The World Health Organization released recommended composition of influenza virus vaccines for the upcoming 2021-22 flu season.1 Because of the response to the COVID-19 pandemic, public reporting of the 2019-20 flu season was limited. However, efforts to curtail the spread of COVID-19 including restrictions on travel, use of respiratory protection, and social-distancing measures contributed to record-low levels of influenza detections were reported and fewer viruses were available for characterization during the September 2020 to January 2021 time-period than in previous years, said the WHO.
Between September 2020 and January 2021, the percent positivity for influenza viruses globally was less than 0.2%. In contrast, the average percent positivity during the same reporting period of the 3 previous influenza seasons (2017-2020) was 17%.
In North America, “the percentage of tests that were positive for influenza virus was very low, despite testing at usual or increased levels,” according to WHO. “The majority of detections were influenza B, and where subtyping was performed, both A(H1N1)pdm09 and A(H3N2) viruses were reported.”
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The WHO recommends that quadrivalent vaccines for use in the 2021-22 northern hemisphere influenza season contain the following:
Egg-based vaccines
- A/Victoria/2570/2019 (H1N1)pdm09-like virus;
- A/Cambodia/e0826360/2020 (H3N2)-like virus; and
- B/Washington/02/2019 (B/Victoria lineage)-like virus.
Cell- or recombinant-based vaccines
- A/Wisconsin/588/2019 (H1N1)pdm09-like virus;
- A/Cambodia/e0826360/2020 (H3N2)-like virus; and
- B/Washington/02/2019 (B/Victoria lineage)-like virus; and
- B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
The WHO also recommends that trivalent influenza vaccines for use in the 2021-22 northern hemisphere influenza season contain the following:
Egg-based vaccines
- A/Victoria/2570/2019 (H1N1)pdm09-like virus;
- A/Cambodia/e0826360/2020 (H3N2)-like virus; and
- B/Washington/02/2019 (B/Victoria lineage)-like virus.
Cell- or recombinant-based vaccines
- A/Wisconsin/588/2019 (H1N1)pdm09-like virus;
- A/Cambodia/e0826360/2020 (H3N2)-like virus; and
- B/Washington/02/2019 (B/Victoria lineage)-like virus.
Reference
World Health Organization. Recommended composition of influenza virus vaccines for use in the 2021 – 2022 northern hemisphere influenza season. February 26, 2021. Accessed April 20, 2021. https://www.who.int/influenza/vaccines/virus/recommendations/2021-22_north/en/.
