Cold-attenuated live influenza vaccines, a risk-benefit assessment

The principle of live attenuated influenza vaccines has been known for many decades. However, the pharmaceutical and clinical development according to current regulations, of modern live influenza vaccines based on cold adapted influenza viruses (CAIV) started only recently and these vaccines will most probably become an alternative within the next couple of years to licensed inactivated influenza vaccines that have been used routinely since the early 1940s. In contrast to contemporary trivalent inactivated influenza vaccines, which are administered intramuscularly, trivalent CAIV-based vaccines will be administered intranasally as a spray. Quality, safety and efficacy aspects related to CAIV vaccines as well as possible risks linked to the widespread use of these vaccines will be discussed in the following overview and compared to established influenza vaccines. Moreover, issues of practicality of CAIV vaccines focusing on the necessity of an annual update of influenza vaccines are addressed.