The World Health Organization says poor countries will find it difficult to get vaccines for the A/H1N1 flu as the world's manufacturing capacity is limited.

WHO chief Margaret Chan made the remarks in Geneva on Tuesday. Meanwhile, the WHO says countries around the world may need to adjust their vaccination plans as production and trials could take longer than expected.

WHO director-general Margaret Chan says the shortfall in worldwide vaccine supplies is due to limited global manufacturing capacity, rather than issues of intellectual property.

"The shortfall in vaccine supplies, in the face of universal need, is the result of limited global manufacturing capacity rather than intellectual property issues."

However, she says ability to pay, whether at the individual or the national level, remains a distinct advantage.

"In the field of health, public policy will remain imperfect as long as access to life-saving interventions is biased in favor of affluence."