FACTBOX-Making a flu vaccine can take months

(Reuters) - The U.N. World Health Organisation and U.S. Centres for Disease Control and Prevention have been collecting samples of the new H1N1 swine flu virus to make a new vaccine in case it is needed.

Following are some facts about influenza vaccines.

* The WHO and CDC prepare samples of virus to give to industrial makers.

* These samples must be grown in specially produced chicken eggs. The virus is then purified and made into vaccines, a process that takes months.

* At least 20 companies make flu vaccines including Sanofi Pasteur, Australia's CSL Ltd, GlaxoSmithKline Plc, Novartis AG, Baxter and nasal spray maker MedImmune, acquired by AstraZeneca Plc.

* Experts agree the current process for making vaccines is clumsy and outdated, but new and more efficient technologies are still a few years away.

* WHO and CDC experts are trying to decide if a new vaccine for the H1N1 swine flu strain is needed, or perhaps if a fourth element could be added to the seasonal flu vaccine mix for next September.

* The health agencies also had been considering adding some vaccines against H5N1 avian influenza, which occasionally infects people and is also considered a major pandemic threat.

* Tests show the H1N1 component of the current seasonal flu vaccine does not protect against the new strain.