Vaccine Info

Influenza Vaccines

Last Reviewed
November 18, 2020

Influenza vaccines, known as flu shots, protect people against the influenza viruses that research indicates will be most common during the upcoming season. 

Most importantly, influenza vaccines do not cause the seasonal flu since they are made with either killed or weakened viruses, says the U.S. CDC.

Flu viruses are classified by proteins on the outer surface of the virus: hemagglutinin (H) and neuraminidase (N). There are 18 different H subtypes and 11 different N subtypes, and viruses can be further broken down into different strains within those subtypes. As an example, there are various strains of the H1N1 influenza virus. The H protein (also called HA) enables the flu virus to enter a human cell. It is made up of a head and a stem.

Seasonal flu vaccines fight infection by inducing antibodies that target the HA head. This region varies season to season, which is why flu vaccines must be updated each year, says the U.S. NIH.

The most common flu shot for the 2020-2021 influenza season in the Northern Hemisphere are quadrivalent vaccines that protect people against 4 viruses; influenza A (H1N1) virus, influenza A (H3N2) virus, and 2 influenza B viruses, said the CDC on August 21, 2020.

Most people over 6 months of age are encouraged to get vaccinated every flu season since influenza infections can create severe consequences. The U.S. CDC’s Advisory Committee on Immunization Practices has made this recommendation since the 2010-11 influenza season.

And the adjusted vaccine effectiveness estimates for influenza seasons from 2004-2018 are found on this CDC webpage.

Two new influenza vaccines have been licensed for use in people aged 65 years and older for the 2020-2021 flu season: a quadrivalent high-dose influenza vaccine and a quadrivalent adjuvanted influenza vaccine. Previously, high-dose and adjuvanted influenza vaccines were only available in trivalent formulations.

Quadrivalent Influenza Vaccines - 2020-2021

6 months and older

  • Afluria is an inactivated quadrivalent influenza vaccine indicated for active immunization against influenza disease caused by influenza virus subtypes A and type B.
  • Fluarix is prepared from influenza viruses propagated in embryonated chicken eggs.
  • Flulaval is a quadrivalent, split-virion, inactivated influenza virus vaccine prepared from virus propagated in the allantoic cavity of embryonated hens’ eggs.
  • Fluzone Quadrivalent is an inactivated vaccine indicated for the prevention of influenza disease caused by influenza A subtype viruses and type B viruses

2-49 years of age

  • FluMist is an Intranasal vaccine that is a live quadrivalent vaccine that is formulated to contain four vaccine virus strains.

4 years of age and older

  • Flucelvax is a cell culture-based flu vaccine to help offer protection against 4 flu virus strains 

18-64 years of age

  • Flublok made without the use of eggs and therefore is not subject to the mutations that are sometimes introduced into the vaccine during the process of egg adaptation that can cause the traditional vaccines to be ineffective.

65 years and older

  • Fluad consists of an inactivated, quadrivalent influenza virus antigen produced in eggs and an oil-in-water emulsion adjuvant, MF59C.1.
  • Fluzone High-Dose contains 4 times the antigen of standard-dose inactivated influenza vaccines.

Trivalent Influenza Vaccine - 2020-2021

65 years and older

  • Fluad consists of an inactivated, trivalent influenza virus antigen produced in eggs and an oil-in-water emulsion adjuvant, MF59C.1.

Influenza Vaccine Candidates

  • Flu-v Influenza Vaccine is a synthetic universal flu vaccine candidate offering long-lasting protection across a broad spectrum of influenza.
  • M-001 influenza vaccine candidate is a recombinant protein containing 9 conserved epitopes from Influenza A and B that are common to the vast majority of influenza viruses.
  • MVA-M1+NP vaccine candidate consists of MVA, a replication-deficient pox viral vector that has been safely tested in thousands of patients, to generate a strong immune reaction against Matrix 1 (M1) and Nucleoprotein (NP) influenza antigens. 
  • NasoVAX is a recombinant intranasal vaccine that is being developed for both seasonal and pandemic use
  • Redeeflu is a nasal vaccine candidate utilizing a proprietary M2 deleted, single replication influenza virus.

