Abstract

Until recently influenza vaccines have always been administered by deep subcutaneous or intramuscular injection. They provoke the appearance of antibodies in the blood against both the haemagglutinins and the neuraminidases of the viruses they contain. On the whole, the protection they afford is related to the titres of these antibodies in the blood. However, the mechanism of immunity against influenza is complex and some workers have suggested that local antibodies in the nose and upper respiratory tract (IgA) are more effective in protection than those circulating in the blood (mostly IgG). These antibodies have been claimed to be more effectively elicited by a vaccine administered as a fine intranasal spray instead of being injected. A nasal spray would avoid the risk of a sore arm.