Influenza key points

Healthcare providers and local public health departments are instrumental in preventing and controlling the spread of influenza in Massachusetts. Here are some important updates for this year:

2024-2025 Recommendation Highlights

Influenza Activity During the 2023-2024 Influenza Season

The 2023-24 influenza season in the United States was considered moderately severe with an estimate of at least 34-75million symptomatic illnesses, 15-33 million medical visits, 380,000-900,000 hospitalizations, and 17,000-100,000 deaths caused by influenza virus infection.

The predominant influenza virus throughout the 2023-24 influenza season was influenza A(H1N1 pdm09); however, as activity declined, A(H3N2) and B/Victoria viruses began circulating at higher proportions than A(H1N1 pdm09) viruses. Most influenza viruses tested were in the same genetic subclade as, and antigenically similar to the vaccine reference viruses included in the season’s influenza vaccine. All the influenza viruses collected and tested for antiviral resistance by CDC since October 1, 2023 were susceptible to zanamivir, and peramivir and the majority (>99.7%) were susceptible to oseltamivir, peramivir, zanamivir and baloxivir.

The 2023-24 season was more similar to those seen prior to the COVID-19 pandemic than what was observed in the two seasons immediately after the emergence of SARS-CoV-2 (2020-2021 and 2021-2022). The peak percentage of specimens testing positive for influenza (18.3%) as reported to CDC from clinical laboratories nationally was slightly less than the peak percentage positive (26.5%) during the five influenza seasons (2015-16 – 2019-20) immediately preceding the COVID-19 pandemic. Similarly, the cumulative rate of influenza-associated hospitalizations as reported in FluSurv-NET this season was higher than the hospitalization rates for all pre-COVID seasons except for 2017-2018.Mortality attributed to influenza this season also was similar to the 2022–2023 influenza season and to what was seen in the most recent pre-COVID seasons. From October 1, 2023, to August 31, 2024, the number of death certificates with influenza listed as an underlying or contributing cause of death during the 2023-24 season (10,289). The weekly percentage of deaths due to influenza ranged from 0.03% to 1.3% and peaked during the week ending January 6, 2024 (week 1). (Influenza deaths began to increase in late November 2023, peaking in early January 2024 (week 1), and then declined. This peak occurred later in the season compared to the 2022–2023 influenza season, which peaked at 1.6% during mid-December 2022; however, it was slightly earlier than recent pre-COVID influenza seasons, which peaked between late January 2018 (2017–2018 season) and mid-March 2016 (2015–2016 season). While the peak weekly percentage of deaths due to influenza was lower during this season compared to last, the cumulative percentage of deaths due to influenza was slightly higher (0.4% during 2023–2024 compared with 0.3% during 2022–2023) due to longer duration of elevated influenza-associated mortality.

The number of pediatric deaths reported this season (205) exceeds the previous record of 199 deaths reported during the 2019-2020 season.

For the first time since the COVID-19 pandemic, the timing of peak influenza activity occurred within the range of what was expected based on pre-COVID-19 activity (more than 80% of seasons between 1997–98 and 2019–20 peaked between late December and late February), and activity returned to low levels by mid-May. During the 2022–2023 season, influenza activity peaked earlier than expected (early December) and the 2021–2022 season continued longer than expected (through mid-June).

Recommendations

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2024-25 Influenza Season has been published. CDC recommends annual influenza vaccination for everyone 6 months and older who do not have contraindications. 

