Two vaccines tested by a Dutch veterinary research center have proved effective against highly infectious bird flu in a first experiment conducted under a controlled environment, the Dutch government said on Friday.

"Not only did the vaccines give poultry used in the lab protection against disease symptoms but they also countered the spreading of the bird flu," the government said in a statement.

One vaccine was produced by France's Ceva Animal Health and the other by Germany's Boehringer Ingelheim, an official document on the Dutch government website showed.

Avian influenza, commonly called bird flu, has been spreading around the world in the past year, killing more than 200 million birds - and six million in the Netherlands alone - sending egg prices rocketing and raising concern among governments about human transmission.

Some countries including China already vaccinate against bird flu and as the virus seems to have become endemic some other governments around the world that have opposed vaccines are reconsidering. Their opposition centered on fears a vaccine could mask the spread of bird flu but tests indicate it would not be the case with the two vaccines tested in the Netherlands.

As part of a European program, the Netherlands has been testing bird flu vaccines for egg-laying hens while France is carrying out tests on ducks, Italy on turkeys and Hungary on Pekin ducks.

Most of these tests are based on existing vaccines and adapted to the particular H5N1 strain that has been spreading in Europe.

The Wageningen Bioveterinary Research, located northeast of Amsterdam, had carried out tests on four chicken vaccines before selecting those of Ceva Animal Health and Boehringer Ingelheim. The other two vaccines that were tested were produced by Bulgaria's Huvepharma and Merck Sharp & Dohme (MSD) respectively, the official document showed.

"I'm happy that we have two vaccines with which we can take the vaccination process against bird flu forward. I'm putting in the next steps as quickly as possible but in a responsible way (...)," Dutch Minister of Agriculture Piet Adema said in the statement.

A field trial will be launched to see whether the vaccines that work in a laboratory setting are also effective if applied in wider conditions.

The trial should take more than a year to give an idea of how long chickens are still immune after vaccination, Adema said in a letter to the President of the House of Representatives dated Friday, also available on the government website.