NEW YORK (Reuters Health) - An experimental flu vaccine made in insect cells -- not eggs, where flu vaccines currently available in the US are grown -- has proven to be safe and as effective as conventional vaccines in protecting people against the flu, researchers reported Tuesday.

There are a number of drawbacks to producing vaccine in eggs. Using eggs to grow vaccine is time-consuming; a vaccine made from insect cells could be produced in large quantities much more quickly, a key advantage if bird flu pandemic were to strike.

"Eggs can be very cumbersome to work with," Dr. John J. Treanor, from the University of Rochester in New York, added in a statement.

"When you need hundreds of millions of fertilized eggs, you're dealing with a whole host of agricultural issues, as well as scientific concerns regarding the flu virus itself. Flu viruses can be temperamental, and it's not always an easy matter to get the virus to grow as you want in eggs," he added.

The ability to generate vaccine without using eggs is important, given the growing threat of pandemic bird flu.

Treanor's team assessed the safety and effectiveness of an influenza vaccine called FluBlOk from Meriden, Connecticut-based Protein Sciences Corp, which was created through a production method not requiring eggs. The method relies on a virus known as baculovirus, which normally infects insects, to churn out the key components of the flu virus in cells taken from catepillars.

In the study funded by the company, 460 healthy adults were randomly assigned to receive the experimental vaccine at one of two dosages (75 micrograms or 135 micrograms) or placebo during the 2004-2005 flu season.

The investigators report that the vaccine was well tolerated and the side effects were similar to those usually reported from a typical flu shot -- mainly mild arm pain.

Moreover, in the months that followed, seven people in the placebo group came down with the flu, compared with just two people who got the smaller dose of the vaccine. No one who got the higher dose of the flu vaccine developed the flu.

Together, the two vaccines reduced the flu infection rate by 86 percent, according to a report in the Journal of the American Medical Association.

"The preliminary demonstration of protective efficacy in adults provides further support for the development of this promising approach for prevention of seasonal and pandemic influenza," the researchers state.