Influenza Vaccine News

November 23, 2020 - The WHO GISRS laboratories tested more than 1,086,381 specimens during that time period. A total of 100 specimens were positive for influenza viruses, of which 63 (63%) were typed as influenza A and 37 (37%) as influenza B. Of the sub-typed influenza A viruses, 7 (11.3%) were influenza A(H1N1)pdm09 and 55 (88.7%) were influenza A(H3N2). Of the characterized B viruses, 1 (6.7%) belonged to the B-Yamagata lineage and 14 (93.3%) to the B-Victoria lineage.

November 20, 2020 - Key Updates for Week #46, ending November 14, 2020, published by the U.S. CDC. Nationwide during week #46, 1.5% of patient visits reported through ILINet were due to ILI. This percentage is below the national baseline of 2.6%.

November 9, 2020 - The WHO Report #380 indicated a total of 140 specimens were positive for influenza viruses, of which 80 (57.1%) were typed as influenza A and 60 (42.9%) as influenza B. Of the sub-typed influenza A viruses, 2 (5.4%) were influenza A(H1N1)pdm09 and 35 (94.6%) were influenza A(H3N2). Of the characterized B viruses, 1 (6.7%) belonged to the B-Yamagata lineage and 14 (93.3%) to the B-Victoria lineage.

November 6, 2020 - In the USA during week #44, 1.3% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI). This percentage is below the national baseline of 2.6%, reported the U.S. CDC. And, based on mortality surveillance data available on November 5, 2020, 8.1% of the deaths occurring during the week ending October 31, 2020, were due to pneumonia, influenza, and COVID-19 (PIC). This PIC percentage is above the epidemic threshold of 6.0% for week #44.

October 29, 2020 - Women had a 0·7–0·9% risk of influenza per month of pregnancy during the influenza season, and antenatal influenza was associated with increased risk for some adverse pregnancy outcomes. These findings support the added value of antenatal influenza vaccination to improve perinatal outcomes.

October 28, 2020 - Kaiser Permanente dentists near Portland, Oregon will soon begin a pilot program where patients over the age of 12 can receive an annual flu shot during their dental appointment. Oregon dentists are authorized to administer vaccines based on the passage of House Bill 2220.

October 26, 2020 - National Influenza Centres and other national influenza laboratories from 69 countries, areas or territories reported data to FluNet for the time period from 28 September 2020 to 11 October 2020.

October 26, 2020 - South Korean authorities have said they found no direct link between the deaths and the vaccines against flu, which kills at least 3,000 South Koreans each year. “Do trust the health authorities’ conclusion...reached after a review with experts,” President Moon Jae-in said. “There is a need to expand the influenza vaccination this year not only to prevent the flu but also to ward off concurrent infection and spread of flu and COVID-19."

October 21, 2020 - Seqirus announced evidence indicating that an MF59®-adjuvanted trivalent seasonal influenza vaccine was more effective than standard, non-adjuvanted quadrivalent influenza vaccines in reducing influenza-related medical encounters in adults 65 years and older with at least one underlying health condition.

October 21, 2020 - Vir Biotechnology announced the presentation of preclinical and Phase 1 data demonstrating the broad neutralizing ability, high-level effector function, extended half-life, and tolerability of the VIR-2482 vaccine candidate in the prevention of influenza A, will be presented at IDWeek 2020.

October 16, 2020 - The U.S. CDC confirmed during week #41 that only 1.2% of patient visits in the USA reported through the U.S. Outpatient Influenza-like Illness Surveillance Network were due to influenza-like illness.

October 13, 2020 - Study published by The Lancet: Efficacy, immunogenicity, and safety of a plant-derived, quadrivalent, virus-like particle influenza vaccine in adults (18–64 years) and older adults (≥65 years): two multicentre, randomized phase 3 trials. These efficacy studies are the first large-scale studies of any plant-derived human vaccine. Together, they show that the plant-derived QVLP vaccine can provide substantial protection against respiratory illness and influenza-like illness caused by influenza viruses in adults. QVLP vaccine was well tolerated and no major safety signal arose in participants who received the QVLP vaccine across the two studies.

