For years, flu vaccines were designed to protect against three different flu viruses (trivalent). This included two influenza A viruses and one B virus. Experts had to choose one B virus, even though there are two very different lineages of B viruses that both circulate during most seasons. This meant the vaccine did not protect against the group of B viruses not included in the vaccine. Adding another B virus to the vaccine aims to give broader protection against circulating flu viruses.
Influenza is a highly infectious acute viral illness. In healthy individuals influenza is generally self-limiting, but complications such as pneumonia may cause serious illness.
Influenza vaccination can protect against infection. When the flu immunisation programme was initiated the influenza vaccine recommended in elderly people and clinical risk groups in the UK was inactivated trivalent, i.e. containing two influenza A strains and one influenza B lineage, decided each year according to recommendations from the World Health Organization (WHO) . There is limited cross-protection between the two influenza B lineages, so the effectiveness of each season’s vaccine against influenza B depends on correct prediction of the circulating B lineage. Both influenza B lineages have circulated concurrently in recent years, which can limit the effectiveness of the trivalent vaccine against influenza B. In the UK, the vaccine influenza B lineage and the circulating influenza B lineage were at least partially mis-matched in six of the ten influenza seasons from 2000/2001 to 2009/2010.
A quadrivalent influenza vaccine including both influenza B lineages could potentially improve protection against influenza B infection and reduce morbidity and mortality due to influenza B disease. This quadrivalent vaccine (licensed for all individuals 3 years and older) was introduced in the UK in the autumn of 2013.
In a study done by GlaxosmithKline (GSK) over a ten year period between 2000/01 and 2010/11 the use of a quadrivalent flu vaccine rather than a trivalent vaccine could have resulted in an estimated 17,088 fewer cases of influenza each year.
When booking your flu vaccine this year ask your provider exactly what you are getting!