020, so protection from trivalent and quadrivalent flu vaccines is expected to be similar. All flu vaccines for the 2024-2025 season are anticipated to be trivalent in the United States.

Coinfection: Getting more than one respiratory illness at the same time

It is possible to get sick with more than one respiratory virus at the same time. This includes being sick with flu and COVID-19. It is also possible to be sick with multiple flu viruses, like influenza A and B, at the same time.

Flu, RSV, and COVID-19 coinfection data: 2023-2024 season

One way CDC collects data on coinfections with influenza and other respiratory viruses (including SARS-CoV-2, the virus that causes COVID-19, and respiratory syncytial virus, or RSV) is by using data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) which is part of the Respiratory Virus Surveillance Network (RESP-NET).

FluSurv-NET collects coinfection data among children and adults hospitalized with laboratory-confirmed flu, COVID-19, and RSV at affiliated acute care hospitals in 14 states. The following table provides preliminary data on coinfections reported in FluSurv-NET for October and November. The table provides the total number of COVID-19 and flu coinfections as well as the total number of flu and RSV coinfections reported during this time frame among patients hospitalized with laboratory-confirmed influenza virus infection. It also shows the percentages of flu and COVID-19 coinfections as well as flu and RSV coinfections among people hospitalized with laboratory-confirmed influenza virus infection during this time period.

*Note: Information in this table represents preliminary FluSurv-NET data from persons admitted during October-November 2023. These estimates are preliminary and subject to change.

No cases of coinfection with all three viruses (influenza virus, SARS-CoV-2, and RSV) were reported from the Respiratory Virus Surveillance Network (RESP-NET) during October-November 2023.