What’s New for 2024-2025

• The composition of the 2024-25 U.S. seasonal influenza trivalent vaccines includes an update to the influenza A(H3N2) component and a removal of influenza B Yamagata as there have been no confirmed global detections of B/Yamagata since March 2020.
• Regarding influenza vaccination of persons with egg allergy, ACIP recommends that all persons aged ≥6 months with egg allergy should receive influenza vaccine. Any influenza vaccine (egg based or nonegg based) that is otherwise appropriate for the recipient’s age and health status can be used. It is no longer recommended that persons who have had an allergic reaction to egg involving symptoms other than urticaria should be vaccinated in an inpatient or outpatient medical setting supervised by a health care provider who is able to recognize and manage severe allergic reactions if an egg-based vaccine is used. Egg allergy alone necessitates no additional safety measures for influenza vaccination beyond those recommended for any recipient of any vaccine, regardless of severity of previous reaction to egg. All vaccines should be administered in settings in which personnel and equipment needed for rapid recognition and treatment of acute hypersensitivity reactions are available.
• Consistent with prior guidance, everyone 6 months and older should get a flu vaccine, ideally by the end of October. Flu vaccination is especially important for people who are at higher risk of developing serious flu complications, like those with certain chronic health conditions and people 65 years and older. 
• Solid organ transplant recipients aged 18 through 64 years who are receiving immunosuppressive medication regimens may receive either HD-IIV3 or aIIV3 as acceptable options.
• More information about the 2024-2025 flu season is available at Key Facts about Seasonal Flu Vaccine
• For more information on this year’s flu recommendations, see: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2024–25 Influenza Season
• For detailed guidance about influenza and influenza vaccination for providers, see the CDC’s Flu Website for Healthcare Professionals 
• For new and noteworthy influenza-related developments and feature stories by influenza season, visit the CDC’s Flu News and Spotlights page. 
• See: CDC’s Key Facts about Seasonal Flu Vaccine
• See: Frequently Asked Influenza Questions 2024-2025 Season
• See: Influenza Antiviral Medications: Summary for Clinicians
• Also, see FluView Interactive and Respiratory Illnesses Data Channel
• There are some websites that help providers and patients locate vaccines:
• Flu and COVID-19 vaccine locations 

Find out where you can get a flu vaccine by asking your primary care provider, going to a local pharmacy, or visiting Vaccines.gov for a site near you.

Influenza disease burden

Despite the lower levels of influenza during the pandemic, the overall burden of disease is great. CDC estimates that influenza has resulted in between 9 million and 41 million illnesses, between 100,000 and 710,000 hospitalizations and between 4,900 and 51,000 deaths annually between 2010 and 2023.

Preliminary in-season estimates of influenza burden in the United States for the 2023-24 season are that influenza virus infection resulted in 34-75 million symptomatic illnesses, 15-33 million medical visits, 380,000-900,000 hospitalizations, and 17,000-100,000 deaths.

CDC posts preliminary estimates of the influenza disease burden. Every year influenza vaccines are updated to better match circulating viruses.

Your strong recommendation is important!

A health care provider’s strong recommendation is a critical factor affecting whether your patient gets influenza vaccine. Patients listen to providers when providers strongly recommend vaccination.

• There are many misconceptions about flu vaccine.  CDC addresses many of these   misconceptions and provides a summary of the benefits of vaccination and selected scientific studies that support these benefits.

Flu vaccine is recommended for everyone 6 months of age and older who do not have contraindications. While some flu formulations are not recommended for some patients and some patients should not receive flu vaccine at all, this is uncommon. For more guidance on contraindications and precautions for influenza vaccine, please see the CDC MMWR article detailing the 2024-25 ACIP Influenza Recommendations.

Below are the links to the latest information and data that might inform your conversations with patients in the upcoming months: 

• Flu vaccine offers the best protection against flu-related illness, hospitalization, and death. Flu vaccine reduces this burden of illness.
• For the latest information about vaccine effectiveness, see CDC Seasonal Flu Vaccine Effectiveness Studies.
• Influenza vaccination was found to reduce deaths in children. A study in Pediatrics was the first of its kind to show that influenza vaccination is effective in preventing influenza-associated deaths among children. A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.  And a 2020 study found that during the 2018-2019 flu season, flu vaccination reduced flu-related hospitalization by 41% and flu-related emergency department visits by half among children (aged 6 months to 17 years old).
• Influenza vaccination may make illness milder. While some people who get vaccinated may develop influenza, vaccination may make their illness milder. A 2017 study in Clinical Infectious Diseases (CID) showed that influenza vaccination reduced deaths, intensive care unit (ICU) admissions, ICU length of stay, and overall duration of hospitalization among hospitalized influenza patients. A 2021 published study found that in a primarily older population, influenza vaccination was associated with a 41% reduction in risk of hospitalized influenza illness. Journal of Infectious Diseases.

