The choice looks simple enough: the familiar 3-strain 'trivalent' influenza vaccine or the new 4-strain quadrivalent version?

The traditional trivalent injectable vaccine (TIV) vaccine should again be effective against the three principal flu strains predicted for 2016 – A(H1N1), A(H3N2), and B/ Brisbane. It's also cheaper at $40.00 per dose at all Sonic HealthPlus clinics (includes consultation and vaccination).

Several trivalent products will be available in Australia from late March, a month earlier than the two imported 4-strain or 'quadrivalent' vaccines. For the first time, a quadrivalent (QIV) vaccine (FluarixTetra) will be the only flu vaccine available to Australians eligible for free vaccination through the government-sponsored National Immunisation Program (NIP). Fluarix Tetra and the privately-available FluQuadri Adult will contain the trio of strains mentioned above, plus B/Phuket.

The quadrivalent vaccines, each selling for $50 per dose is now available at all Sonic HealthPlus clinics (includes consultation and vaccination).

The unpredictability of flu

While quadrivalent flu vaccines are here to stay, it's hard to say just how important the protection that the fourth strain will prove to be.

In most years, B strains account for fewest flu cases than the A strains.

Not last winter: The final national Influenza Surveillance Report¹ published in December described the 2015 flu season as 'characterised by the predominant circulation of influenza B'. B/Yamagata lineage viruses and B/Victoria accounted for 62% of all lab-confirmed cases'.

However, despite the 'high number' of confirmed total flu cases (99,829), the season was clinically less severe than 2014. The report also noted that emergency department visits were about average and ICU admissions were slightly down, with a similar proportion of A- and B-strain infections.

Will 2016 be a repeat of 2015? Seasonal flu is so unpredictable that even the experts don't know which strains will eventually come to the fore during the winter flu season, which is what makes deciding on the vaccine formulation such a challenge.

Corporate travellers could benefit

The Influenza Specialist Group (ISG), Australia's expert body on influenza, is less than equivocal in its advice to the nation's GPs for the 2016 flu season:

"Surveillance data indicates that, in some influenza seasons, QIV should provide better coverage than TIV against influenza B because the type B lineage(s) that circulate in any given season are not totally predictable. However, the degree to which QIV will translate into additional clinical protection for patients when compared to TIV remains to be demonstrated clinically. TIV vaccine will provide equal protection against the 3 strains common to both TIV and QIV in any particular season and is therefore preferred over delayed or non-vaccination."

ISG Chairman Dr Alan Hampson believes the new four-strain vaccine is certainly worth considering for two groups in particular.

Firstly, there's those who are more susceptible to severe flu infection – young children, the elderly and anyone with an underlying medical conditions. Corporate travellers are more likely to have greater exposure to flu strains that are already circulating, as well as to new strains that could emerge outside Australia. Business people who fly regularly, domestically and internationally, particularly to Asia should consider four strain vaccinations.

"Type B flu virus occasionally predominates in parts of Asia," Dr Hampson said. "If you're travelling and you really want to avoid influenza, the quadrivalent vaccine may make good sense."