SCENARIOS-Children go to front of flu vaccine line

By Maggie Fox, Health and Science Editor

WASHINGTON, July 10 (Reuters) - The World Health Organization plans to release guidance next week on the need for a vaccine against the new H1N1 swine flu virus.

Companies are already working to make one.

Few experts doubt there will be an H1N1 vaccination campaign but questions remain about how much companies should be prepared to make, whether to try to stretch the supply using ingredients called adjuvants and who should get the vaccine.

Here are some potential scenarios:

FULL SPEED AHEAD

WHO could advise companies to switch to full-speed production of an H1N1 swine flu vaccine for the northern hemisphere's autumn, with the goal of getting a maximum 4.9 billion doses ready. More doses would be needed if clinical trials show that people will need two shots a few weeks apart to get the best protection.

Even more doses would be needed if children aged 2 to 9 turn out to need three doses. Currently, unvaccinated children under 9 need two influenza vaccinations the first year to get full protection from seasonal flu.

It is possible WHO will recommend that all age groups be immunized against the new H1N1 virus. Usually, countries issue guidelines for specific age groups, depending on who is worst hit and balanced against vaccine availability.