TORONTO (Canadian Press) -- U.S. scientists are reporting they've made progress in the search for what's called the Holy Grail of influenza research -- a universal flu vaccine.

In a report in the journal Science, they show that a two-step vaccine they developed protected mice, ferrets and monkeys against a broad range of flu viruses.

The first part of the vaccine targets a portion of flu viruses that remains fairly constant even when the rest of the virus changes.

By generating antibodies to that region of the virus, the vaccine was able to protect the animals against viruses from 1934 all the way to 2009, something a regular flu shot could not do.

The senior author, Dr. Gary Nabel, says he thinks of the work as a proof of concept that a universal flu vaccine can be developed.

He says if things continue to go well with the research a trial to see if the model will work in people could be started in about three years.

Copyright The Canadian Press, 2010