What to expect during the 2024-2025 flu season | Image Credit: © Sherry Young - © Sherry Young - stock.adobe.com.

According to the CDC, more than 44,900 people died from influenza complications during the 2023-2024 flu season. As it does every year, the CDC recommends everyone 6 months or older receive the updated flu vaccine, with rare exceptions.¹ But this year, the influenza vaccine is different from the one last season: COVID-19 has become a major player alongside influenza, and patients may be asking about a new virus strain. Read on for the latest information.

Change from quadrivalent to trivalent vaccines

In March 2024, the FDA recommended influenza virus strains with a trivalent vaccine composition for use in the upcoming 2024-2025 flu season; last season, a quadrivalent vaccine was used. These trivalent seasonal influenza vaccines include 2 influenza A viruses (H1N1) and 1 influenza B virus.

The FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) recommended that the trivalent formulation of egg-based influenza vaccines contain the following²:

• an A/Victoria/4897/2022 (H1N1)pdm09–like virus;
• an A/Thailand/8/2022 (H3N2)–like virus; and
• a B/Austria/1359417/2021 (B/Victoria lineage)–like virus.

For the trivalent formulation of cell- or recombinant-based influenza vaccine, the committee recommended the following²:

• an A/Wisconsin/67/2022 (H1N1)pdm09–like virus;
• an A/Massachusetts/18/2022 (H3N2)–like virus; and
• a B/Austria/1359417/2021 (B/Victoria lineage)–like virus.

As to which strain might be more severe, Jane M. Carnazzo, MD, FAAP, a pediatrician with Children’s Physicians in Omaha, Nebraska, noted, “Typically, influenza A is more severe than influenza B, but there [have] been years where I’ve seen B just as virulent as A. This year, it’s kind of anybody’s guess.”

Why the change from the quadrivalent to the trivalent formulation for this season? “One of the strains that had been circulating—the B/Yamagata—has been dormant since 2020,” explained Rebecca Snead, RPh, senior director, strategic initiatives and long-term care division, at the National Community Pharmacists Association. “[VRBPAC], back in October 2023, had signaled that since the strain has been dormant, perhaps we could drop it because there’s no sense in getting vaccinated against something that is not being seen. So, we’re going back to the trivalent [composition], which has historically always been the flu vaccine.”

But, Snead added, some challenges may lie ahead when it comes to public messaging. “Some people might not understand the messaging and think because we are going from a quadrivalent to a trivalent vaccine, that maybe the flu is not so bad now,” she explained. “I think as health care providers, we need to be educated and tell our patients that the trivalent vaccine is what is needed to protect the public, and it is absolutely full protection.”

There is also a nasal spray vaccination option, but that comes with its own brand of skepticism. “Often with children, the nasal spray vaccine, which is a live attenuated vaccine, works better than the shot,” Carnazzo said. “But I have heard people say, ‘Oh, I got the [nasal spray] vaccine, and then I got flu, so I never got the vaccine again.’ It’s important to let patients know that they cannot get the flu from the nasal spray. Because it’s an attenuated live vaccine, there is a small chance of getting a little nasal congestion or something like that, but they won’t get influenza from it.”

How COVID-19 affects flu season

COVID-19 has permanently changed the landscape of flu season. Today, preparing for this highly contagious period means getting vaccinated for both viruses. “This year is going to be the first season where the COVID-19 vaccines are going to be available [when] or very soon after the flu vaccine is available,” Snead said. “And we can begin conditioning the American public to get their COVID-19 vaccine as well, just like every other respiratory virus vaccine.”

Following its Advisory Committee on Immunization Practices meeting in June, the CDC recommended both the updated 2024-2025 COVID-19 vaccine and the updated 2024-2025 flu vaccine to prevent severe cases of COVID-19 and influenza this fall and winter.¹

When should patients be vaccinated?

Snead, who has spoken with manufacturers of this year’s vaccines, said, “There should be ample supply and very timely access to influenza vaccines this year. There are not any unexpected hiccups at this point. Typically [the vaccines] start arriving in early August.”

When should the public expect to get their vaccine? “Timing [is] something we as pharmacists need to keep in mind,” Snead explained. “If you [as a pharmacist] get the vaccine in late July or August, go ahead and vaccinate pregnant people in their third trimester to help them and to protect the baby."

Added Carnazzo, “For [those of] us in pediatrics, you get them when you can get them. Vaccinating patients from mid-September to mid-October is the sweet spot.”

And don’t forget individuals who have had a solid organ transplant. “They need a higher dose of the vaccine. There is a higher concentration of vaccination for this population group, and it’s important that they get vaccinated as well,” Carnazzo said.

The bird flu question

Avian influenza, also called bird flu, has been on the public radar since April 2024, when an individual in Texas became the first human infected with novel avian influenza A(H5N1).³ Since then, additional cases have been confirmed in multiple US states, although the CDC’s human health risk assessment for the public remains low.

Although public risk is low, the World Health Organization “is operating in a constant state of readiness for a potential influenza pandemic,” said Maria Van Kerkhove, PhD, head of epidemic and pandemic preparedness and prevention at the World Health Organization, in an article published in Nature.⁴

At the time of publication, there have been only 9 cases of avian influenza in the US this year: 4 following exposures to dairy cows, and 5 following exposures to poultry.⁵ “Right now, the bird flu is still considered to be an extremely low risk. It is being monitored very closely,” Snead said. “But this is a question that pharmacists may get asked when they are administering the flu vaccine: ‘Will this protect me against bird flu?’ And the answer is no. However, the United States has invested in developing a vaccine for the bird flu, just in case it becomes necessary. But it’s not a worry at this point.”

Editor’s note: This article was originally published by our sister publication Drug Topics.

A previous version of this article stated "Children 18 years and younger need 2 doses, so if you have the vaccine early, and you have a child and parent in your pharmacy, you want that child to [receive] that first dose of the flu vaccine in August," however, it should be "children 6-months through 8-years-old (up to their 9th birthday) need 2 doses of the Flu vaccine the first year they receive it."

References:

1. CDC recommends updated 2024-2025 COVID-19 and flu vaccines for fall/winter virus season. News release. CDC. June 27, 2024. Accessed July 8, 2024. https://www.cdc.gov/media/releases/2024/s-t0627-vaccine-recommendations.html

2. Use of trivalent influenza vaccines for the 2024-2025 U.S. influenza season. FDA. March 5, 2024. Accessed July 8, 2024. https://www.fda.gov/vaccines-blood-biologics/lot-release/use-trivalent-influenza-vaccines-2024-2025-us-influenza-season

3. Health alert: first case of novel influenza A(H5N1) in Texas, March 2024. Texas Health and Human Services. April 1, 2024. Accessed July 15, 2024. https://www.dshs.texas.gov/news-alerts/health-alert-first-case-novel-influenza-h5n1-texas-march-2024

4. Mallapaty S. Bird flu could become a human pandemic: how are countries preparing? Nature. July 12, 2024. Accessed July 15, 2024. https://www.nature.com/articles/d41586-024-02237-4

5. H5 bird flu: current situation. CDC. Updated July 26, 2024. Accessed July 16, 2024. https://www.cdc.gov/bird-flu/situation-summary/index.html