With the ability to cause an epidemic or even a pandemic, the recent Australian flu virus or H3N2v currently has the World Health Organisation (WHO), National Health Service (NHS) and Public Health England (PHE) taking serious precautions as the number of incidences has over doubled from last year’s figures. Many variants of Influenza A (such as H3N2v) exist and are categorised by the antigenic properties of the virus surface glycoproteins; Hemagglutinin (HA) consisting of 18 subtypes (H1-H18) and Neuraminidase (NA) containing only 11 subtypes (N1-N11). Like with many other infections the majority occur in the elderly (≥80 years), children (5-9 years) and people suffering from long term illnesses such as diabetes.
H3N2 is a non-human influenza that has developed in pigs and birds and is likely to have a variety of reservoirs in other animals as well. Living in a non-human host allows the virus to develop and mutate (antigenic drift) undetected and therefore consequently gaining the ability to infect humans. For example, swine influenza has similar sialic acid (acidic sugar) types as human and avian influenza, creating the possibility of pigs becoming infected by both types of influenza. This can cause re-assortment of gene-segments and produce a link between avian influenza and human influenza. This is due to the ability of sialic acid found in pigs binding with human and avian influenza strains. H3N2 first originated from Hong Kong, causing a category 2 pandemic in 1968-1969. Interestingly, the variant of H3N2, H3N2v developed through antigenic drift and proves difficult to protect against.
Transmission of H3N2v is difficult to prevent due to avian migration, allowing an unrestricted spread of the virus. The transmission of the virus is global and seasonal, causing various vaccines to be developed seasonally as a reaction to new viral developments. Since H3N2v can asymptomatically infect birds and pigs, it provides an ideal host environment for viral mutation and variation to develop, potentially re-infecting humans as a new strain. This makes vaccine development difficult.
Since the first case of H3N2v in 2011, vaccine development never hit its stride and struggled in effectiveness against H3N2v. The development process for the vaccine has been slow and variants for the virus have already infected people, rendering the current vaccine in progress useless or lowering the percentage of effectiveness against the newer strain. Over time more variants of viruses will begin to appear, in which case the vaccine effective for the original virus would no longer protect against the new variant. This ongoing development and variations amongst viruses is what makes them so effective at spreading throughout the population.