Vaccine Info

Influenza Vaccines

Authored by
Last reviewed
March 26, 2024

Influenza Vaccines Dosage, News, Side Effects, Usage

Influenza vaccines, known as flu shots, protect people against viruses that research indicates will be the most common each year. However, every flu season is different, and each influenza virus can affect people differently, according to the U.S. Centers for Disease Control and Prevention (CDC), the European Medicines Agency (EMA), and the World Health Organization (WHO). The WHO has prequalified quadrivalent influenza vaccine manufacturers in 2024 and says that influenza vaccines do not cause seasonal flu since they are made with either killed or weakened viruses. Four different groups of influenza viruses infect humans, and influenza vaccines are manufactured differently and have various indications as licensed by the U.S. Food and Drug Administration (FDA). According to the CDC, most will be thimerosal-free or thimerosal-reduced vaccines (91%), and about 21% of flu vaccines will be egg-free.

Influenza Vaccine Formulations 2024-2025

The U.S. FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) met on March 5, 2024, and finalized the quadrivalent and trivalent influenza vaccines flu shot options for 2024-2025. On October 5, 2023, the VRBPAC unanimously voted to remove the influenza B/Yamagata component from influenza vaccines produced for the Southern Hemisphere's flu season. As of March 2024, the FDA is working with influenza vaccine manufacturers to make trivalent vaccines available. Sanofi has said it could offer trivalent shots if there is a definitive switch from quadrivalent shots. As of March 6, 2024, CSL Seqirus received FDA approval for its U.S. trivalent influenza vaccines and anticipates delivering its flu shots for the 2024-2025 flu season.

The WHO recommended on February 23, 2024, that trivalent vaccines for use in the 2024-2025 northern hemisphere influenza season contain the following:  Egg-based vaccines - 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. Cell culture- or recombinant-based vaccines: 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. For quadrivalent egg- or cell culture-based or recombinant vaccines for use in the 2024-2025 northern hemisphere influenza season, the WHO recommends the inclusion of the following as the B/Yamagata lineage component: a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Flu Shot Availability 2024

Depending upon jurisdiction, physicians, nurses, and pharmacists can choose from up to nine different influenza vaccines for the 2023-2024 flu season. The CDC's Weekly Influenza Vaccination Dashboard shares preliminary weekly flu vaccination data.

As of March 2024, the U.S. CDC reported about 158 million flu vaccines had been distributed during the 2023-2024 season. The CDC said that 173 million influenza vaccines had been distributed during the 2022-2023 flu season and 194 million during the 201-2022 season. According to a report by the Global Healthy Living Foundation and IQVIA, about 60% of vaccinations during the 2022 flu season took place at pharmacies in the U.S. The MiU.Sary Health System also updates the Seasonal Influenza Resource Center regarding flu shots for the 2023-2024 season. Private manufacturers produce flu shots, so the annual supply depends on those companies.

The WHO Immunization, Vaccines, and Biologicals team (MI4A) publishes vaccine-specific market studies, analyzing global demand and supply prospects for individual vaccines. On January 30, 2024, an updated Global Market Study was posted.

Six months and older:

Afluria is an inactivated influenza vaccine for active immunization against influenza disease caused by subtypes A and B.

Fluarix is prepared from influenza viruses propagated in embryonated chicken eggs.

Flulaval is a quadrivalent, split-virion, inactivated influenza vaccine from a virus propagated in the allantoic cavity of embryonated hens' eggs.

Fluzone Quadrivalent and trivalent inactivated vaccine prevents influenza disease caused by influenza A subtype viruses and type B viruses.

Flucelvax Quadrivalent is a cell culture-based flu vaccine that protects against four flu virus strains. Its revenue recently increased by 30%.

Two-49 years of age:

FluMist is an Intranasal, live quadrivalent vaccine containing four vaccine virus strains.

Eighteen years and older:

Flublok is made without the use of eggs. Therefore, it is not subject to the mutations sometimes introduced into the vaccine during egg adaptation, which can cause traditional vaccines to be ineffective. In addition, Flublok contains ns three times the antigen of standard-dose inactivated influenza vaccines.

Sixty-five years and older:

Fluad is an inactivated, quadrivalent influenza virus antigen produced in eggs, and MF59C.1 is an oil-in-water emulsion adjuvant.

Fluzone High-Dose contains four times the antigen of standard-dose inactivated influenza vaccines.

