Merck & Co's cervical cancer vaccine Gardasil has received the safety thumbs-up by a major study published online in the British Medical Journal.

An Australian survey of 380,000 schoolgirls and young women given the vaccine found only 25 suspected hypersensitivity reactions – and subsequent tests suggested only three of the 25 girls were actually hypersensitive.

All the recipients, aged 12 to 26, received Gardasil in April last year as part of a national secondary school immunisation programme. The research team led by Dr Sharon Choo from the Royal Children's Hospital, Melbourne, Australia, identified 25 schoolgirls who might have had hypersensitivity reactions to the vaccine, and gave it to them again.

They monitored the schoolgirls and followed them up by telephone one week after subsequent doses to see if there were any more adverse events. Seventeen of the 18 girls given Gardasil again had no reaction to the new doses. One girl reported limited urticaria (hives) after the vaccine was given, while skin-prick tests conducted on 19 of the girls were negative.

The researchers said the data suggests that true hypersensitivity is rare and reactions such as hives are often one-off events and do not increase the risk of adverse reactions in subsequent vaccinations. The study results will be relief for Merck following persistent safety concerns over a vaccine that is given to healthy children.

At the start of this year, the European Medicines Agency said there had been two sudden and unexpected deaths in young women who had received Gardasil to protect them from cervical cancer. However, the EMEA decided that the benefits of Gardasil outweighed the risks and did not order product information changes.

The authors of the BMJ article say their study should reassure users and healthworkers about the vaccine's safety. However, they note that some components of the vaccine, such as aluminium salts and yeast, had previously been associated with hypersensitivity reactions.

They recommend that girls with suspected hypersensitivity to Gardasil should be evaluated before receiving more doses and also call for more research into why some people show hypersensitivity to the vaccine.