The US company, acquired by the UK's AstraZeneca in April 2007, is preparing to manufacture some 12 million doses of FluMist - a record for MedImmune - for the 2008-2009 season and intends to continue ramping up production "substantially" in subsequent seasons.

The planned hike in production comes on the back of a recommendation by the Advisory Committee on Immunization Practices (ACIP), which advises the US Centers for Disease Control and Prevention (CDC) on vaccine issues, to widen the scope of the annual influenza vaccination programme to all children aged six months to 18 years. The previous ACIP recommendation was for vaccination of all children between the ages of six and 59 months.

The revised recommendation, which the ACIP wants to take effect as soon as possible, and no later than the 2009-2010 'flu season, expands the number of children eligible for 'flu vaccination in the US by around 30 million.

Immunisation providers should start working towards offering vaccination for all children aged six months to 18 years for the 2008-2009 season if this is feasible, "consistent with the current recommendation that all persons who want to reduce the risk of becoming ill with influenza or transmitting influenza to others should be vaccinated", the Committee said.

Studies have shown that healthy children are significantly burdened by influenza and are at increased risk of needing 'flu-related medical care, the ACIP pointed out. Moreover, there is evidence that reducing influenza transmission among children can also limit the spread of 'flu among their household contacts and the community.

Results from a vaccine efficacy study among children aged six to 23 months were presented at the ACIP's recent meeting in Atlanta. The findings indicated vaccine efficacy of about 75 per cent in preventing hospitalisation due to influenza among fully vaccinated children in this age group during the 2005-06 and 2006-07 seasons.

MedImmune said it "strongly supports the CDC's efforts to encourage vaccination against influenza throughout the season, even if there is evidence that some circulating strains are not well matched to the vaccine". Mismatched strains have limited the effectiveness of the 2007-08 vaccine, warding off influenza in only around 40 per cent of cases.

For the 2008-09 season, the US influenza vaccine will include three new strains: an A/Brisbane/10/2007 (H3N2)-like virus, a B/Florida/4/2006-like virus and the A/Brisbane/59/2007 (H1N1)-like virus strain. The H3N2 and B virus vaccine components in the US vaccine are already included in this year's vaccine for the Southern Hemisphere.

The new strains are likely to present some manufacturing challenges to vaccine producers as they gear up for the 2009-09 season. And while FluMist is the only influenza vaccine available in the US as a nasal spray, MedImmune will be facing competition from manufacturers of more traditional (and less expensive) flu vaccines, such as GlaxoSmithKline, Sanofi-Aventis and Novartis, all of which are boosting production for next year's season.

According to the CDC, 'flu vaccine manufacturers in the US produced as many as 130 million doses of vaccine for the 2007-08 season and "have discussed expanding production in the coming years".

What MedImmune does have is the psychological advantage of needle-free injection, an important consideration in vaccinating school-age children. "Our experience has been that children are generally quite accepting of a vaccine that does not involve a needle," commented Dr Frank Malinoski, the company's senior vice-president of medical and scientific affairs.

Since the US launch of FluMist in 2003, MedImmune has been working to establish vaccination programmes for FluMist in schools and other non-traditional venues for immunisation.

FluMist is administered as a fine mist through the nose. A weakened or attenuated form of the live influenza virus, the vaccine acts in the nasal passages to stimulate an immune response closely resembling the body's natural reaction to 'flu infection.

The use of live vaccine viruses may explain why some protection against mismatched 'flu strains has been observed with FluMist in past seasons, MedImmune said.

For example, in a head-to-head clinical trial conducted during the 2004-05 influenza season with more than 4,000 children aged two to five years, and looking specifically at mismatched virus strains, there were 52.4 per cent fewer cases of 'flu in children given FluMist than those receiving a conventional 'flu shot, the company noted.

MedImmune can also capitalise on the expanded age indication approved for FluMist by the US Food and Drug Administration (FDA) last September. The FDA cleared the vaccine for active immunisation to prevent disease caused by influenza A and B viruses in children and adults aged two to 49 years.

Previously, concerns about wheezing problems in some children under five had limited FluMist to an age range of five to 49 years. On top of that, a final FDA decision on MedImmune's supplemental biologics licence application to widen the target population for FluMist was delayed last year by good manufacturing practice violations at the company's facility in Speke, UK.

With these problems now resolved, MedImmune should now be in a position to make the most of an expanding US market for FluMist in children and adolescents. Another fillip to the company's 'flu vaccine business was FDA approval in January 2007 for a new formulation of FluMist that can be refrigerated rather than frozen.

The previous frozen version had limited usage of FluMist by creating storage difficulties for vaccine providers.