Influenza Vaccine Effectiveness 

Anthony C. Fries, Ph.D., with the U.S. DoD, presented 'Influenza Surveillance and Mid-Season Vaccine Effectiveness' at the U.S. FDA Vaccines and Related Biological Products Advisory Committee meeting on March 5, 2024. The DOD calculated the Beneficiary VE for the 2023-2024 Mid-Season Influenza Estimates, which ranged from 43% to 53%.

A meta-analysis of flu vaccine effectiveness (VE) studies conducted from 2017 through 2022 and published in the journal Vaccines on February 28, 2024, shows real-world effectiveness of seasonal influenza vaccination averaged 41.4%. The flu shot VE varied substantially by virus type and age group.

The U.S. CDC published data regarding the effectiveness of flu vaccines during the 2009-2023 flu seasons. Numerous studies show that influenza vaccination reduces the odds of intensive care unit admission and reduces hospital admissions. Additionally, a recent study's finding reinforces the benefit of flu shots in reducing illnesses even when circulating influenza viruses have drifted.

In a posthoc analysis published on January 27, 2024, study participants receiving QIV-HD were associated with lower incidence rates of hospitalizations for pneumonia or influenza (10 vs. 33 events, IRR 0.30 [95% CI 0.14-0.64], p=0.002) and all-cause hospitalizations (647 vs. 742 events, IRR 0.87 [95% CI 0.76-0.99], p=0.032) compared with QIV-SD. 

Original Research published on December 19, 2023, should real-world evidence (RWE) evaluating clinical outcomes among seniors ≥65 years have shown a superior clinical benefit of aII adjuvanted quadrivalent vaccines over standard egg-derived quadrivalent inactivated influenza vaccines (IIV4e). In a meta-analysis of RWE from cohort design studies, the pooled estimate for the relative vaccine effectiveness (rVE) of aIIV3 compared with IIV4e for the prevention of influenza-related medical encounters was 13.7% (95% confidence interval: 3.1%–24.2%).

An Original Article published by the New England Journal of Medicine on December 14, 2023, confirmed quadrivalent recombinant influenza vaccines contain three times the amount of hemagglutinin protein as standard-dose egg-based vaccines, and the recombinant formulation is not susceptible to antigenic drift during manufacturing. In December 2023, observational data from more than 1.6 million people in the U.S. suggested a high-dose vaccine may also be more effective than standard-dose vaccines for adults aged 50 to 64. A recent clinical study reported that high-dose recombinant vaccines conferred more protection against PCR-confirmed influenza than an egg-based standard-dose vaccine among adults between 50 and 64 years old.

The Journal of Infectious Diseases published results on December 2, 2023, from a test-negative design study evaluating influenza vaccine effectiveness (VE) during the 2022-2023 season. This study concluded VE against influenza-A-associated hospitalizations was 35% (95%CI: 27-43%) overall and 23% and 41% among adults aged 18-64 and ≥65 years, respectively. On November 16, 2023, a significant article published by Clinical Infectious Diseases concluded that during the 2022–2023 influenza season, vaccination reduced the risk of influenza-associated emergency department or urgent care encounters and hospitalizations by 40–48%. An analysis announced on September 19, 2023, found that QIVc showed a clinical benefit compared to QIVe in the prevention of test-confirmed influenza in the outpatient care setting, with an estimated relative vaccine effectiveness (rVEs) (95% CI) of 14.8% (7 – 22) in 2017–-18, 12.5% (4.7 – 19.6) in 2018-–19 and 10% (2.7 – 16.7) in 2019–-20.

On September 8, 2023, the CDC published a report: Interim Effectiveness Estimates of 2023 Southern Hemisphere Influenza Vaccines. The adjusted vaccine effectiveness against severe acute respiratory infection hospitalization associated with any influenza virus during the 2023 Southern Hemisphere flu season was 51.9% (95% Confidence Interval 39.2%–62.0%). During the U.S. CDC meeting on October 20, 2022, the committee reviewed the Comparison of Influenza Vaccine Effectiveness against outpatient and inpatient illness in the 2021–22 season, provided low to non-significant protection (36%) against predominant influenza A/H3N2 illness of varying severity slide #18. Previously, Lisa Grohskopf, with the CDC's Influenza Division, presented highlights regarding the current flu season during the ACIP meeting on June 22, 2022. Preliminary results for the 2021–22 flu season indicate influenza vaccination reduced acute respiratory illness due to influenza A(H3N2) virus by 35% (95% CI: 19‒47) based on data through April 30, 2022.

