The annual production cycle for influenza vaccine.

Influenza disease impacts every year up to 10% of the world's population, i.e. up to 500 millions of people. The international surveillance network organised by WHO allows the detection of important antigenic variation of the virus in humans but also animals (especially birds and pigs). Epidemiological data are summarised twice a year in two meetings (one in February, the other in September) allowing WHO to propose new recommendations for vaccines formulations for each northern and southern hemisphere influenza season annual vaccination. According to such recommendation, vaccine manufacturers proceed each year with two different vaccine production campaigns in order to match the vaccine composition with global epidemiological surveillance data and so, develop each time an updated vaccine formulation. To date within 6 months production periods, almost 250 million of doses are brought annually on market in more than 100 countries. In such a tight schedule, the annual production requires careful coordination of a highly complex process involving both public health laboratories and vaccine companies, in order to provide on time safe and effective vaccines. Major steps of this vaccine production process including the milestones and the bottlenecks need to be detailed in order to well understand difficulties and hurdles towards increase of global capacity and introduction of new vaccines.