October is the best month to get an influenza shot for full-season protection, as it can take up to 2 weeks for antibodies to develop. However, patients may be reluctant to get immunizations if they’ve heard recent reports that this year’s vaccine is not well matched to the viruses likely to circulate this winter.
There is some cause for concern. In late September, the World Health Organization issued its recommendation for the 2020 Southern Hemisphere vaccine. The four strains included two swaps from the vaccine that will be administered in the United States this fall, based on the strains currently in circulation in Australia and New Zealand.
The U.S. vaccine available now includes components to protect against A/Kansas/14/2017 (H3N2)-like virus, A/Brisbane/02/2018 (H1N1) pdm09-like virus, B/Colorado/06/2017-like virus (Victoria lineage), and B/Phuket/3073/2013-like virus (Yamagata lineage). The trivalent formulations available in the U.S. this year, Fluad and Fluzone High-Dose, will not have the B/Yamagata component.
The WHO’s recommendations for use in the Southern Hemisphere in 2020 replaced the H3N2 component with A/South Australia/34/2019 (H3N2)-like virus and the B/Victoria lineage with B/Washington/02/2019-like virus.
That doesn’t mean the same strains will necessarily feature in the upcoming flu season in the Northern Hemisphere. Influenza viruses are extremely mutable and often drift over the course of a season. Even if the strains currently seen in the Southern Hemisphere do circulate here, they may not be the strains that dominate or cause the most illness.
Pharmacists should stress the benefits of getting a flu vaccine, even if the match proves to be less than perfect. First, there is every indication that two of the components in the quadrivalent formulations will be a match, and vaccination will provide significant protection against those. All regular-dose flu shots and recombinant vaccine will be quadrivalent this season.
In addition, the CDC notes that “antibodies made in response to vaccination with one flu virus sometimes can provide protection against different but related flu viruses. A less than ideal match may result in reduced vaccine effectiveness against the flu virus that is different from what is in the flu vaccine, but it might still provide some protection against flu illness.”
That means the vaccine could still mitigate the most serious complications associated with influenza, reducing the risk of hospitalization and death. CDC studies show that vaccinated patients who were hospitalized with the flu were 37% to 60% less likely to be admitted to intensive care, were 52% to 79% less likely to die, and spent 4 fewer days in the hospital than those who were not vaccinated.
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Published October 30, 2019