In Europe, interim vaccine effectiveness estimations for the 2022−2023 season have been reported by the European CDC Vaccine Effectiveness, Burden and Impact Studies multi-country network, with data collected from 16 European countries from October 2022 to January 2023. These interim results indicate a  ≥27% and a ≥50% reduction in disease occurrence among all-age influenza vaccine recipients for influenza A and B, respectively, during the 2022−2023 influenza season.

Influenza Vaccine China

AdimFlu-S (QIS) is a quadrivalent split inactivated vaccine containing hemagglutinin from four influenza virus strains (A and B). The China National Medical Products Administration approved Clover Biopharmaceuticals, Ltd.'s AdimFlu-S in January 2022 for individuals three years older. As of September 2023, AdimFlu-S has been listed in 26 provinces and municipalities in China. The Biologic License Application submission to the Brazilian Health Regulatory Agency (ANVISA) was completed for AdimFlu-S on November 6, 2023. After approval, Clover will work with its local partner to commercialize the product in Brazil. 

SINOVAC's influenza vaccines expanded international market accessibility in the first half of 2023 by gaining more overseas market approvals, such as Pakistan and Chile. On August 31, 2023, a study found that the trivalent influenza vaccine was moderately effective, highly immunogenic, and generally safe for healthy male military service members.

Influenza Vaccine United Kingdom

In the United Kingdom, the NHS published in August 2023 a summary of flu vaccine recommendations for the 2023-2024 influenza season. The U.K.'s NHS says nasal spray vaccine offers the best protection for children and will be available for most persons in 2023.

Influenza and Pneumococcal Vaccine Coadministration

The U.S. CDC recommends administering a pneumococcal vaccine with influenza vaccination during the same visit. Administer each vaccine with a separate syringe and, if feasible, at a different injection site.

Influenza and RSV Vaccine Coadministration

On November 22, 2023, the primary study objectives of a phase 3 clinical trial were met, demonstrating the noninferiority of RSVpreF and SIIV immune responses when RSVpreF vaccine was coadministered with SIIV and that RSVpreF had an acceptable safety and tolerability profile when coadministered with SIIV. The results of this study support the coadministration of RSVpreF and SIIV in an older adult population.

Influenza, RSV, COVID-19 Vaccine Coadministration

In an Original Investigation study published by The JAMA Open Network on September 8, 2023, both reactogenicity and immunogenicity were unchanged primarily in older adults with coadministration of the COVID-19 and season influenza vaccines compared with the administration of COVID-19 vaccination alone. Compared with COVID-19 vaccination alone, the risk of systemic symptoms was similar in the coadministration group (odds ratio, 0.82; 95% CI, 0.43-1.56). Geometric mean titers in the coadministration group were estimated to be 0.84 (95% CI, 0.69-1.04) times lower than in the COVID-19 vaccine–alone group. 

On September 22, 2023, Sarah Schillie, MD, MPH, MBA CAPT, U.S. PublicU.S.lth Service, presented to the CDC's ACIP a draft Addendum to the 2023 Immunization Schedules for Children/Adolescents/Adults, which included COVID-19, RSV, and Influenza coadministration updates. The U.S. CDC on July 21, 2023, that the coadministration of RSV vaccines with other adult vaccines (flu shot) during the same visit is acceptable, and the evidence is mixed regarding increased reactogenicity. And RSV and influenza antibody titers were somewhat lower with coadministration. On June 21, 2023, Pfizer's Alejandra Gurtman, MD, FIDSA, presented to the ACIP, as did Leonard Friedland, M.D. V.P., M.DenV.P.c Affairs and Public Health, GSK, data on RSV and influenza vaccine coadministration. A separate presentation confirmed there is currently limited data available on the immunogenicity of coadministration of RSV vaccines and other vaccines. With coadministration, RSV and influenza antibody titers were generally somewhat lower (slide #9).

