Now, a nasal spray which could spell the end of the flu jab

The spray works by building up resistance to disease in the nasal passages and stopping the infection taking hold in the body, according to the scientists from Albany Medical College in New York.

Until now nasal vaccines have not offered enough protection to be effective and jabs have remained the most common form of building up immunity. But the new study shows how including a natural immune chemical with standard vaccines can boost their protective effect when delivered via the nose.

Combining standard vaccines for respiratory pathogens with the immune chemical, interleukin-12 (IL-12) and delivering them intra-nasally to mice has been shown to induce high levels of protection, `The Daily Telegraph` reported.

Vaccines against various respiratory pathogens were tested, including influenza virus, pneumococcal bacteria and Yersinia pestis, bacteria used in bio-weapons. IL-12 is a natural immune chemical, known as a cytokine.

It is a powerful stimulator of the immune response through its interactions with other immune chemicals and the white blood cells that produce them, say the scientists.

Prof Dennis Metzger, who led the study, said "Infectious agents still account for around 25 per cent of deaths worldwide and the major killers are acute respiratory infections.

"However, it is difficult to induce immunity at the site of entry and so standard vaccines are only partially protective. Intranasal vaccination gets around this problem by inducing immunity in the pulmonary passage. This prevents initial infection as well as systemic complications."

He added: "Vaccination via a nasal spray is a non-invasive procedure that is easier than administering vaccines by injection.