Influenza is a common and acute respiratory illness that is estimated to cause 1,400 deaths, 18,000 hospitalisations, and over 300,000 general practice consultations in Australia each season¹.

At 21 November, 2016, there had been a total of 86,240 laboratory confirmed notifications of influenza in Australia⁹. With this high infection rate, the Australian Government Department of Health Australian Technical Advisory Group on Immunisation (ATAGI) strongly recommends an influenza vaccination as the most important measure to prevent influenza and its subsequent complications². Whilst the immunisation schedule for influenza is straightforward with one injection each season (typically at the beginning of autumn³), the strains of circulating influenza, the types of influenza vaccine available, and your individual risk is more complex.

The two subtypes of influenza virus (influenza A and influenza B) account for most influenza diseases amongst humans. Though the subtypes do not change from A and B, the strain (or lineage) of the disease varies from year to year. It is for this reason that annual vaccination is recommended due to the changing predominant strains that are circulating. The composition of the vaccine is determined each year by the Australian Influenza Vaccine Committee based on information and recommendations from the World Health Organization⁵ and is tailored to best protect against the predominant strains circulating at the time.

Historically, there have been three strains of influenza immunity within the Australian vaccine; two influenza A strains and one influenza B strain. Vaccinations prior to 2014 provided immunity against three strains from the A and B subtypes and is called a trivalent vaccine. However, in 2015 a four strain (quadrivalent) vaccine became registered for use in Australia which included immunity against an additional influenza B strain⁴. This additional vaccine was developed to provide broader protection against circulating flu viruses. The effectiveness of the influenza vaccine depends on the age and the immunocompetence of the recipient and the degree of similarity between the virus strains in the vaccine and those circulating in the community⁷. The two influenza B virus strains available in the quadrivalent vaccine are of different lineages, thus the trivalent vaccine will only protect for three out of four circulating virus strains while the quadrivalent will protect against all four. The quadrivalent vaccine increases human immunity against influenza and with recent research indicating substantial differences between influenza A and influenza B (the B strain in the trivalent vaccine being a mismatch 25% of the time⁶), the quadrivalent vaccine is now recommended by the ATAGI in preference over the trivalent. The 2015 influenza season saw both influenza A and B subtypes circulating. The proportion of all circulating influenza viruses attributable to the influenza B lineage that is not included in the TIV varies. This has ranged from 0% (in 2000 and 2001) to 32% in 2008⁸. These statistics reinforce the recommendation for the quadrivalent vaccine against possible contraction of influenza.

The importance of the quadrivalent vaccine comes after the 2015 season saw a late recommendation from the World Health Organisation to include influenza B in the vaccine. The subsequent 2015 flu epidemic resulted with over 12,000 influenza cases up to August with influenza B being the dominant influenza type nationally⁷.

Sonic HealthPlus offers a national flu immunisation program available within our clinics and on-site at your workplace. With clear evidence suggesting the quadrivalent vaccine offers better protection against circulating strains, our 2017 flu program will consist only of the quadrivalent vaccine. This approach ensures we can assist your workforce by providing active immunisation against the strains of circulating influenza.