Nasal vaccine works against Sars

The scientists have three approaches to beating the virus

US scientists have successfully developed a nasal spray version of Sars vaccine that works in monkeys.

This is the third Sars vaccine made by the National Institute of Allergy and Infectious Diseases.

The previous two required two doses to work, had to be injected under the skin and had only been tested in rats.

The new nasal vaccine needs only one dose and is delivered directly into the respiratory tract where Sars attacks, they say in the Lancet.

The NIAID researchers are hopeful that a similar nasal vaccine against Sars could be developed for humans.

With more research, we hope to develop a vaccine based on this approach that could be used to rapidly immunise first responders and other medical personnel Dr Brian Murphy, lead researcher at the NIAID

Like the previous two, the newest vaccine uses a small piece of the virus's DNA to stimulate the body's immune system to mount a protective response.

They took a small piece of DNA from the Sars virus that codes for a protein normally found on its outer surface.

They then put the piece of Sars DNA into a weakened version of a virus that causes respiratory diseases like pneumonia in humans.

Direct delivery

This virus carried the Sars DNA directly into the respiratory tract.

Tests in monkeys showed the vaccine provided protection against Sars without causing infection itself.

Lead researcher Dr Brian Murphy said: "This study shows that delivering the vaccine directly to the respiratory tract can effectively protect primates from Sars.

"With more research, we hope to develop a vaccine based on this approach that could be used to rapidly immunise first responders and other medical personnel, helping them control a potential outbreak," he said.

Dr Murphy says the vaccine in its current form would be most effective in young children. This is because most adults already have some immunity against the common viruses that cause pneumonia.

"In the long run, we want to establish a weakened respiratory virus vector that all people are susceptible to," he said.

Professor Maria Zambon of the Health Protection Agency said: "This represents a significant advance in the fight against Sars, but it's overall importance will be judged against time, when further human trials have taken place.

"The development of new vaccines against any infectious disease usually involves a variety of approaches and methods of delivery."