October 8, 2020 - A new study identified that seasonality of cardiovascular events may be associated with seasonality in Influenza‐Like‐Illness, though VE did not modify this relationship.

October 8, 2020 - Walgreens survey: Nearly three-fourths of U.S. adults plan on getting a flu shot this season, but a survey suggests misconceptions could keep the other fourth from getting vaccinated.

October 7, 2020 - Universal flu shot study published in Cell: Defining and Manipulating B Cell Immunodominance Hierarchies to Elicit Broadly Neutralizing Antibody Responses against Influenza Virus.

October 6, 2020 - The Massachusetts Department of Public Health (DPH) announced it has revised the influenza vaccination requirements for staff at nursing homes, rest homes, assisted living residences, adult day health programs, and out-of-hospital dialysis units. The DPH order eliminates the option for staff to opt-out of getting a flu vaccine, with exemptions only for medical or religious reasons.

October 5, 2020 - A study found the 2018–2019 influenza vaccine reduced pediatric influenza A-associated hospitalizations and ED visits by 40% to 60%, despite the circulation of a drifted A(H3N2) clade.

October 5, 2020 - The ECDC published a systematic review of flu vaccine effectiveness studies. The evidence base for the efficacy and effectiveness of newer and enhanced influenza vaccines is limited at present. Based on reviewed evidence, it is probable that these vaccines provide greater protection than no vaccination.

October 2, 2020 - CDC data aggregated during Week #39 found just 1.0% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network were due to influenza-like illness, which is well below the national baseline of 2.4%.

October 2, 2020 - Based on death certificate data, the U.S. CDC reported the percentage of deaths attributed to pneumonia, influenza, or COVID-19 for week #39 is 6.4%. This is currently lower than the percentage during week 38 (9.5%).

October 1, 2020 - The American Academy of PediatricsPolicy Statement: Recommendations for Prevention and Control of Influenza in Children, 2020–2021.

October 1, 2020 - National Survey: Attitudes about Influenza, Pneumococcal Disease, and COVID-19.

September 25, 2020 - The World Health Organization (WHO) influenza vaccine advisors announced the strains to include in vaccines for the Southern Hemisphere's 2021 season. When compared with the current season's vaccines, the group's recommendation swaps out both the 2009 H1N1 strains and the H3N2 influenza strains for egg-based vaccines, switching from the A/South Australia/34/2019-like virus to an A/Hong Kong/2671/2019-like virus.

September 25, 2020 - US CDC Weekly U.S. Influenza Surveillance Report: 2019-2020 Influenza Season Week 38, ending September 19, 2020.

September 23, 2020 - China's first domestically made live attenuated nasal spray flu vaccine was used for the first time in Xi'an, Shaanxi province, reported China's National Medical Products Administration.

September 21, 2020 - WHO SAGE Seasonal Influenza Vaccination Recommendations during the COVID-19 Pandemic.

September 18, 2020 - The CDC's 2019-2020 Influenza Season Week #37, with data ending on September 12, 2020. Following the widespread adoption of community mitigation measures to reduce transmission of SARS-CoV-2, the virus that causes COVID-19, the percentage of U.S. respiratory specimens submitted for influenza testing that tested positive decreased from >20% to 2.3% and has remained at historically low interseasonal levels (0.2% versus 1–2%). Data from Southern Hemisphere countries also indicate little influenza activity, said the CDC.

September 16, 2020 - The publication of real-world evidence (RWE) on the company's cell-based quadrivalent influenza vaccine (QIVc) in the peer-reviewed medical journal Vaccine. This study's results indicate QIVc was more effective compared with standard, egg-based quadrivalent vaccine in preventing influenza-related hospitalizations/ER visits, all-cause hospitalizations, and hospitalizations/ER visits related to serious respiratory events.

September 11, 2020 - Scott Hensley, Ph.D., an associate professor of Microbiology at the Perelman School of Medicine in Pennsylvania, it is possible that the presence of high levels of non-neutralizing antibodies in middle-aged adults has contributed to the continued persistence of H3N2 viruses in the human population.