Influenza vaccination has been found effective in preventing influenza-associated hospitalization during pregnancy. For more information on influenza associated hospitalizations, please see the latest MMWR.

For more information on questions and answers related to this flu season, please see the General information about flu page.  

Vaccine supply

DPH universally provides influenza vaccine, as well as other routinely recommended vaccines, to all children through 18 years of age. DPH only provides influenza vaccine for uninsured adults seen at public sites. For more information on state-supplied vaccine, please see the Vaccine Management page. 

Nationally, manufacturers have projected they will provide as many as 148 million doses of flu vaccine this season. All flu vaccines for the 2024-2025 season will be trivalent (three-component). Most will be thimerosal free or thimerosal reduced vaccine (94%), and about 20% of flu vaccines will be egg-free. Information about the national vaccine supply can be found at Vaccine Supply & Distribution Information for Health Care Providers | Influenza (Flu) | CDC  website. 

The Immunization Action Coalition (IAC) has a very helpful table of the Influenza Vaccine Products for the 2024-2025 Influenza Season. 

When to vaccinate

For most persons who need only one dose of influenza vaccine for the season, vaccination should ideally be offered during September and October. However, vaccination should continue throughout the season, as long as influenza viruses are circulating. The duration of the influenza season varies from, year to year and influenza activity might not occur in certain communities until February or March. In New England, flu activity usually lasts until April and May.

To avoid missed opportunities, providers should continue to offer vaccination during routine health care visits and hospitalizations.

Safe influenza vaccine administration

CDC provides comprehensive vaccine administration resources, including Vaccine Administration eLearn at their Vaccine Administration website

Vaccine information statement

The most recent versions of Vaccine Information Statements (VISs) for Influenza Vaccines (IIV and LAIV4) for use this season are dated 8-06-21. The latest versions of all the VISs can be found at this site.

Resources

2024-2025 Influenza Season – Fall Vaccination Clinics

• CDC pdf – Checklist of Best Practices for Vaccine Clinics
• DPH vaccination clinic guidelines

Centers for Disease Control and Prevention

• Influenza Main Website 
• Influenza website for Healthcare Providers: Influenza (Flu) Health Professionals 
• Frequently Asked Influenza (Flu) Questions: 2024-2025 Season 
• Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2024-25 Influenza Season
• Resources for Mass Vaccination Clinics: 
  • Planning for Mass clinics
  • Includes sections on: 
    • Planning activities
    • Pre-clinic activities
    • During the clinic activities
    • Post-clinic activities
  • A checklist of Best Practices for Vaccination Clinics Held at Satellite, Temporary, or Off-site Locations, and other useful material 
  • Clinic Supplies Check List is a comprehensive list that can be adapted for many settings.
  • Antiviral Summary for Clinicians 

Immunization Action Coalition

• Model Standing Orders: 
  • Administering Influenza Vaccine to Adults (PDF)
  • Administering Influenza Vaccine to Children and Teens (PDF)
  • Medical Management of Vaccine Reactions in Adults in a Community Setting 
  • Medical Management of Vaccine Reactions in Children and Teens in a Community Setting 
• Screening Forms: 
  • Screening Checklist for Contraindications to Inactivated Injectable Influenza Vaccination (PDF)
  • Screening Checklist for Contraindications to Live Attenuated Intranasal Influenza Vaccination (PDF)
• Flu Products Chart:
  • Influenza Vaccine Products for the 2024–2025 Influenza Season 

HealthMap

• VaccineFinder Find out where you can get a flu vaccine by visiting vaccines.gov/flu

American Academy of Pediatrics

• Recommendations for Prevention and Control of Influenza in Children, 2024-2025

American College of Physicians

• Adult Immunizations 

American Academy of Family Physicians

• Family Doctor 

American College of Obstetricians and Gynecologists

• Immunization for Women  

Children’s Hospital of Philadelphia

• Vaccine Education Center 
• Influenza 
• Vaccine Safety Website 

DPH

• mass.gov/influenza 
• DPH Immunization Division webpage for healthcare and public health professionals
• Flu Information for School Administrators and Childcare Professionals
• Influenza Fact Sheet  

Date published:	December 16, 2024