Dutch scientists say that vaccinating chickens against avian flu can prevent a major outbreak of the disease by stopping birds from passing on the virus.

Although vaccination is recognised as one of the main weapons in the fight against bird flu, scientists did not know if vaccination protected only treated birds or had wider benefits.

Scientist Jeanet Van der Goot believes that vaccination of poultry can prevent a major outbreak of highly pathogenic avian flu viruses.

Van der Goot and fellow researchers say that vaccination reduces the infectiousness of chickens with avian flu and also the susceptibility of healthy chickens to the virus, but it might take two weeks after vaccination before transmission to other birds was completely blocked.

The study comes as governments around the world are trying to contain Asia’s deadly H5N1 strain of bird flu.

The H5N1 strain is endemic in poultry in parts of Asia and has killed more than 60 people.

Experts fear the virus could mutate into a form passed easily from person to person, sparking a pandemic in which millions could die.

China has announced plans to vaccinate billions of birds to halt the spread of H5N1, while the World Organisation for Animal Health has urged Indonesia and Vietnam to step up vaccination.

Researchers at the Dutch Central Institute for Animal Disease Control have conducted experiments since 2003 with two vaccines against H7N1 and H7N7 avian flu strains, proving their effectiveness in blocking the spread of the viruses.

Van der Goot and colleagues are currently experimenting with vaccines against H5 avian flu, and expect results some time next year.

They say their results are very good and important news for the world because previously nobody really knew whether chicken vaccines could stop the spread of bird flu.

In one experiment, the Dutch scientists housed infected and healthy chickens together to track the transmission of the virus; all birds were vaccinated in advance.

In results two weeks after vaccination, it was seen that both of the tested vaccines were able to completely block the spread of the disease.

In a second set of experiments, researchers paired a vaccinated and infected chicken with a non-vaccinated, healthy chicken and the virus did not transmit again.

Van der Goot says that the results showed that the two vaccines worked only after two weeks, and that in any period shorter than two weeks, the viruses still spread.

Van der Goot said the H7N1 vaccine used in the study was based on a strain found in Italy and the H7N7 one was based on a strain found in Pakistan.

The Netherlands was hit by a H7N7 outbreak in 2003, which led to one human death and wiped a third of the flock in one of the world’s leading poultry exporting countries.

The study is published in the Proceedings of the National Academy of Sciences.