September 11, 2020 - The U.S. CDC 2019-2020 Influenza Season Week #36, ending September 5, 2020.

September 8, 2020 - The American Academy of Pediatrics in its policy statement, “Recommendations for Prevention and Control of Influenza in Children, 2020–2021,” offers the option of a flu shot or nasal spray flu vaccine this season.

September 2, 2020 - The Janssen Pharmaceutical Companies announced that it has made a strategic decision to discontinue the development of pimodivir, an investigational antiviral treatment for influenza A infection.

September 1, 2020 - A large cohort study published by the Annals of Internal Medicine found no association between maternal influenza A(H1N1)pdm09 vaccination during pregnancy and risk for autism spectrum disorder in the offspring.

August 31, 2020 - ​The WHO published update number 375, based on data up to August 16, 2020.

August 31, 2020 - Researchers have developed an approach to assess whether a vaccine activates the kind of immune cells needed for long-lasting immunity against new influenza strains. These results indicate that influenza virus vaccination of humans can elicit a GC reaction to which B cell clones targeting novel epitopes are more likely to be recruited, thereby broadening the spectrum of vaccine-induced protective antibodies against this rapidly mutating pathogen.

August 31, 2020 - Flu Vaccine Linked to Reduced CV Mortality in Adults With Diabetes. Although both diabetes and influenza are associated with increased risk of AMI and stroke, few studies have explored the relationship between influenza vaccinations and cardiovascular outcomes in individuals with diabetes, the authors wrote.

August 28, 2020 - U.S. CDC published Week #34 influenza report.

August 25, 2020 - A Cross-sectional Study: Acute Cardiovascular Events Associated With Influenza in Hospitalized Adults. In this population-based study of adults hospitalized with influenza, almost 12% of patients had an acute cardiovascular event.

August 25, 2020 - PAHO's Regional Update, Influenza. Epidemiological Week #33.

August 20, 2020 - U.S. CDC report: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — the United States, 2020–21 Influenza Season.

August 19, 2020 - Massachusetts State public health officials announced that influenza immunization will be required for all children 6 months of age or older who are attending Massachusetts child care, pre-school, kindergarten, K-12, and colleges and universities during 2021.

August 18, 2020 - A city-wide flu shot intervention was associated with increased influenza vaccination coverage, decreased illness-specific school absences among students, and lower influenza transmission community-wide, suggesting that the intervention may have produced herd effects.

August 17, 2020 - The WHO reported the Southern Hemisphere's flu season runs from May through October each year, but the season hasn't started yet. Sporadic influenza outbreaks have been detected in the Caribbean, Central America, and tropical parts of South America and Africa.

Of about 205,000 flu specimens tested in the last half of July, only 40 were positive for flu, and half were influenza A and half were influenza B. Of the subtyped influenza A viruses, 75% were H3N2.

August 14, 2020 - A new study published in JAMA concluded saying 'Despite the rapid pace of progress in the areas of SARS-CoV-2 diagnostics, treatment, and vaccine development, the population remains vulnerable to concurrent influenza and COVID-19 epidemics.'

August 13, 2020 - The first shipment of FLUMIST® QUADRIVALENT doses in the USA for the Northern Hemisphere's 2020-2021 influenza season. In response to the SARS-CoV-2 pandemic, AstraZeneca has increased production of FluMist doses by over 25% more than previously planned, a majority of which are expected to be available by the end of September 2020.

August 10, 2020 - The Alzheimer’s Association indicates these are possible connections between influenza and pneumonia vaccinations with reducing or delaying cognitive decline. Both studies were previewed at AAIC prior to peer-reviewed journal publication.

August 9, 2020 - During 2020, the majority of reported laboratory-confirmed influenza cases in Australia were influenza A (87.3%).

August 9, 2020 - The University of California announced requirements for flu shots for students, faculty, and staff.

August 7, 2020 - The U.S. CDC reported a total of 187 influenza-associated pediatric fatalities during the 2019-2020 flu season have been reported to CDC.

