The World Health Organization (WHO) has recommended that quadrivalent vaccines for the 2018-2019 northern hemisphere influenza season contain the following:

• an A/Michigan/45/2015 (H1N1) pdm09-like virus;
• an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus;
• a B/Colorado/06/2017-like virus (B/Victoria/2/87 lineage); and
• a B/Phuket/3073/2013-like virus (B/Yamagata/16/88 lineage).

The WHO recommended that the influenza B virus component of trivalent vaccines for the 2018-2019 northern hemisphere influenza season be:

• a B/Colorado/06/2017-like virus of the B/Victoria/2/87-lineage.

How is this different from last year’s recommendation?

•A/Singapore/INFIMH-16-0019/2016-like virus replaced the A/Hong Kong/4801/2014-like virus.

•B/Colorado/06/2017-like virus [B/Victoria/2/87 lineage] replaced the B/Brisbane/60/2008-like virus   [B/Victoria/2/87 lineage].

How were these recommendations determined?

Every year, industry professionals survey the influenza viruses that are presently circulating. Based on the data they collect, they forecast which of those viruses are most likely to disseminate during the approaching flu season. The vaccine virus and the influenza virus predicted to most commonly circulate must be similar for the vaccine to combat the virus. The similarities between a vaccine virus and the virus itself are determined through a series of tests, including antigenic characterization or genetic characterization. These tests indicate if the vaccine can yield an immune response against the flu virus in people. They also want to ensure that the virus used in the production of vaccines will be suitable to protect against the viruses they expect to circulate in the impending season. It is imperative that they have enough time to properly isolate and grow the virus as well as test it. This process is crucial to the timeline of production for the large quantity of vaccine virus necessary to make vaccine.