Promises and challenges of live-attenuated intranasal influenza vaccines across the age spectrum: a review.

Despite the availability of inactivated influenza vaccines, influenza continues to cause considerable mortality in the elderly, and morbidity in all age groups. Cold-adapted, live-attenuated, intranasally administered influenza vaccines, first developed in the 1960s, have been tested in more than 10,000 volunteers and have been shown to be safe, well-tolerated, and immunogenic. Recent trials suggest that efficacy in children may be superior to that of inactivated vaccines, and efficacy in healthy adults may be similar to that of inactivated vaccines, although there are limited data comparing the two vaccines directly. Advantages of the live-attenuated vaccines include acceptability, ease of administration, and the potential for mass immunization. The possibility of substantially higher vaccination rates across all age groups brings promise for the development of herd immunity and greatly improved control of influenza in the future.