Trivalent Influenza Vaccines Are Readied for Fall

Although influenza season often peaks in the winter months, influenza activity can continue as late as May.¹ Since the COVID-19 pandemic, the timing and severity of influenza seasons have been unpredictable, so pharmacists should remain aware of current vaccination guidelines—in addition to the recent recommendation for trivalent vaccines from the FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC).²

Image credit: Leigh Prather | stock.adobe.com

The CDC’s Advisory Committee on Immunization Practices (ACIP) releases yearly recommendations that provide updated guidance for the use of seasonal influenza vaccines. Typically released in late August, the guidance aims to update the previous year’s recommendations and ensure that best practices for influenza vaccination are followed by all health care professionals.

ACIP’s 2023-2024 influenza vaccination guidance maintained the same recommendation that has been central to the group’s guidance since 2010: All persons 6 months and older without any medical contraindications should receive the seasonal influenza vaccine when available.³

Vaccination is not recommended until after the summer months, to avoid the possibility of waning immunity. This is an especially important consideration for groups such as adults 65 years and older and pregnant persons in the first or second trimester. However, some populations should receive an influenza vaccine as early as possible, especially some children aged 6 months through 8 years and pregnant persons in the third trimester.³

ACIP does not recommend a specific influenza vaccine. However, guidance for individuals 65 years and older specifies that they should ideally receive a higher-dose or adjuvanted influenza vaccine. These options include the quadrivalent high-dose inactivated influenza vaccine (HD-IIV4), quadrivalent recombinant influenza vaccine (RIV4), or quadrivalent adjuvanted inactivated influenza vaccine (allV4).³

The ACIP provided 2 key updates to the 2022-2023 influenza recommendations. First, the composition of the 2023-2024 seasonal influenza vaccines included an update to the influenza A(H1N1)pdm09 component. The vaccines contain an influenza A/Victoria/4897/2022 (H1N1)pdm09-like virus for egg-based vaccines or an influenza A/Wisconsin/67/2022 (H1N1)pdm09-like virus for cell culture–based and recombinant vaccines, an influenza A/Darwin/9/2021 (H3N2)-like virus for egg-based vaccines or an influenza A/Darwin/6/2021 (H3N2)-like virus for cell culture–based and recombinant vaccines, an influenza B/Austria/1359417/2021 (Victoria lineage)–like virus, and an influenza B/Phuket/3073/2013 (Yamagata lineage)–like virus, according to the guidance published in Morbidity and Mortality Weekly Report.³

Second, ACIP recommended that persons older than 6 months with an egg allergy receive an influenza vaccine with no restrictions. This differs from previous guidance, which recommended that those with an egg allergy be vaccinated in an inpatient or outpatient medical center and observed by a health care provider. Instead, according to the new recommendations, persons with an egg allergy can be vaccinated with any influenza vaccine, regardless of whether it is egg based.³

Co-Occurring Respiratory Virus Seasons

During influenza season, the threat of other diseases remains, including respiratory syncytial virus (RSV). RSV is the leading cause of hospitalization among infants in the US, underscoring the importance of staying aware of recommended guidelines. In its 2023 report, ACIP recommended Abrysvo (Pfizer) for pregnant persons at 32 to 36 weeks’ gestation using seasonal administration to prevent RSV in infants.⁴

Additionally, ACIP has continued to recommend nirsevimab-alip (Beyfortus; Sanofi) in infants to prevent RSV-associated lower respiratory tract infection. In addition to nirsevimab, palivizumab (Synagis; Sobi) is recommended for some children under age 24 months with certain preconditions that put them at a greater risk for severe RSV.⁵

Trivalent Influenza Vaccines

Reviewing vaccination guidelines for influenza and RSV is especially timely considering VRBPAC’s announcement that US influenza vaccines should be trivalent in the 2024-2025 season and include A(H1N1), A(H3N2) and B/Victoria-lineage viruses. Quadrivalent influenza vaccines have been standard in the US since the 2013-2014 influenza season, when a second influenza B virus strain was added to the vaccine to protect the public from both lineages of influenza B viruses. Prior to the availability of quadrivalent vaccines, trivalent vaccines were the norm for 35 influenza seasons.²

