AstraZeneca's four-strain flu vaccine cleared in US

AstraZeneca's Medimmune division has won approval in the US for FluMist Quadrivalent, the first seasonal influenza vaccine to provide protection against four strains of the virus in a single shot.

There are two types of influenza viruses that cause illness and death in people: influenza A and B.

Each year, manufacturers make seasonal influenza vaccine that includes two strains of influenza A and one of influenza B, as advised by the World Health Organization (WHO) and drug regulatory authorities.

At the moment all other licensed seasonal influenza vaccines currently available in the US are trivalent, containing three strains (two strains of type A influenza (A/H1N1 and A/H3N2) and one B lineage strain).

During a typical influenza season, however, there may be two different influenza B strains circulating, or the B strain selected for inclusion in the trivalent influenza vaccine may not be the influenza B strain that eventually circulates causing illness.

To answer that eventuality FluMist Quadrivalent contains an additional type B lineage strain to help provide broad protection against circulating influenza A and B, said AstraZeneca.

The FDA has approved the new vaccine for use in people aged between two and 49 years. Like the original FluMist vaccine - which achieved sales of $161m in 2011, a 7 per cent decline on 2010 - the new product is administered as a spray into the nose.

"We believe that the inclusion of an additional B strain in an annual influenza vaccine could provide a direct health benefit to individual vaccine recipients in the event that the correct B lineage either is not selected for inclusion in a trivalent vaccine, or if both lineages co-circulate," commented Bahija Jallal, MedImmune's executive vice president of R&D.

Having the extra spread of B strain protection will be of particular benefit in younger age groups, according to the FDA.

"Illness caused by influenza B virus affects children, particularly young and school-aged, more than any other population," said Karen Midthun, director of the FDA's Center for Biologics Evaluation and Research (CBER).

"A vaccine containing the four virus strains most likely to spread and cause illness during the influenza season offers an additional option to aid in influenza prevention efforts," she added.