* Genetic code of virus available, virus samples awaited
* Production process will take months
* Focus on adjuvants to make sufficient quantities
By Ben Hirschler
LONDON, April 28 (Reuters) - Manufacturers have taken the first preparatory steps in developing a vaccine against a new strain of flu that has killed up to 149 people in Mexico and threatens to become a pandemic.
Switzerland's Novartis AG said on Tuesday it had received the genetic code of the new virus strain, enabling it to start work on evaluating production, and it hoped to receive the actual virus in its laboratories "in the near future".
Still, it is likely to take between five and six months before a vaccine is commercially available, according to the World Health Organisation.
The delay is not for want of trying.
The U.S. Centers for Disease Control and Prevention has already taken a sample of the H1N1 virus causing the disease, produced a vaccine virus strain and is growing it up, marking the first stage of the production process.
These samples, which can then be distributed to companies, must be grown in specially produced chicken eggs in a cumbersome system that experts agree is outdated. New and more efficient technologies based on cell cultures are, however, still a few years away.
At least 20 companies, in addition to Novartis, make flu vaccines, including Sanofi-Aventis, GlaxoSmithKline, Baxter International, Australia's CSL and nasal spray maker MedImmune, now part of AstraZeneca.
They are currently geared to producing season flu shots, which vaccine specialists say will not stop the new form of swine flu spreading around the world, although people who have been immunised may end up with milder symptoms.
So-called swine flu is a variant of the H1N1 form of the human influenza virus, but tests show the H1N1 component of the current seasonal flu vaccine does not protect against the new strain.
A big challenge facing manufacturers will be making sufficient quantities of vaccine from a limited supply of active ingredient, or antigen.
Companies and health authorities will also have to decide how far to switch capacity from producing seasonal vaccines to making the new vaccine -- a tricky process of balancing risks.
One option to extend supply is to use an additive, known as an adjuvant, to increase the body's immune response and reduce the amount of antigen needed in each shot.
Several companies are working on this approach. Glaxo, in particular, said it believed its novel adjuvant technology could make a significant contribution to antigen sparing.
The British company previously developed a vaccine against the H5N1 strain of bird flu -- originally thought to pose the biggest pandemic threat -- using a special adjuvant that allowed an extremely low dose of active ingredient to be used. (Editing by Will Waterman)