August 7, 2020 - Researchers at Kanazawa University report in Nano Letters a high-speed atomic force microscopy study on a biological event that occurs when a flu virus enters and infects its host cell. The real-time visualization of influenza A hemagglutinin has enhanced the understanding of the fusogenic transition of HA and its interactions with host endosomes.

August 6, 2020 - A new study concludes that opening clinics dedicated specifically to treating influenza can limit the number of people infected and help to 'flatten the curve,' or reduce the peak prevalence rate. While the work focused on influenza, the findings are relevant for policymakers seeking ways to reduce the impacts of the ongoing COVID-19 pandemic.

August 3, 2020 - The WHO reported influenza activity was reported at lower levels than expected for this time of the year. As an example, in the temperate zones of the Southern Hemisphere, the influenza season has not commenced. And in the temperate zone of the Northern Hemisphere, influenza activity remained at interseasonal levels

July 30, 2020 - Seqirus announced it has begun shipping its portfolio of seasonal influenza vaccines to customers in the U.S. for the 2020/21 influenza season. Seqirus is well-positioned to supply up to 60 million vaccine doses for the U.S. market.

July 28, 2020 - GSK announced it started shipping more than 50 million quadrivalent influenza vaccine doses to US healthcare providers and pharmacies for the 2020-21 flu season. This data indicates a 9% increase from the last flu season.

July 27, 2020 - At the virtual American Heart Association’s Basic Cardiovascular Sciences 2020 Scientific Session, new research found adults age 50+ who did get a flu shot, had better outcomes in the year following vaccination, with a 28% lower risk of heart attack, a 73% lower risk of death, and an 85% lower risk of cardiac arrest.

July 23, 2020 - A study published by the NEJM: Baloxavir Marboxil for Prophylaxis against Influenza in Household Contacts.

July 9, 2020 - An analysis published by the NEJM showed that children 2 to 5 years old with birthdays in September through December were more likely to receive influenza vaccination and less likely to have influenza than those with birthdays earlier in the year before a vaccine is available.

July 9, 2020 - A new study found that among adults obesity is associated with susceptibility to H1N1pdm infection and with symptoms associated with H1N1pdm infection, but not with susceptibility to H3N2 infection or associated symptoms.

July 2, 2020 - the U.S. FDA issued an emergency use authorization for the 3rd diagnostic test for detection and differentiation of the viruses that cause flu and COVID-19 in individuals suspected of COVID-19 disease. The FDA has previously issued authorizations to BioFire Diagnostics LLC and QIAGEN GmbH for their tests, which include many other respiratory organisms in addition to the viruses that cause flu and COVID-19.

February 21, 2020 -  According to the CDC Morbidity and Mortality Weekly Report, the current influenza vaccine has been 45% effective overall against 2019-2020 seasonal influenza A and B viruses.

November 25, 2020 - Study: Forecasting type-specific seasonal influenza after 26 weeks in the United States using influenza activities in other countries. This study forecasts the 2018–2019 seasonal influenza after 26 weeks in the U.S. using the 2018 seasonal influenza in Australia and Chile. The correlation between the seasonal influenza patterns in the U.S., Australia, and Chile could be used to forecast the next seasonal influenza pattern, which can help to determine influenza vaccine strategy approximately six months ahead in the U.S. Our prediction model allows to estimate peak timing, peak intensity, and type-specific influenza activities for next season at 40th week.

Universal Influenza Vaccine Research

A key focus of influenza research programs is developing a universal flu vaccine that provides robust, long-lasting protection against multiple subtypes of flu, rather than a select few. Such a vaccine would eliminate the need to update and administer the seasonal flu vaccine each year and could provide protection against newly emerging flu strains, potentially including those that could cause a flu pandemic.

Influenza Medicines

There are several medications such as Tamiflu or Xofluza (Baloxavir Marboxil) that can lessen the severity and duration of the seasonal flu, but they're most effective in the first 48 hours after you experience influenza symptoms. Access to these medicines requires a healthcare provider's prescription.

    Influenza FAQs

    Note: This page's content is aggregated from the US CDC, the WHO, pharmaceutical manufacturers, university studies, and the Precision Vaccinations news network. This content is reviewed by healthcare professionals, such as Dr. Robert Carlson.