Double doses of vaccine may be needed if humans are hit by a bird flu epidemic, British researchers have warned.
A study in Leicester, UK, has found that a second dose of vaccine has a dramatic impact on immunity and protection against flu.
The study involved volunteers who received their first shot of a new H5 vaccine seven years ago. Bird flu, or H5N1, is a strain of H5 flu.
The study found that a booster shot of the vaccine gave 80 per cent of volunteers protection against all strains of H5 vaccine.
But a single shot given to new volunteers was ineffective – until they were given a second vaccination. The vaccine took effect after six weeks.
The findings were reported last night in the New England Journal of Medicine.
The finding suggests that a flu epidemic could be prevented – but would place pressure on world health resources as big stockpiles of vaccine would be needed.
Researcher Dr Iain Stephenson, of Leicester University, said: "In the event of the next influenza pandemic, vaccination will be the best way to protect people. Because of manufacturing capacity constraints, vaccines ideally need to be as a low dose as possible so that limited antigen material can be optimally used.
"In addition, it generally takes two doses of vaccine to give a good response, so if a pandemic occurred it would take some time to produce vaccine and then administer two doses to protect people.
"Therefore stockpiling of vaccines has been suggested to overcome some of these difficulties. However, subjects will still require two doses to generate protection and if the pandemic spreads rapidly this could be challenging to deliver."
New England Journal of Medicine (October 9 2008)
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