Recent WHO seasonal influenza vaccine composition recommendations:

2020–2021 northern hemisphere
The composition of virus vaccines for use in the 2020–2021 Northern Hemisphere influenza season recommended by the World Health Organization on February 28, 2020, is:for egg-based:

an A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09-like virus
an A/Hong Kong/2671/2019 (H3N2)-like virus
a B/Washington/02/2019 (B/Victoria lineage)-like virus
a B/Phuket/3073/2013 (B/Yamagata lineage)-like virusfor cell- or recombinant-based:
an A/Hawaii/70/2019 (H1N1)pdm09-like virus
an A/Hong Kong/45/2019 (H3N2)-like virus
a B/Washington/02/2019 (B/Victoria lineage)-like virus
a B/Phuket/3073/2013 (B/Yamagata lineage)-like virusThe WHO recommends that trivalent vaccines use as their influenza B virus a B/Washington/02/2019 (B/Victoria lineage)-like virus. United StatesThe Vaccines and Related Biological Products Advisory Committee (VRBPAC) of the Food and Drug Administration (FDA) recommended that the quadrivalent formulation of egg-based influenza vaccines for the US 2020–2021 influenza season contain the following:
an A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09-like virus;
an A/HongKong/2671/2019 (H3N2)-like virus;
a B/Washington/02/2019-like virus (B/Victoria lineage);
a B/Phuket/3073/2013-like virus (B/Yamagata lineage).The committee recommended that the quadrivalent formulation of cell- or recombinant-based influenza vaccines for the US 2020–2021 influenza season contain the following:
an A/Hawaii/70/2019 (H1N1)pdm09-like virus;
an A/HongKong/45/2019 (H3N2)-like virus;
a B/Washington/02/2019-like virus (B/Victoria lineage);
a B/Phuket/3073/2013-like virus (B/Yamagata lineage)For trivalent influenza vaccines for use in the US for the 2020–2021 influenza season, depending on the manufacturing method of the vaccine, the committee recommended that the A(H1N1)pdm09, A(H3N2) and B/Victoria lineage viruses recommended above for the quadrivalent vaccines be used.
Most swine flu vaccines include an H1N1 and an H3N2 strain. Swine influenza has been recognized as a major problem since the outbreak in 1976. Evolution of the virus has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the problem when the virus strains match enough to have significant cross-protection. Customised (autogenous) vaccines made from the specific viruses isolated, are made and used in the more difficult cases. The vaccine manufacturer Novartis claims that the H3N2 strain (first identified in 1998) has brought major losses to pig farmers. Abortion storms are a common sign and sows stop eating for a few days and run a high fever. The mortality rate can be as high as fifteen percent. Dogs
In 2004, influenza A virus subtype H3N8 was discovered to cause canine influenza. Because of the lack of previous exposure to this virus, dogs have no natural immunity to this virus. However, a vaccine was found in 2004. Annual reformulation
Each year, three strains are chosen for selection in that years flu vaccination by the WHO Global Influenza Surveillance and Response System. The chosen strains are the H1N1, H3N2, and Type-B strains thought most likely to cause significant human suffering in the coming season. Starting with the 2012–2013 Northern Hemisphere influenza season (coincident with the approval of quadrivalent influenza vaccines), the WHO has also recommended a 2nd B-strain for use in quadrivalent vaccines.