HONG KONG, Sept 25 (Reuters) - Delivering flu vaccines straight into the lungs instead of through routine injections could trigger a far stronger immune response, a study has found.

The world is expected to be extremely short of vaccines in the event of a flu pandemic, so the search for the best way to deliver vaccines is important because it would economise on the quantity of each dose.

The Australian study, published in Mucosal Immunology, showed that lower doses of a seasonal flu vaccine delivered into the lungs of sheep gave better protection against flu than a higher standard dose that was injected into another group of sheep.

"Our results suggest that delivery by the lung may allow a much lower ... dose to be used in the influenza vaccine, while inducing equivalent or perhaps even improved protection. This would mean more people would quickly be able to receive the vaccine," associate professor Philip Sutton of the Centre for Animal Biotechnology at the University of Melbourne wrote in an email to Reuters.

The scientists delivered three different doses of flu vaccines (15, 5 and 1 micrograms) into the lungs of three groups of sheep using a bronchoscope, or tube. A fourth group of sheep was injected with standard 15-microgram flu vaccines.

"Lung delivery produced superior levels of antibodies in the lung (approximately 1,000 times more), where the influenza virus infects, than the injected vaccine. The antibodies produced in the blood and lung were able to block the ability of the virus to stick to the receptor it uses to infect cells, demonstrating they would be effective against infection," Sutton said.

The generation of such huge amounts of antibodies in the lungs was especially important in the case of influenza, because flu is spread from person to person mainly through sneezing and coughing.

"The generation of functional antibodies in the lung could potentially help reduce the spread of the infection by neutralising the virus before it can be breathed out by an infected person," Sutton said.

He noted, however, that they would need to find better ways to deliver vaccine directly into the lungs. (Reporting by Tan Ee Lyn; Editing by David Fogarty)

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