Changes in Influenza Vaccine May Improve Coverage


The influenza vaccine for the 2019-2020 flu season will look different than it has for the past few seasons.

The influenza vaccine for the 2019-2020 flu season will look different than it has for the past few seasons. The FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) and the World Health Organization (WHO) have both selected new strains for each of the 2 Influenza A strains included in the trivalent and quadrivalent vaccines.1-2

Trivalent vaccines will include:

  • Influenza A: A/Kansas/14/2017 (H3N2)-like virus
  • Influenza A: A/Brisbane/02/2018 (H1N1)pdm09-like virus
  • Influenza B: B/Colorado/06/2017-like (Victoria lineage) virus

Quadrivalent vaccines will also include a second lineage of the Influenza B virus: B/Phuket/3073/2013-like (Yamagata lineage) virus.1-3

The vaccine selection came after the VRBPAC and the WHO made the uncharacteristic step of delaying the decision on which Influenza A (H3N2) strain to include in the vaccine composition. The 3 other strains in the vaccine were chosen on February 21, 2019 by the WHO and VRBPAC on March 6, 2019. The 2 strains recommended to cover the Victoria and Yamagata lineages of Influenza B remain unchanged. However, experts recommend a new strain for Influenza A (H1N1)pdm09-like virus in February based on data of circulating viruses. The recommendation for the Influenza (H3N2) strain was made by the WHO on March 21, 2019 and chosen for United States vaccines by VRBPAC 1 day later. 1-3

Though postponement of the vaccine composition has occurred before, it is rare. Most influenza vaccines are derived from chicken eggs, which take months to produce. The submission of strain compositions so far in advance is necessary in order to ensure that an appropriate supply of influenza vaccination will be available and distributed by the time flu season begins in the Northern Hemisphere, in October.

The delay is the result of a rise in the proportion of influenza viruses within 1 antigenically distinct group, particularly within the US, Europe, Israel, Asia, and Oceania. The additional time allowed experts more opportunity to monitor circulating influenza viruses and characterization of potential strains to include in the vaccine.1-3 With the majority of circulating influenza strains characterized as Influenza A in recent years, and only about a 44% efficacy rate against these strains, a delay to ensure an increased likelihood of vaccine match for the next flu season seems justified.

It is too soon to determine what impact the postponed recommendations will have on vaccine delivery and availability for the 2019-2020 season. The WHO reports that they feel joint efforts with stakeholders and vaccine manufacturers will minimize any delay of vaccine supply.2 However, they are recommending stakeholders prepare for a 2-4 week potential delay in vaccine availability. Influenza vaccine programs, strategies, education, and other timelines should be adjusted accordingly.

The American Academy of Pediatrics (AAP) also updated their recommendations for the 2019-2020 flu season. In the upcoming season, the AAP recommends that children be vaccinated with any licensed influenza vaccine in accordance with CDC recommendations. This is a change from the past 3 flu seasons where the inactivated injection was recommended over the nasal vaccine and from years prior where a preference for the nasal vaccine was stated. The recommendation for injection influenza vaccines began with the 2016-2017 influenza season based on poor efficacy of the nasal vaccine against Influenza A (H1N1). Since that time, the manufacturer of the nasal vaccine has changed the formulation and preliminary data on the new Influenza A (H1N1) strain is encouraging.5

The influenza vaccine remains the most effective way to prevent the spread of the virus. Preliminary estimates from the CDC indicate that there have been 36.9-42.4 million cases of influenza and 36,500-59,500 influenza-related deaths, so far, in the 2018-2019 season.6

The burden of influenza is down from the 2017-2018 flu season. This may be due in part by an increase in vaccinations by 6.8% in children and 6.4% this year.7

The quest of a better vaccine match to circulating strains may reduce influenza-related complications much more in the next flu season. Even if vaccine supply is delayed, pharmacists and other health care providers should remain diligent in recommendations and reminders to ensure as many people as possible are vaccinated once it is available.


  • Centers for Disease Control and Prevention. Frequently Asked Flu Questions: 2019-2020 Influenza Season. CDC website. Updated March 25, 2019. Accessed May 2, 2019.
  • World Health Organization. Recommended composition of influenza virus vaccines for use in the 2019-2020 northern hemisphere season. WHO website. Updated March 21, 2019. Accessed May 2, 2019.
  • Food and Drug Administration. Summary of the teleconference held on Wednesday, 13 March 2019 for A(H3N2) Composition of Influenza Virus Vaccines for the Northern Hemisphere 2019-2020. FDA website. Updated March 13, 2019. Accessed May 2, 2019.
  • Centers for Disease Control and Prevention. US Flue VE Data for 2018-2019: Interim Estimates MMWR. Updated February 25, 2019. Accessed May 2, 2019.
  • American Academy of Pediatrics. AAP Updates Vaccine Recommendations for the 2019-2020 Flu Season. AAP website. Updated March 14, 2019. Accessed May 2, 2019.
  • Centers for Disease Control and Prevention. 2018-2019 U.S. Flu Season: preliminary Burden Estimates. CDC website. Updated April 25, 2019. Accessed May 2, 2019.
  • Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases. Early-Season Flu Vaccination Coverage- United States, November 2018. CDC website. Updated 14 December 2019. Accessed May 2, 2019.

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