However, the influenza B/Yamagata virus strain has been undetected in global surveillance systems since March 2020. This has made its inclusion in the seasonal influenza vaccine unnecessary, according to the FDA.²

One potential reason for the extinction of the Yamagata lineage of influenza B is the implementation of public health measures designed to control the spread of COVID-19.⁶ Because the strain has not been isolated since March 2020, the incorporation of social distancing, masking, and restrictions on large gatherings into daily life could have led to its extinction.

“[The] FDA has been engaging and interacting with manufacturers of FDA-approved seasonal flu vaccines and providing scientific and regulatory advice to them to facilitate the timely availability of approved safe and effective trivalent seasonal flu vaccines for the 2024-2025 US flu season. [The] FDA anticipates that there will be an adequate and diverse supply of approved trivalent seasonal flu vaccines for the United States in the coming season,” FDA officials said in a statement.²

Switching to trivalent vaccines has the added benefit of increasing current production capacity of influenza vaccines. Each year, approximately 700 million doses of trivalent vaccines could be produced, vs 500 million doses of quadrivalent vaccines if that were to remain the standard, according to research published in Viruses.⁶

Because vaccine distribution is consistently hindered due to production shortages, “any means of increasing production capacity would be of enormous benefit, as influenza continues to cause millions of infections, hundreds of thousands of deaths, and billions of dollars lost due to health care costs and loss of working days,” the researchers said.⁶

Pharmacists and clinicians should remain vigilant for future guidance as well as information on when to expect trivalent vaccines to be manufactured and delivered to vaccination settings. The decision to receive a vaccine is sometimes difficult for a person to make; it is critical that treatment providers be educated and can provide up-to-date recommendations depending on the situation.

Additionally, since the COVID-19 pandemic, the prevalence of vaccine hesitancy and misinformation has increased, especially through social media and other settings where there is a lack of accurate, fact-based information.⁷ This makes it even more imperative that pharmacists ready themselves to answer questions and ease concerns among those who may be hesitant to receive an influenza vaccine.

References

1. Flu season. CDC. Updated September 20, 2022. Accessed March 31, 2024. https://www.cdc.gov/flu/about/season/index.html

2. Use of trivalent influenza vaccines for the 2024-2025 US influenza season. FDA. March 5, 2024. Accessed March 31, 2024. https://www.fda.gov/vaccines-blood-biologics/lot-release/use-trivalent-influenza-vaccines-2024-2025-us-influenza-season

3. Grohskopf LA, Blanton LH, Ferdinands JM, Chung JR, Broder KR, Talbot HK. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices – United States, 2023-24 influenza season. MMWR. 2023;72(2):1-25. doi:10.15585/mmwr.rr7202a1

4. Fleming-Dutra KE, Jones JM, Roper LE, et al. Use of the Pfizer respiratory syncytial virus vaccine during pregnancy for the prevention of respiratory syncytial virus-associated lower respiratory tract disease in infants: recommendations of the Advisory Committee on Immunization Practices – United States, 2023. MMWR. 2023;72(41):1115-1122. doi:10.15585/mmwr.mm7241e1

5. RSV immunization for children 19 months and younger. CDC. September 28, 2023. Accessed March 31, 2024. https://www.cdc.gov/vaccines/vpd/rsv/ public/child.html

6. Vajo Z, Torzsa P. Extinction of the influenza B Yamagata line during the COVID pandemic—implications for vaccine composition. Viruses. 2022;14(8):1745. doi:10.3390/v14081745

7. Zhang V, Zhu P, Wagner AL. Spillover of vaccine hesitancy into adult COVID-19 and influenza: the role of race, religion, and political affiliation in the United States. Int J Environ Res Public Health. 2023;20(4):3376. doi:10.3390/ijerph20043376