Influenza and COVID-19 Combination Vaccine Candidates

Novavax COVID-Influenza Combination (CIC) vaccine candidate uses the full-length, stabilized recombinant spike (rS) protein of the SARS-CoV-2 coronavirus and four wild-type recombinant Hemagglutinin (rHA) proteins from the influenza virus, as antigens. The antigens are organized into distinct nanoparticle complexes recognized by the immune system, working in concert with the Company's Matrix-M™ adjuvant. Recently, anti-S IgG and neutralization responses achieved levels seen in the Phase 3 trial with Novavax's prototype vaccine, with HAI responses generally consistent with Fluad® and Fluzone HD®. Novavax expects to initiate a pivotal Phase 3 trial for the CIC vaccine candidate in the second half of 2024, with the potential for accelerated approval and launch as early as 2026. Novavax, Inc.'s NanoFlu™ is a recombinant hemagglutinin (H.A.) protein nanoparticle influenza vaccine.

Influenza Vaccine Candidates

An updated listing of flu shot candidates is posted at this PVax link.

Flu Shot Price

The U.S. CDC claimed that the Vaccines For Children program is federally funded and provides influenza vaccines and medicines to children at no cost. Internationally, UNICEF offers various price information. According to Fortune Business Insights, the Global Influenza Vaccine Market size is estimated to reach USD 13.58 Billion by 2029, exhibiting a CAGR of 8.8% between 2022 and 2029. And InstantRx™ is a digital gateway empowering people to find flu shot prices easily.

Flu Shots For Children

In the U.S., the annual flu vaccination coverage among children in 2023 was about 47%. The Timing of Influenza Vaccination for Children - Children who require doses should receive their first dose as soon as possible (including during July and August) to allow the second dose (which must be administered ≥4 weeks later to be received, ideally, by the end of October. Children who require only one dose: Vaccination during July and August can be considered for children of any age who need only one influenza vaccine for the season. The WHO reported in October 2023 that 99% of deaths in children under five years of age with influenza-related lower respiratory tract infections are in developing countries. The CDC said on October 10, 2023, that among children and adolescents hospitalized with influenza during the 2022–23 season in hospitals participating in the Influenza Hospitalization Surveillance Network, a lower proportion (18.3%) were vaccinated compared with previous seasons (35.8%–41.8%). The U.S. CDC coU.S.ted a Clinician Outreach and Communication Activity call on August 31, 2023, and presented an Update for Pediatric Providers regarding the 2023-2024 Recommendations for Influenza Prevention and Treatment in Children.

Flu Shots For Pregnant Women

In the U.S., flu vaccination coverage among pregnant women in 2023 was about 36%. At the U.S. CDC U.S.S.e committee meeting on October 25, 2023, Dr. Jamie Loehr (ACIP Work Group Chair) confirmed while there is considerable experience with the safe administration of influenza vaccines in pregnancy, there is less data specific to newer (cell-based) influenza vaccine formulations. On October 26, 2023, Samantha M. Olson, MPH NVSN Flu Lead/ Epidemiologist, presented: Effectiveness of Maternal Influenza Vaccination during Pregnancy against Influenza-associated Hospitalizations & E.D. VisitsE.D.Infants <6 Months of Age. Maternal vaccinations with flu shots have decreased about 10% over the past few years.

During the 2022-2023 flu season, vaccination coverage (about 48%) was similar to that of 2021-2022. Influenza vaccines may be given during any trimester of pregnancy. Geeta Swamy, MD ACIP, presented on October 20, 2022, a clinical trial to compare the safety of Recombinant Influenza Vaccine versus Quadrivalent Inactivated Influenza Vaccine in Pregnancy (NCT03969641).

Flu Shots For Seniors

In the U.S., the oU.U.S. flu vaccination coverage among people 65 years of age and above was about 70% in 2023. On September 19, 2023, the CDC reported that influenza vaccines are often less effective for older adults than younger populations. Sinead Morris, Ph.D., recently presented to the CDC's ACIP, Recommending that enhanced seasonal influenza vaccines in adults aged 65 and older could have wide-ranging impacts on the influenza burden. Lisa Grohskopf, Influenza Division, CDC, presented Influenza Vaccines for Older Adults: GRADE Summary. The JAMA Network reported on August 9, 2022, that adults aged 65 should receive high-dose or adjuvanted seasonal influenza vaccines.

