A DNA-based vaccine against avian influenza can safely stimulate the immune system to levels expected to protect against flu, San Diego-based Vical Inc reported yesterday.

It said tests on 100 volunteers showed 67 had immune responses that could protect against infection with the H5N1 avian flu virus, with no serious adverse reactions after two injections.

The Phase I clinical trial, meant to demonstrate the vaccine is safe, was continuing, Vical said in a statement.