ATrain Education


Continuing Education for Health Professionals

Influenza 2018–2019

Module 11

Makeup of the 2018-2019 Influenza Vaccines

Each year, experts from CDC, World Health Organization (WHO), and other institutions study virus samples collected from around the world to identify the influenza viruses that are the most likely to cause illness during the upcoming flu season. This information is used to create a vaccine.

Because flu viruses are constantly changing, it is not possible to predict with certainty which types of viruses will predominate during a given season. Flu viruses can change from one season to the next and can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. Because of these factors, there is always the possibility of a less-than-optimal match between circulating viruses and the viruses in the vaccine.

The 2018–2019 U.S. trivalent influenza vaccines contains the following:

  • an A/Michigan/45/2015 (H1N1)pdm09–like virus,
  • an A/Singapore/INFIMH-16-0019/2016 (H3N2)–like virus, and
  • a B/Colorado/06/2017–like virus (Victoria lineage). (Grohskopf et al., 2018)

The 2018–2-19 U.S. quadrivalent vaccines contain the same three antigens listed above and an additional influenza B virus component, a B/Phuket/3073/2013–like virus (Yamagata lineage). Compared with the 2017–18 season, the composition for 2018–2019 represents changes in the A(H3N2) and B (Victoria) components of both the trivalent and quadrivalent vaccines (Grohskopf et al., 2018).

For the 2018–2019 season, routine annual influenza vaccination of all people aged ≥6 months without contraindications continues to be recommended. A licensed, recommended, and age-appropriate vaccine should be used. (Grohskopf et al., 2018).

Recommendations for the use of LAIV4 (FluMist Quadrivalent) have been updated. Following the previous two seasons, during which ACIP recommended that LAIV4 not be used, for the 2018–2019 season, vaccination providers may choose to administer any licensed, age-appropriate influenza vaccine (IIV, RIV4, or LAIV4). LAIV4 is an option for those for whom it is appropriate (Grohskopf et al., 2018).

Persons with a history of egg allergy of any severity may receive any licensed, recommended, and age-appropriate influenza vaccine (IIV, RIV4, or LAIV4) (Grohskopf et al., 2018).

Recent licensures and labeling changes include expansion of the age indication for Afluria Quadrivalent (IIV4) from ≥18 years to ≥5 years and expansion of the age indication for Fluarix Quadrivalent (IIV4), previously licensed for ≥3 years, to ≥6 months (Grohskopf et al., 2018).

Balancing considerations regarding the unpredictability of timing of onset of the influenza season and concerns that vaccine-induced immunity might wane over the course of a season, it is recommended that vaccination should be offered by the end of October. Children aged 6 months through 8 years who require 2 doses should receive their first dose as soon as possible after vaccine becomes available, to allow the second dose (which must be administered ≥4 weeks later) to be received by the end of October (Grohskopf et al., 2018).

Community vaccination programs should balance maximizing likelihood of persistence of vaccine-induced protection through the season with avoiding missed opportunities to vaccinate or vaccinating after onset of influenza circulation occurs. Revaccination later in the season of persons who have already been fully vaccinated is not recommended (Grohskopf et al., 2018).

For a table of approved influenza vaccines for the 2018-2019 season, please see:


Giving an Influenza Vaccination via Needle

photo: vaccination

Source: United States Navy. Public domain.

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