FACTBOX-Making a flu vaccine can take months

April 26 (Reuters) - The U.N. World Health Organization and U.S. Centers 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 (SASY.PA), Australia's CSL Ltd (CSL.AX), GlaxoSmithKline Plc (GSK.L), Novartis AG (NOVN.VX), Baxter (BAX.N) and nasal spray maker MedImmune, acquired by AstraZeneca Plc (AZN.L).

* Experts agree the current process for making vaccines is clumsy and outdated, but new and more efficient technologies are still a few years away.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