FACTBOX: Making a flu vaccine can take months

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* Experts agree the current process for making vaccines is clumsy and outdated, but new and more efficient technologies are still a few years away.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

* Consulting firm Oliver Wyman found that drug companies would need four years to meet global demand for vaccines if a pandemic broke out today, but new technology could significantly boost production by 2014.

* Currently, drug makers could make up to 2.5 billion doses of pandemic vaccines in one year, meaning it would take four years to meet global demand, Oliver Wyman found. In a best-case scenario, they could make 7.7 billion doses in 1.5 years.

* Compounds called adjuvants can be used to boost a vaccine's effectiveness, so it could be diluted and used in more people.

* Current global demand for seasonal influenza vaccine is about 500 million doses a year.

* The CDC recommends that 261 million Americans -- 85 percent of the population -- should be vaccinated against flu. A RAND Corp. study in December showed that only about a third of those who should have did get the vaccine.

(Reporting by Maggie Fox; Editing by Will Dunham)