Influenza or ‘the flu’ is a major respiratory pathogen.
The WHO estimates that each year it causes 1 to 4 million cases of severe illness and 250,000 to 500,000 deaths (WHO, 2009). Influenza mortality mainly affects the very young and elderly. It is also a major cause of work absenteeism, leading to an estimated 87 billion USD productivity loss in the US each year alone (CDC Foundation, 2014).
The best way to protect against flu is through vaccination. The WHO estimates that worldwide roughly 4 billion USD is spent per annum on influenza vaccines (WHO, 2010). Vaccination in the case of flu involves a yearly injection of attenuated or dead influenza viruses to induce immunity in the form of the antibodies against the circulating seasonal influenza strains. The induction of antibody-producing cells through vaccination allows the immune system to prepare to defend the body against the influenza virus circulating during the winter months.
However, the current influenza vaccines have serious shortcomings. The current vaccines induce antibodies which target regions of the virus that are highly variable. They therefore have to be (i) administered yearly, (ii) updated every few years, (iii) and typically provide protection to only 50% of the individuals who receive it. Finally, the current vaccines need to be formulated 6 months prior to influenza season and so the strains that are subsequently prevalent in the actual flu season do not always match the strains used in the vaccine, leading to even further reductions in protection (Paules & Subbarao 2017).