By Ho Binh Minh

HANOI, April 6 (Reuters) - Vietnam should accelerate poultry vaccinations and target more ducks in its anti-bird flu campaign, a World Health Organisation official said on Friday.

Hans Troedsson, Representative for the UN agency in Vietnam, said the poultry vaccination campaign helped explain why Vietnam has had no human cases since November 2005.

"It is important that Vietnam needs to step up and further the vaccination," Troedsson told Reuters after a ceremony to mark the World Health Day.

The H5N1 virus has killed 42 people in half of the Southeast Asian country"e;s 64 provinces since the virus re-surfaced in Asia in late 2003. It flared up again among poultry in the south late last year and earlier this year.

Troedsson said the campaign should target ducks.

Waterfowl are a reservoir for the disease and can spread the H5N1 virus in their droppings as they roam through rice fields. Ducks often show no symptoms of sickness, making it harder to contain the virus.

Last week, the virus was confirmed to have killed 65 ducklings in the southern province of Ca Mau, two weeks after Vietnam lifted a ban on hatching waterfowl.

Vietnam plans to use 500 million doses of Chinese and Dutch vaccines this year and next. The Agriculture Ministry said it would vaccinate up to 90 percent of poultry to prevent the return of the virus in winter, when bird flu seems to thrive best.

Experts fear that although H5N1 does not appear to have developed the ability to spread easily from person to person, it could do so and set off a pandemic in which millions could die.

Health Minister Trang Thi Trung Chien said bird flu posed "the highest risk to public health" given its complexity and the risk of turning into a pandemic.

Speaking at the ceremony on Friday, she said Vietnam always considered pandemic prevention its top priority and would work closely with foreign governments and international organisations in sharing information and expertise in the fight.

Bird flu has killed at least 170 people worldwide, most of them in Vietnam and Indonesia, WHO figures show.

On Thursday, Egypt"e;s health ministry said a two-year-old girl tested positive for bird flu, bringing to 33 the number of human cases in the most populous Arab country.

Indonesia has the world"e;s highest toll with 63 deaths, according to the WHO, while Indonesia"e;s health ministry says 72 have died.