Flu Shots and Alzheimer's Disease and Dementia

The journal BMC Public Health published results from an extensive study in the U.K. that concluded influenza vaccinations were associated with diminished risk of dementia (adjusted HR 0.96 with 95% CI: 0.94–0.97). The Journal of Alzheimer's Disease published a Research Article on June 13, 2022, by UTHealth Houston researchers - Risk of Alzheimer's Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching. People who received at least one influenza vaccine were 40% less likely than their non-vaccinated peers to develop Alzheimer's disease over four years. - The R.R. was 0.R.R.R.% CI, 0.59–0.61), and the ARR was 0.034 (95% CI, 0.033–0.035), corresponding to a number needed to treat 29.4. Conclusion: 

Flu Shots and Asthma

The AAP journal Pediatrics published on March 28, 2022, Safety of Live Attenuated Influenza Vaccine in Children With Conclusion: LAIV4 was not associated with an increased frequency of asthma exacerbations, an increase in asthma-related symptoms, or a decrease in peak expiratory flow rate compared with IIV4 among children aged 5 to 17 years with asthma. 

Flu Shots and Diabetes

The CDC says flu vaccination is essential for people with diabetes because they are at higher risk of developing severe flu complications. About 34% of adults hospitalized with the seasonal flu reported to the CDC had diabetes in recent seasons.

Flu Shots and Pneumonia

Pneumonia can often be prevented following vaccination. As of December 29, 2022, the CDC confirmed among the 2,117 deaths reported last week, 968 listed pneumonia as an underlying or contributing cause of death on the death certificate, 866 had COVID-19, and 283 listed influenza. While current mortality is due primarily to pneumonia and COVID-19, the proportion due to flu is increasing. In a meta-analysis, influenza vaccination significantly reduces pneumonia- and influenza-related hospitalizations. On May 31, 2022, a peer-reviewed Original Investigation published by The JAMA Network found that 'Patients with pneumonia admitted to hospitals with high all-cause readmission rates were more likely to develop adverse events during the index hospitalization.'

Flu Shots and Cardiovascular Disease

A meta-analysis published on November 19, 2023, by the journal Nature - Scientific Reports - highlights the potential of influenza vaccination as an adjunctive strategy in cardiovascular disease prevention. Patients who received the influenza vaccine experienced a risk reduction of over 20% in cardiovascular death. The Lancet Global Health published a study: Influenza vaccine to reduce adverse vascular events in patients with heart failure: a multinational, randomized, double-blind, placebo-controlled trial - Major cardiovascular events are an essential contributor to influenza-associated morbidity and mortality - suggests that there is likely a clinical benefit of giving influenza vaccine, given the apparent reduction in pneumonia, a moderate reduction in hospitalizations, and a reduction in cardiovascular events and deaths during periods of peak circulation of influenza. In a study published by the JAMA Network in April 2022, influenza vaccination was associated with a 34% lower risk of major adverse cardiovascular events, and individuals with recent adverse cardiovascular events had a 45% lower risk.

Flu Shot Immune Imprinting

The concept of "immune imprinting" originated with investigating immune responses to infection by divergent strains of influenza viruses. Scientists found that people had more robust neutralizing antibody responses toward influenza strains that they had been exposed to during childhood. Mechanistically, when different strains of a pathogen infect the host cell, the immune system dedicates most of the response toward recalling the immune effectors used for the original exposure instead of generating reactions against the new strains, thus resulting in immune evasion. 

Avian Influenza (Bird Flu) Vaccines

The U.S. government approved a vaccine for one type of avian influenza (bird flu) virus that protects people from infection and severe disease. However, the CDC says the annual flu offers unknown protection against avian influenza. Zoonotic Influenza (Bird Flu) outbreaks (humans, mammals, and avian)  news for 2023 is posted at this link.

Pandemic Influenza Vaccines

The U.K. HealthU.Kcurity Agency (UKHSA) agreed to an advance purchase agreement with CSL Seqirus in September 2023 to produce over 100 million influenza pandemic vaccines if or when they are needed. Pandemic influenza is not the same as seasonal influenza or avian influenza. An influenza pandemic happens when a new (novel) influenza A virus emerges that can infect people easily and spread from person to person in an efficient and sustained way, and to which most of the world's population does not have immunity. The last flu pandemic occurred in 2009 when a novel influenza A (H1N1) virus emerged. Seasonal influenza circulates yearly and causes thousands of deaths, though it generally causes milder illness among healthy adults because of existing immunity. Avian influenza, meanwhile, cannot be passed from human to human, says the CDC.

Influenza Season 2024

As of 2024, flu season trends are published by Precision Vaccinations.

Clinical Trials

No clinical trials found