Kirsty Armstrong SRN FPcert BSc(Hons) NPDip PGCert Ed PGDip Senior Lecturer/Practitioner in Primary Care St George’s Hospital London
Influenza is an acute infection caused by a virus. Three category strains – A, B and C – are used in the formulation of the vaccine each year. These strains are those most prevalent in the worldwide spread of influenza. The virus does exhibit antigenic drift most seasons and antigenic shift periodically.1 This means a new formulation of the vaccine is needed every year.