Information found by internet search engines is biased against the vaccination of children, according to a survey.

A report published in the Archives of Disease in Childhood journal shows that the top 10 results from popular search site Google all referred to anti-vaccination sites.

Many of them purported to give both sides of the argument, but very few of them did, the BBC reported.

More than 55 per cent of adults with internet access use the web for health information, and some doctors are concerned that official sites run by governments or expert groups have equal status with those set up by people with no medical qualifications.

Researchers from the University of Sydney typed the words 'vaccination' and 'immunisation' into seven search engines, including Google, Yahoo, Lycos and Altavista.

In total, 43 per cent of the links led to anti-vaccination sites, including what the researchers described as "quasi-official" sites with referenced material from medical journals.

Others were personal testimonies, 'back to nature' appeals and sites alleging cover-ups and conspiracies involving doctors, governments and pharmaceutical companies.

Lead researcher Professor Simon Chapman told the BBC: "Many of them referred to the medical literature, but not in a way which was coherent or comprehensive."

He explained that the most disturbing aspect is that a parent going to the web to search out information is going to have a very high probability of arriving at such a site.

"They look authoritative and they have a lot of information, but many of them are really very irresponsible," concluded the professor.